Glosario

Glossary
1X
First phase of third-generation (3G) mobile wireless technology for CDMA2000 networks.
1XEV
Evolutionary phase for 3G for CDMA2000 networks, divided into two phases: 1XEV-DO
(data only) and 1XEV-DV (data and voice).
2-Way
Adjacency state for OSPF that shows bidirectional communication between two neighbors
has been established.
3GPP
Third-generation Partnership Project. Created to expedite the development of open,
globally accepted technical specifications for the Universal Mobile Telecommunications
System (UMTS).
A
accept
JUNOS software syntax command used in a routing policy or a firewall filter. It halts
the logical processing of the policy or filter when a set of match conditions is met. The specific
route is placed into the routing table or announced to a neighbor. An IP packet is forwarded to
the next hop along the network path.
action
Within a routing policy or firewall filter, an action denotes a specific function to perform
on a route or IP packet.
active route
Route chosen by a router from all routes in the routing table to reach a specific
destination. Active routes are installed into the forwarding table.
add/drop multiplexer (ADM)
SONET functionality that allows lower-level signals to be
dropped from a high-speed optical connection.
address match conditions
The use of an IP address as a match criterion in a routing policy
or a firewall filter.
Address Resolution Protocol (ARP)
Protocol for mapping IP addresses to MAC addresses.
adjacency
Link-state network neighbor status that represents two neighbors who have
exchanged their link-state database information with each other.
Adjacency-RIB-In
Logical software table that contains BGP routes received from a specific
neighbor.
Adjacency-RIB-Out
Logical software table that contains BGP routes to be sent to a specific
neighbor.
aggregation
Combination of groups of routes that share the same most significant bits into
a single entry in the routing table.
Glossary
535
Alternate Priority Queuing (APQ)
Dequeuing method that has a special queue, similar to SPQ,
which is visited each time the scheduler moves from one low priority queue to another low priority
queue. The packets in the special queue still have a predictable latency, although the upper limit
of the delay is higher than that with SPQ. Since the other configured queues share the remaining
service time, queue starvation is usually avoided. See also
Strict Priority Queuing (SPQ)
.
American National Standards Institute (ANSI)
The United States’ representative to the ISO.
See also
International Organization for Standardization (ISO)
.
application-specific integrated circuit (ASIC)
Specialized processors that perform specific
functions on the router.
area
Routing subdomain that maintains detailed routing information about its own internal
composition and that maintains routing information that allows it to reach other routing subdomains.
In IS-IS, an area corresponds to a Level 1 subdomain. In IS-IS and OSPF, an area is a
set of contiguous networks and hosts within an Autonomous System that have been administratively
grouped together.
area border router
Router that belongs to more than one area. Used in OSPF. See also
Open
Shortest Path First (OSPF)
.
ASBR Summary LSA
OSPF link-state advertisement sent by an ABR to advertise the router
ID of an ASBR across an area boundary. See also
Autonomous System boundary router
.
AS external-link advertisements
OSPF link-state advertisement sent by AS boundary
routers to describe external routes that they know. These link-state advertisements are
flooded throughout the AS (except for stub areas).
AS path
In BGP, the path to a destination. The path consists of the AS numbers of all domains
a packet must go through to reach a destination.
Asynchronous Transfer Mode (ATM)
A high-speed multiplexing and switching method utilizing
fixed-length cells of 53 octets to support multiple types of traffic.
ATM adaptation layer (AAL)
A series of protocols enabling various types of traffic, including
voice, data, image, and video, to run over an ATM network.
ATM Line Interface (ALI)
Interface between ATM and 3G systems. See also
Asynchronous
Transfer Mode (ATM)
.
atomic
Smallest possible operation. An atomic operation is performed either entirely or not
at all. For example, if machine failure prevents a transaction from completing, the system is
rolled back to the start of the transaction, with no changes taking place.
attempt
OSPF adjacency state seen in a Non-Broadcast Multi-Access (NBMA) network that
means the local router is to send a unicast hello packet to a neighbor for which it has not yet
received any protocol packets.
536
Glossary
authentication center (AUC)
Part of the Home Location Register (HLR) in 3G systems, the
AUC performs computations to verify and authenticate the user of mobile phones.
Authentication Header (AH)
A component of the IPSec protocol used to verify that the contents
of a packet have not been changed, and to validate the identity of the sender. The actual
packet data is not protected. See also
encapsulating security payload (ESP)
.
Automatic Protection Switching (APS)
Technology used by SONET ADMs to protect
against circuit faults between the ADM and a router and to protect against failing routers.
See also
add/drop multiplexer (ADM)
.
Autonomous System (AS)
A set of routers under a single technical administration. Each AS
normally uses a single Interior Gateway Protocol (IGP) and metrics to propagate routing information
within the set of routers. Also called
routing domain
.
Autonomous System boundary router
In OSPF, routers that import routing information
external to the protocol into the link-state database.
Autonomous System external-link advertisements
OSPF link-state advertisement sent by
Autonomous System boundary routers to describe external routes that they know. These linkstate
advertisements are flooded throughout the Autonomous System (except for stub areas).
Autonomous System path
In BGP, the path to a destination. The path consists of the Autonomous
System numbers of all the domains a packet must pass through to reach a destination.
auto-RP
One of three methods of electing and announcing the rendezvous point to group
address mapping in a multicast network. A vendor-proprietary specification supported by the
JUNOS software.
B
backbone area
In OSPF, an area that consists of all networks in area ID 0.0.0.0, their
attached routers, and all area border routers.
backbone router
An OSPF router with all operational interfaces within area 0.0.0.0.
backplane
On an M40 router, component of the Packet Forwarding Engine that distributes
power, provides signal connectivity, manages shared memory on FPCs, and passes outgoing
data cells to FPCs. See also
flexible PIC concentrator (FPC)
.
backup
Denotes a Routing Engine in a dual Routing Engine chassis that is not currently controlling
the router’s operations.
backup designated router
An OSPF router on a broadcast segment that monitors the operation
of the designated router and takes over its functions in the event of a failure.
Glossary
537
bandwidth
The range of transmission frequencies a network can use, expressed as the difference
between the highest and lowest frequencies of a transmission channel. In computer networks,
greater bandwidth indicates faster data-transfer rate capacity.
base station controller (BSC)
Key network node in 3G systems that supervises the functioning
and control of multiple base transceiver stations.
base station subsystem (BSS)
Composed of the base transceiver station (BTS) and base station
controller (BSC).
Base Station System GPRS Protocol (BSSGP)
Processes routing and quality-of-service
(QoS) information for the BSS.
base transceiver station (BTS)
Mobile telephony equipment housed in cabinets and co-located
with antennas. Also known as a
radio base station
.
Bellcore
Bell Communications Research. Research and development organization created
after the divestiture of the Bell System. It is supported by the regional Bell holding companies
(RBHCs), which own the regional Bell operating companies (RBOCs).
Bellman-Ford algorithm
Algorithm used in distance-vector routing protocols to determine
the best path to all routes in the network.
bit error rate test (BERT)
A test that can be run on an electrical point-to-point interface (T1,
E1, T3, E3, etc.) to determine whether it is operating properly.
bit field match conditions
The use of fields in the header of an IP packet as match criteria in
a firewall filter.
bootstrap router
The single router in a multicast network responsible for distributing candidate
rendezvous point information to all PIM-enabled routers.
Border Gateway Protocol (BGP)
Exterior Gateway Protocol used to exchange routing information
among routers in different Autonomous Systems.
broadcast
Operation of sending network traffic from one network node to all other network
nodes.
Building Integrated Timing Source (BITS)
Dedicated timing source that synchronizes all
equipment in a particular building.
bundle
Collection of software that makes up a JUNOS software release.
C
call detail record (CDR)
A record containing data (such as origination, termination, length,
and time of day) unique to a specific call.
538
Glossary
candidate configuration
A file maintained by the JUNOS software containing all changes to
the router’s active configuration. It becomes the active configuration when a user issues the
commit
command.
candidate-RP-advertisements
Information sent by routers in a multicast network when they
are configured as a local rendezvous point. This information is unicast to the BSR for the multicast
domain.
CDMA2000
Radio transmission and backbone technology for the evolution to third-generation
(3G) mobile networks.
cell tax
Describes the physical transmission capacity used by header information when sending
data packets in an ATM network. Each ATM cell uses a 5-byte header.
CFM
Cubic feet per minute. Measure of air flow in volume per minute.
Challenge Handshake Authentication Protocol (CHAP)
A protocol that authenticates remote
users. CHAP is a server-driven, three-step authentication mechanism that depends on a shared
secret password that resides on both the server and the client.
channel service unit/data service unit (CSU/DSU)
The channel service unit connects a digital
phone line to a multiplexer or other digital signal device. The data service unit connects a
DTE to a digital phone line.
chassis daemon (chassisd)
JUNOS software process responsible for managing the interaction
of the router’s physical components.
circuit cross-connect (CCC)
A JUNOS software feature that allows you to configure transparent
connections between two circuits.
Cisco-RP-Announce
Message advertised into a multicast network by any router configured as
a local rendezvous point in an auto-RP network. It is advertised in a dense-mode fashion to the
224.0.1.39 multicast group address.
Cisco-RP-Discovery
Message advertised by the mapping agent in an auto-RP network. It contains
the rendezvous point to multicast group address assignments for the domain. It is advertised
in a dense-mode fashion to the 224.0.1.40 multicast group address.
class of service (CoS)
The method of classifying traffic on a packet-by-packet basis to provide
different service levels to different traffic. See also
type of service (ToS)
.
classless interdomain routing (CIDR)
A method of specifying Internet addresses in which
you explicitly specify the bits of the address to represent the network address instead of determining
this information from the first octet of the address.
client peer
In a BGP route reflection network, a member of a cluster that is not the route
reflector. See also
nonclient peer
.
Glossary
539
cluster
In BGP, a set of routers that have been grouped together. A cluster consists of at least
one system that acts as a route reflector, along with any number of client peers. The client peers
mainly receive their route information from the route reflector system. Routers in a cluster do
not need to be fully meshed.
Code Division Multiple Access (CDMA)
Technology for digital transmission of radio signals
between, for example, a mobile telephone and a base transceiver station (BTS).
command completion
Function of the router’s command-line interface that allows a user to
enter only the most significant characters in any command. Users access this function through
the spacebar or Tab key.
command-line interface (CLI)
The user’s interface to the JUNOS software through a console,
Telnet, or SSH session.
common language equipment identifier (CLEI)
Inventory code used to identify and track
telecommunications equipment.
community
In BGP, a group of destinations that share a common property. Community
information can be included as one of the path attributes in BGP update messages.
Competitive Local Exchange Carrier (CLEC)
(Pronounced “see-lek”) Company that competes
with the already established local telecommunications business by providing its own network
and switching.
complete sequence number PDU (CSNP)
Packet that contains a complete list of all the LSP
headers in the IS-IS database.
confederation
In BGP, a group of small Autonomous Systems that appears to external Autonomous
Systems to be a single Autonomous System.
configuration mode
JUNOS software mode allowing a user to alter the router’s current
configuration.
Connect
BGP neighbor state where the local router has initiated the TCP session and is
waiting for the remote peer to complete the TCP connection.
Connectionless Network Protocol (CLNP)
ISO-developed protocol for OSI connectionless
network service. CLNP is the OSI equivalent of IP.
Connector Interface Panel (CIP)
On an M40e or M160 router as well as on a T320 or T640
routing node the panel that contains connectors for the Routing Engines, BITS interfaces, and
alarm relay contacts.
constrained path
In traffic engineering, a path determined using the CSPF algorithm. The
ERO carried in the RSVP packets contains the constrained path information.
Constrained Shortest Path First (CSPF)
An MPLS algorithm that has been modified to take
into account specific restrictions when calculating the shortest path across the network.
540
Glossary
context-sensitive help
Function of the router’s command-line interface that allows a user to
request information on the JUNOS software command hierarchy. It is accessed in both operational
as well as configuration modes.
contributing routes
Active IP routes in the routing table that share the same most significant
bits and are more specific than an aggregate or generate route.
Control Board (CB)
On a T640 routing node, part of the host subsystem that provides control
and monitoring functions for router components.
core
The central backbone of the network.
craft interface
Mechanisms used by a Communication Workers of America craftsperson to
operate, administer, and maintain equipment or provision data communications. On a Juniper
Networks router, the craft interface allows you to view status and troubleshooting information
and perform system control functions.
customer edge device (CE device)
Router or switch in the customer’s network that is connected
to a service provider’s provider edge (PE) router and participates in a Layer 3 or Layer 2 VPN.
customer premises equipment (CPE) Telephone or other service provider equipment located
at a customer site.
Customized Application of Mobile Enhance Logic (CAMEL) ETSI standard for GSM networks
that enhances the provision of Intelligent Network services.
D
daemon Background process that performs operations on behalf of the system software and
hardware. Daemons normally start when the system software is booted, and they run as long
as the software is running. In the JUNOS software, daemons are also referred to as processes.
damping Method of reducing the number of update messages sent between BGP peers, thereby
reducing the load on these peers without adversely affecting the route convergence time for stable
routes. The protocol accomplishes this by not advertising unstable routes.
data circuit-terminating equipment (DCE) An RS-232-C device, typically used for a modem
or printer, or a network access and packet switching node.
data-link connection identifier (DLCI) Identifier for a Frame Relay virtual connection (also
called a logical interface).
data service unit (DSU) A device used to connect a DTE to a digital phone line. Converts digital
data from a router to voltages and encoding required by the phone line. See also channel service
unit/data service unit (CSU/DSU).
Data Terminal Equipment (DTE) The RS-232-C interface that a computer uses to exchange
information with a serial device.
Glossary 541
Database Description packet OSPF packet type used in the formation of an adjacency. It
sends summary information about the local router’s database to the neighboring router.
dcd The JUNOS software interface process, called the Device Control Daemon.
deactivate A method of modifying the router’s active configuration. Portions of the hierarchy
marked as inactive using this command are ignored during the router’s commit process as if they
were not configured at all.
dead interval The amount of time an OSPF router maintains a neighbor relationship before
declaring that neighbor as no longer operational. The JUNOS software uses a default value of
40 seconds for this timer.
default address Router address that is used as the source address on unnumbered interfaces.
default route Route used to forward IP packets when a more specific route is not present in the
routing table. Often represented as 0.0.0.0 /0, the default route is sometimes referred to as the
route of last resort.
denial of service (DoS) System security breach in which network services become unavailable
to users.
dense mode A method of forwarding multicast traffic to interested listeners. Dense mode forwarding
assumes that the majority of hosts on the network wish to receive the multicast data.
Routers flood packets and prune back unwanted traffic every 3 minutes.
dense wavelength-division multiplexing (DWDM) Technology that enables data from different
sources to be carried together on an optical fiber, with each signal carried on its own separate
wavelength.
designated router In OSPF, a router selected by other routers that is responsible for representing
the local segment to the remainder of the network, which reduces the amount of network
traffic and the size of the routers’ topological databases.
destination prefix length The number of bits used for the network portion of a CIDR IP
address.
Differentiated Services Codepoint (DSCP) The use of the first 6 bits of the IPv4 Type of Service
byte. The use of the DSCP for classifying traffic allows an administrator to have 64 unique
service levels in the network.
Diffie-Hellman A public key scheme, invented by Whitfield Diffie and Martin Hellman, used
for sharing a secret key without communicating secret information, thus precluding the need for
a secure channel. Once correspondents have computed the secret shared key, they can use it to
encrypt communications.
Diffserv Differentiated Service (based on RFC 2474). Diffserv uses the ToS byte to identify different
packet flows on a packet-by-packet basis. Diffserv adds a Class Selector Codepoint (CSCP)
and a Differentiated Services Codepoint (DSCP).
542 Glossary
Dijkstra algorithm See shortest path first (SPF).
direct routes See interface routes.
disable A method of modifying the router’s active configuration. Portions of the hierarchy
marked as disabled (mainly router interfaces) cause the router to use the configuration but stop
the pertinent operation of the configuration.
discard JUNOS software syntax command used in a routing policy or a firewall filter. It halts
the logical processing of the policy or filter when a set of match conditions is met. The specific
route or IP packet is dropped from the network silently. It may also be a next-hop attribute
assigned to a route in the routing table.
distance-vector Method used in Bellman-Ford routing protocols to determine the best path to
all routes in the network. Each router determines the distance (metric) to the destination as well
as the vector (next hop) to follow.
Distance Vector Multicast Routing Protocol (DVMRP) Distributed multicast routing protocol
that dynamically generates IP multicast delivery trees using a technique called reverse path
multicasting (RPM) to forward multicast traffic to downstream interfaces.
Distributed Buffer Manager ASICs Juniper Networks ASIC responsible for managing the
router’s packet storage memory.
Down OSPF adjacency state that is the starting state for the protocol.
drop profile Drop probabilities for different levels of buffer fullness that are used by RED to
determine if a packet is dropped from a queue or transmitted out an interface.
dual inline memory module (DIMM) A 168-pin memory module that supports 64-bit data
transfer.
Dynamic Host Configuration Protocol (DHCP) Allocates IP addresses dynamically so that
they can be reused when they are no longer needed.
dynamic label-switched path An MPLS network path established by signaling protocols
such as RSVP or LDP.
dynamic random access memory (DRAM) Storage source on the router that can be accessed
quickly by a process.
E
edge router In MPLS, a router located at the beginning or end of a label-switching tunnel.
When at the beginning of a tunnel, an edge router applies labels to new packets entering the
tunnel. When at the end of a tunnel, the edge router returns to forwarding the packets using the
destination IP address. See also Multiprotocol Label Switching (MPLS).
Glossary 543
editor macros (Emacs) Shortcut keystrokes used within the router’s command-line interface.
These macros move the cursor and delete characters based on the specific sequence specified.
egress router In MPLS, the last router in a label-switched path (LSP). See also ingress router.
electromagnetic interference (EMI) Any electromagnetic disturbance that interrupts, obstructs,
or otherwise degrades or limits the effective performance of electronics or electrical equipment.
Electronic Industries Association (EIA) A United States trade group that represents manufacturers
of electronics devices and sets standards and specifications.
embedded OS software Software used by a Juniper Networks router to operate the physical
router components.
encapsulating security payload (ESP) A fundamental component of IPSec-compliant VPNs,
ESP specifies an IP packet’s encryption, data integrity checks, and sender authentication, which
are added as a header to the IP packet. See also Authentication Header (AH).
end system In IS-IS, the network entity that sends and receives packets.
Equipment Identity Register (EIR) Mobile network database that contains information
about devices using the network.
Established BGP neighbor state that represents a fully functional BGP peering session.
exact JUNOS software routing policy match type that represents only the route specified in a
route filter.
exception packet An IP packet not processed by the normal packet flow through the Packet
Forwarding Engine. Exception packets include local delivery information, expired TTL packets,
or packets with an IP option specified.
Exchange OSPF adjacency state that means the two neighboring routers are actively sending
Database Description packets to each other to exchange their database contents.
Exchange Carriers Standards Association (ECSA) A standards organization created after
the divestiture of the Bell System to represent the interests of interexchange carriers.
explicit path See signaled path.
Explicit Route Object (ERO) Extension to RSVP that allows an RSVP Path message to traverse
an explicit sequence of routers that is independent of conventional shortest-path IP routing.
export To place routes from the routing table into a routing protocol.
ExStart OSPF adjacency state where the neighboring routers negotiate who is in charge of the
synchronization process.
Exterior Gateway Protocol (EGP) The original exterior gateway protocol used to exchange
routing information among routers in different Autonomous Systems. EGP was replaced by
BGP as the size and complexity of the Internet grew.
544 Glossary
External BGP (EBGP) BGP configuration in which sessions are established between routers in
different ASs.
external metric A cost included in a route when OSPF exports route information from
external Autonomous Systems. There are two types of external metrics: Type 1 and Type 2.
F
far-end alarm and control (FEAC) Signal used to send alarm or status information from the
far-end terminal back to the near-end terminal and to initiate loopbacks at the far-end terminal
from the near-end terminal.
fast reroute Mechanism for automatically rerouting traffic on an LSP if a node or link in an
LSP fails, thus reducing the loss of packets traveling over the LSP.
field-replaceable unit (FRU) Router component that customers can replace onsite.
firewall A security gateway positioned between two different networks, usually between a
trusted network and the Internet. A firewall ensures that all traffic that crosses it conforms to the
organization’s security policy. Firewalls track and control communications, deciding whether to
pass, reject, discard, encrypt, or log them. Firewalls also can be used to secure sensitive portions
of a local network.
first in, first out (FIFO) Queuing and buffering method where the first data packet stored in
the queue is the first data packet removed from the queue. All JUNOS software interface queues
operate in this mode by default.
flap damping See damping.
flapping See route flapping.
flexible PIC concentrator (FPC) An interface concentrator on which PICs are mounted. An
FPC inserts into a slot in a Juniper Networks router. See also physical interface card (PIC).
floating static route A route that should be used only when all dynamically learned versions
of that same route are no longer in the routing table.
flood and prune Method of forwarding multicast data packets in a dense-mode network.
This process repeats itself every 3 minutes.
flow control action JUNOS software syntax used in a routing policy or a firewall filter. It
alters the default logical processing of the policy or filter when a set of match conditions is met.
forwarding class Internal router designation that represents the queuing service offered to IP
packets matching some set of criteria. The forwarding class is assigned to a packet when it enters
the router and can be modified by a routing policy or a firewall filter.
Glossary 545
Forwarding Engine Board (FEB) In M5 and M10 routers, provides route lookup, filtering,
and switching to the destination port.
forwarding information base See forwarding table.
forwarding table JUNOS software forwarding information base (FIB). The JUNOS routing
protocol process installs active routes from its routing tables into the Routing Engine forwarding
table. The kernel copies this forwarding table into the Packet Forwarding Engine, which is responsible
for determining which interface transmits the packets.
Frame Relay Layer 2 encoding and addressing mechanism that uses a DLCI to segment logical
circuits on a physical transmission media.
from JUNOS software command syntax that contains match criteria in a routing policy or a
firewall filter.
Full OSPF adjacency state that represents a fully functional neighbor relationship.
fxp0 JUNOS software permanent interface used for out-of-band network access to the router.
fxp1 JUNOS software permanent interface used for communications between the Routing
Engine and the Packet Forwarding Engine.
fxp2 JUNOS software permanent interface used for communications between the Routing
Engine and the Packet Forwarding Engine. This interface is not present on all routers.
G
Garbage Collection timer Timer used in a distance-vector network that represents the time
remaining before a route is removed from the routing table.
Gateway GPRS Support Node (GGSN) Router that serves as a gateway between mobile networks
and packet data networks.
G-CDR GGSN call detail record. Collection of charges in ASN.1 format that is eventually
billed to a mobile station user.
General Packet Radio Service (GPRS) Packet-switched service that allows full mobility and
wide area coverage as information is sent and received across a mobile network.
generated route A summary route that uses an IP address next hop to forward packets in an
IP network. A generated route is functionally similar to an aggregated route.
Global System for Mobile Communications (GSM) A standard for mobile communications
networks that delivers high quality and secure mobile voice and data services with full roaming
capabilities across the world.
546 Glossary
GPRS Tunneling Protocol (GTP) Protocol that transports IP packets between an SGSN and
a GGSN.
GPRS Tunneling Protocol Control (GTP-C) Protocol that allows an SGSN to establish packet
data network access for a mobile station.
GPRS Tunneling Protocol User (GTP-U) Protocol that carries mobile station user data
packets.
group A collection of related BGP peers.
group address The IP address used as the destination address in a multicast IP packet. It functionally
represents the senders and interested receivers for a particular multicast data stream.
H
hash A one-way function that takes a message of any length and produces a fixed-length
digest. In security, a message digest is used to validate that the contents of a message have not
been altered in transit. The Secure Hash Algorithm (SHA-1) and Message Digest 5 (MD5) are
commonly used hashes.
Hashed Message Authentication Code (HMAC) A mechanism for message authentication
that uses cryptographic hash functions. HMAC can be used with any iterative cryptographic
hash function—for example, MD5 or SHA-1—in combination with a secret shared key. The
cryptographic strength of HMAC depends on the properties of the underlying hash function.
hello interval The amount of time an OSPF router sends a hello packet to each adjacent
neighbor. The JUNOS software uses a default value of 10 seconds for this timer.
hello mechanism Process used by an RSVP router to enhance the detection of network outages
in an MPLS network.
High-Level Data Link Control (HDLC) An International Telecommunication Union (ITU)
standard for a bit-oriented data link layer protocol on which most other bit-oriented protocols
are based.
High-Speed Circuit-Switched Data (HSCSC) Circuit-switched wireless data transmission for
mobile users, at data rates up to 38.4Kbps.
hold down A timer used by distance-vector protocols to prevent the propagation of incorrect
routing knowledge to other routers in the network.
hold time Maximum number of seconds allowed to elapse between the time a BGP system
receives successive keepalive or update messages from a peer.
Home Location Register (HLR) Database containing information about a subscriber and the
current location of a subscriber’s mobile station.
Glossary 547
Host Membership Query IGMP packet sent by a router to determine whether interested
receivers exist on a broadcast network for multicast traffic.
Host Membership Report IGMP packet sent by an interested receiver for a particular multicast
group address. Hosts send Report messages when they first join a group or in response to
a Query packet from the local router.
host module On an M160 router, provides routing and system management functions of the
router. Consists of the Routing Engine and Miscellaneous Control Subsystem (MCS).
host subsystem On a T640 routing node, provides routing and system-management functions
of the router. Consists of a Routing Engine and an adjacent Control Board (CB).
I
Idle The initial BGP neighbor state where the local router is refusing all incoming session
requests.
import To install routes from the routing protocols into a routing table.
inet.0 Default JUNOS software routing table for IPv4 unicast routes.
inet.1 Default JUNOS software routing table for storing the multicast cache for active data
streams in the network.
inet.2 Default JUNOS software routing table for storing unicast IPv4 routes specifically used
to prevent forwarding loops in a multicast network.
inet.3 Default JUNOS software routing table for storing the egress IP address of an MPLS
label-switched path.
inet.4 Default JUNOS software routing table for storing information generated by the Multicast
Source Discovery Protocol (MSDP).
inet6.0 Default JUNOS software routing table for storing unicast IPv6 routes.
infinity metric A metric value used in distance-vector protocols to represent an unusable
route. For RIP, the infinity metric is 16.
ingress router In MPLS, the first router in a label-switched path (LSP). See also egress router.
init OSPF adjacency state where the local router has received a hello packet but bidirectional
communication is not yet established.
insert JUNOS software command that allows a user to reorder terms in a routing policy or
a firewall filter. It may also be used to change the order of a policy chain.
Institute of Electronic and Electrical Engineers (IEEE) The international professional
society for electrical engineers that sets standards for networking technologies.
548 Glossary
Integrated Drive Electronics (IDE) Type of hard disk on the Routing Engine.
inter-AS routing Routing of packets among different ASs. See also External BGP (EBGP).
intercluster reflection In a BGP route reflection network, the redistribution of routing information
by a route reflector system to all nonclient peers (BGP peers not in the cluster). See also route
reflection.
interface cost Value added to all received routes in a distance-vector network before placing
them into the routing table. The JUNOS software uses a cost of 1 for this value.
interface routes Routes that are in the routing table because an interface has been configured
with an IP address. Also called direct and local routes.
Interior Gateway Protocol (IGP) A routing protocol designed to operate within the confines
of an administrative domain. Examples include the Routing Information Protocol (RIP), Open
Shortest Path First (OSPF), and Intermediate System to Intermediate System (IS-IS).
intermediate system In IS-IS, the network entity that sends and receives packets and that can
also route packets.
Intermediate System-to-Intermediate System (IS-IS) Link-state, interior gateway routing
protocol for IP networks that also uses the shortest path first (SPF) algorithm to determine
routes.
Internal BGP (IBGP) BGP configuration in which sessions are established between routers in
the same AS.
Internal Ethernet Another name for the fxp1 and fxp2 interfaces that provide communications
between the Routing Engine and the Packet Forwarding Engine.
International Electrotechnical Commission (IEC) See International Organization for Standardization
(ISO).
International Mobile Station Equipment Identity (IMEI) A unique code used to identify an
individual mobile station to a GSM network.
International Mobile Subscriber Identity (IMSI) Information that identifies a particular subscriber
to a GSM network.
International Organization for Standardization (ISO) Worldwide federation of standards
bodies that promotes international standardization and publishes international agreements as
International Standards.
International Telecommunications Union (ITU) Formerly known as the CCITT, group supported
by the United Nations that makes recommendations and coordinates the development
of telecommunications standards for the entire world.
Internet Assigned Numbers Authority (IANA) Regulatory group that maintains all assigned
and registered Internet numbers, such as IP and multicast addresses.
Glossary 549
Internet Control Message Protocol (ICMP) Used in router discovery, ICMP allows router
advertisements that enable a host to discover addresses of operating routers on the subnet.
Internet Engineering Task Force (IETF) International community of network designers,
operators, vendors, and researchers concerned with the evolution of the Internet architecture
and the smooth operation of the Internet.
Internet Group Management Protocol (IGMP) Multicast protocol used for router-to-host
communications. Hosts use IGMP to request multicast data streams from the network. Routers
use IGMP to determine whether group members are still present on the local segment.
Internet Key Exchange (IKE) The key management protocol used in IPSec, IKE combines the
ISAKMP and Oakley protocols to create encryption keys and security associations.
Internet Processor ASIC Juniper Networks ASIC responsible for using the forwarding table
to make routing decisions within the Packet Forwarding Engine. The Internet Processor ASIC
also implements firewall filters.
Internet Protocol (IP) The protocol used for sending data from one point to another on the
Internet.
Internet Protocol Security (IPSec) The industry standard for establishing VPNs, IPSec comprises
a group of protocols and algorithms that provide authentication and encryption of data
across IP-based networks.
Internet Security Association and Key Management Protocol (ISAKMP) A protocol that
allows the receiver of a message to obtain a public key and use digital certificates to authenticate
the sender’s identity. ISAKMP is designed to be key exchange independent; that is, it supports
many different key exchanges. See also Internet Key Exchange (IKE) and Oakley.
Internet service provider (ISP) Company that provides access to the Internet and related
services.
intra-AS routing The routing of packets within a single AS. See also Internal BGP (IBGP).
I/O Manager ASIC Juniper Networks ASIC responsible for segmenting data packets into
64-byte J-cells and for queuing result cells prior to transmission.
J
jbase JUNOS software package containing updates to the kernel.
jbundle JUNOS software package containing all possible software package files.
J-cell A 64-byte data unit used within the Packet Forwarding Engine. All IP packets processed
by a Juniper Networks router are segmented into J-cells.
jdocs JUNOS software package containing the documentation set.
550 Glossary
jitter Small random variation introduced into the value of a timer to prevent multiple timer
expirations from becoming synchronized.
jkernel JUNOS software package containing the basic components of the software.
Join message PIM message sent hop-by-hop upstream towards a multicast source or the RP
of the domain. It requests that multicast traffic be sent downstream to the router originating the
message.
jpfe JUNOS software package containing the Embedded OS software for operating the Packet
Forwarding Engine.
jroute JUNOS software package containing the software used by the Routing Engine.
K
keepalive BGP packet used to maintain a peering session with a neighbor.
kernel The basic software component of the JUNOS software. It operates the various daemons
used to control the router’s operations.
kernel forwarding table See forwarding table.
L
label In MPLS, a 20-bit unsigned integer in the range 0 through 1048575, used to identify a
packet traveling along an LSP.
Label Distribution Protocol (LDP) A signaling protocol used to establish an MPLS labelswitched
path. LDP uses the IGP shortest-path cost to each egress router in the network and is
not capable of utilizing traffic-engineering concepts.
label object An RSVP message object that contains the label value allocated by the next
downstream router.
label pop operation Function performed by an MPLS router in which the top label in a label
stack is removed from the data packet.
label push operation Function performed by an MPLS router in which a new label is added
to the top of the data packet.
label request object An RSVP message object that requests each router along the path of an
LSP to allocate a label for forwarding purposes.
label swap operation Function performed by an MPLS router in which the top label in a label
stack is replaced with a new label before forwarding the data packet to the next-hop router.
Glossary 551
label-switched path (LSP) Sequence of routers that cooperatively perform MPLS operations
for a packet stream. The first router in an LSP is called the ingress router, and the last router in
the path is called the egress router. An LSP is a point-to-point, simplex connection from the
ingress router to the egress router. (The ingress and egress routers cannot be the same router.)
label switching See Multiprotocol Label Switching (MPLS).
label-switching router (LSR) A router on which MPLS is enabled and is thus capable of processing
label-switched packets.
label values A 20-bit field in an MPLS header used by routers to forward data traffic along
an MPLS label-switched path.
Lightweight Directory Access Protocol (LDAP) Software protocol used for locating
resources on a public or private network.
line loopback A method used to troubleshoot a problem with a physical transmission media.
A transmission device in the network sends the data signal back to the originating router.
link Communication path between two neighbors. A link is up when communication is possible
between the two end points.
link-state acknowledgment OSPF data packet used to inform a neighbor that a link-state
update packet has been successfully received.
link-state advertisement (LSA) OSPF data structure that is advertised in a link-state update
packet. Each LSA uniquely describes a portion of the OSPF network.
link-state database All routing knowledge in a link-state network is contained in this database.
Each router runs the SPF algorithm against this database to locate the best network path
to each destination in the network.
link-state PDU (LSP) Packets that contain information about the state of adjacencies to neighboring
systems in an IS-IS network.
link-state request list A list generated by an OSPF router during the exchange of database
information while forming an adjacency. Advertised information by a neighbor that the local
router doesn’t contain is placed onto this list.
link-state request packet OSPF data packet that a router uses to request database information
from a neighboring router.
link-state update OSPF data packet that contains one or multiple LSAs. It is used to advertise
routing knowledge into the network.
loading OSPF adjacency state where the local router is sending link-state request packets to
its neighbor and is awaiting the appropriate link-state updates from that neighbor.
local preference Optional BGP path attribute carried in internal BGP update packets that
indicates the degree of preference for an external route.
552 Glossary
local significance Concept used in an MPLS network where the label values are unique only
between two neighbor routers.
Local-RIB Logical software table that contains BGP routes used by the local router to forward
data packets.
logical operator Characters used in a firewall filter to represent a Boolean AND or OR
operation.
longer JUNOS software routing policy match type that represents all routes more specific
than the given subnet, but not the given subnet itself. It is similar to a mathematical greater-than
operation.
loose In the context of traffic engineering, a path that can use any route or any number of
other intermediate (transit) points to reach the next address in the path. (Definition from RFC
791, modified to fit LSPs.)
loose hop Router in an MPLS named-path that is not required to be directly connected to the
local router.
M
management daemon (mgd) JUNOS software process responsible for managing all user
access to the router.
Management Ethernet Another name for the fxp0 interface that provides out-of-band access
to the router.
Management Information Base (MIB) Definition of an object that can be managed by SNMP.
mapping agent A router used in an auto-RP multicast network to select the rendezvous point
for all multicast group addresses. This information is then advertised to all other routers in the
domain.
Martian address Network address about which all information is ignored.
Martian routes Network routes about which information is ignored. The JUNOS software
doesn’t allow Martian routes to reside in the inet.0 routing table.
mask See subnet mask.
master The router in control of the OSPF database exchange during an adjacency formation.
match A logical concept used in a routing policy or a firewall filter. It denotes the criteria used
to find a route or IP packet before performing some action.
match type JUNOS software syntax used in a route filter to better describe the routes that
should match the policy term.
Glossary 553
maximum transmission unit (MTU) Limit on segment size for a network.
MBone Internet multicast backbone. An interconnected set of subnetworks and routers that
support the delivery of IP multicast traffic. The MBone is a virtual network that is layered on
top of sections of the physical Internet.
mean time between failure (MTBF) Measure of hardware component reliability.
mesh Network topology in which devices are organized in a manageable, segmented manner
with many, often redundant, interconnections between network nodes.
message aggregation An extension to the RSVP specification that allows neighboring
routers to bundle up to 30 RSVP messages into a single protocol packet.
Message Digest 5 (MD5) A one-way hashing algorithm that produces a 128-bit hash. See also
Secure Hash Algorithm (SHA-1).
midplane Forms the rear of the PIC cage on M5 and M10 routers and the FPC card cage on
M20, M40e, M160, and T640 platforms. Provides data transfer, power distribution, and signal
connectivity.
Miscellaneous Control Subsystem (MCS) On the M40e and M160 routers, provides control
and monitoring functions for router components and SONET clocking for the router.
mobile network access subsystem (MAS) GSN application subsystem that contains the
access server.
mobile point-to-point control subsystem (MPS) GSN application subsystem that controls
all functionality associated with a particular connection.
mobile station A mobile device, such as a cellular phone or a mobile personal digital assistant
(PDA).
Mobile Station Integrated Services Digital Network Number (MSISDN) Number that
callers use to reach a mobile services subscriber.
Mobile Switching Center (MSC) Provides origination and termination functions to calls
from a mobile station user.
mobile transport subsystem (MTS) GSN application subsystem that implements all the protocols
used by the GSN.
multicast Operation of sending network traffic from one network node to multiple network
nodes.
multicast distribution tree The data path between the sender (host) and the multicast group
members (receiver or listener).
Multiple Exit Discriminator (MED) Optional BGP path attribute consisting of a metric value
that is used to determine the exit point to a destination when all other factors in determining the
exit point are equal.
554 Glossary
Multiprotocol BGP (MBGP) An extension to BGP that allows you to exchange routing knowledge
from multiple NLRI within and between BGP ASs.
Multiprotocol Label Switching (MPLS) Mechanism for engineering network traffic patterns
that functions by assigning to network packets short labels that describe how to forward them
through the network. Also called label switching. See also traffic engineering.
N
named-path JUNOS software syntax that specifies a portion or the entire network path that
should be used as a constraint in signaling an MPLS label-switched path.
neighbor Adjacent system reachable by traversing a single subnetwork. An immediately adjacent
router. A system to which a BGP session is established. Also called a peer.
network entity title (NET) Network address defined by the ISO network architecture and
used in CLNS-based networks.
network layer reachability information (NLRI) Information that is carried in BGP packets
and is used by MBGP.
network-link advertisement An OSPF link-state advertisement flooded throughout a single
area by designated routers to describe all routers attached to the DR’s local segment.
network LSA OSPF link-state advertisement sent by the DR on a broadcast or NBMA segment.
It advertises the subnet associated with the DR’s segment.
network service access point (NSAP) Connection to a network that is identified by a network
address.
Network Summary LSA OSPF link-state advertisement sent by an ABR to advertise internal
OSPF routing knowledge across an area boundary.
Network Time Protocol (NTP) Protocol used to synchronize computer clock times on a
network.
Next Hop BGP attribute that specifies the router to send packets to for a particular set of
routes.
nonclient peer In a BGP route reflection network, a BGP peer that is not a member of a
cluster. See also client peer.
notification cell JUNOS software data structure generated by the Distributed Buffer Manager
ASIC that represents the header contents of an IP packet. The Internet Processor ASIC uses the
notification cell to perform a forwarding table lookup.
Notification message BGP message that informs a neighbor about an error condition and
then possibly terminates the BGP peering session.
Glossary 555
not-so-stubby area (NSSA) In OSPF, a type of stub area in which external routes can be
flooded.
n-selector Last byte of an ISO Network Entity Title (NET) address.
Null Register message A PIM message sent by the first hop router to the RP. It informs the
RP that the local source is still actively sending multicast packets into the network should future
interested listeners send a Join message to the RP.
numeric range match conditions The use of numeric values (protocol and port numbers) in
the header of an IP packet as match criteria in a firewall filter.
O
Oakley A key determination protocol based on the Diffie-Hellman algorithm that provides
added security, including authentication. Oakley was the key-exchange algorithm mandated for
use with the initial version of ISAKMP, although various algorithms can be used. Oakley
describes a series of key exchanges called “modes” and details the services provided by each; for
example, Perfect Forward Secrecy for keys, identity protection, and authentication. See also
Internet Security Association and Key Management Protocol (ISAKMP).
Open message BGP message that allows two neighbors to negotiate the parameters of the
peering session.
OpenConfirm BGP neighbor state that shows a valid Open message was received from the
remote peer.
OpenSent BGP neighbor state that shows an Open message was sent to the remote peer and
the local router is waiting for an Open message to be returned.
Open Shortest Path First (OSPF) A link-state IGP that makes routing decisions based on the
shortest path first (SPF) algorithm (also referred to as the Dijkstra algorithm).
Open System Interconnection (OSI) Standard reference model for how messages are transmitted
between two points on a network.
operational mode JUNOS software mode allowing a user to view statistics and information
concerning the router’s current operating status.
Optical Carrier (OC) In SONET, Optical Carrier levels indicate the transmission rate of digital
signals on optical fiber.
Origin BGP attribute that describes the believability of a particular route. The router that first
places the route into BGP should attempt to accurately describe the source of the route.
orlonger JUNOS software routing policy match type that represents all routes more specific
than the given subnet, including the given subnet itself. It is similar to a mathematical
greater-than-or-equals-to operation.
556 Glossary
OSPF Hello packet Message sent by each OSPF router to each adjacent neighbor. It is used to
establish and maintain the router’s neighbor relationships.
overlay network Network design seen where a logical Layer 3 topology (IP subnets) is operating
over a logical Layer 2 topology (ATM PVCs). Layers in the network do not have knowledge
of each other, and each requires separate management and operation.
P
package A collection of files that make up a JUNOS software component.
packet data protocol (PDP) Network protocol, such as IP, used by packet data networks connected
to a GPRS network.
Packet Forwarding Engine The architectural portion of the router that processes packets by
forwarding them between input and output interfaces.
Packet Loss Priority (PLP) Internal router designation that represents a greater probability of
dropping a particular IP packet based on configured class of service settings. The priority is
assigned to a packet when it enters the router and can be modified by a firewall filter.
partial sequence number PDU (PSNP) Packet that contains only a partial list of the LSP
headers in the IS-IS link-state database.
path attribute Information about a BGP route, such as the route origin, AS path, and nexthop
router.
PathErr RSVP message that indicates an error has occurred along an established LSP. The
message is advertised upstream toward the ingress router and it doesn’t remove any RSVP soft
state from the network.
PathTear Message RSVP message that indicates the established LSP and its associated soft
state should be removed by the network. The message is advertised downstream hop-by-hop
toward the egress router.
path-vector protocol A routing protocol definition that describes the direction to the destination
and the network path used to reach the destination. This often describes the functionality
of BGP.
peer An immediately adjacent router with which a protocol relationship has been established.
Also called a neighbor.
penultimate hop popping (PHP) A mechanism used in an MPLS network that allows the
transit router prior to the egress to perform a label pop operation and forward the remaining
data (often a native IPv4 packet) to the egress router.
penultimate router The last transit router prior to the egress router in an MPLS labelswitched
path.
Glossary 557
Perfect Forward Secrecy (PFS) A condition derived from an encryption system that changes
encryption keys often and ensures that no two sets of keys have any relation to each other. The
advantage of PFS is that if one set of keys is compromised, only communications using those
keys are at risk. An example of a system that uses PFS is Diffie-Hellman.
Peripheral Component Interconnect (PCI) Standard, high-speed bus for connecting computer
peripherals. Used on the Routing Engine.
permanent virtual circuit (PVC) A logical Layer 2 connection between two network
devices. The network path is preengineered and configured on each device in the network
supporting the PVC.
Personal Computer Memory Card International Association (PCMCIA) Industry group
that promotes standards for credit card–size memory or I/O devices.
Physical Interface Card (PIC) A network interface–specific card that can be installed on a FPC
in the router.
PIC I/O Manager ASIC Juniper Networks ASIC responsible for receiving and transmitting
information on the physical media. It performs media-specific tasks within the Packet Forwarding
Engine.
PLP bit Packet Loss Priority bit. Used to identify packets that have experienced congestion or
are from a transmission that exceeded a service provider’s customer service license agreement.
This bit can be used as part of a router’s congestion control mechanism and can be set by the
interface or by a filter.
policing Applying rate limits on bandwidth and burst size for traffic on a particular interface
or IPv4 prefix.
Policing Equivalence Classes (PEC) In traffic policing, a set of packets that is treated the
same by the packet classifier.
pop Removal of the last label, by a router, from a packet as it exits an MPLS domain.
Point-to-Point Protocol (PPP) Link-layer protocol that provides multiprotocol encapsulation.
It is used for link-layer and network-layer configuration.
poison reverse Method used in distance-vector networks to avoid routing loops. Each router
advertises routes back to the neighbor it received them from with an infinity metric assigned.
policy chain The application of multiple routing policies in a single location. The policies are
evaluated in a predefined manner and are always followed by the default policy for the specific
application location.
precedence bits The first three bits in the ToS byte. On a Juniper Networks router, these bits
are used to sort or classify individual packets as they arrive at an interface. The classification
determines the forwarding class to which the packet is directed upon transmission.
558 Glossary
preference Desirability of a route to become the active route. A route with a lower preference
value is more likely to become the active route. The preference is an arbitrary value in the range
0 through 4,294,967,295 that the routing protocol process uses to rank routes received from
different protocols, interfaces, or remote systems.
preferred address On an interface, the default local address used for packets sourced by the
local router to destinations on the subnet.
prefix-length-range JUNOS software routing policy match type representing all routes that
share the same most significant bits. The prefix length of the route must also lie between the two
supplied lengths in the route filter.
primary address On an interface, the address used by default as the local address for broadcast
and multicast packets sourced locally and sent out the interface.
primary contributing route The contributing route with the numerically smallest prefix and
smallest JUNOS software preference value. This route is the default next hop used for a generated
route.
primary interface Router interface that packets go out when no interface name is specified
and when the destination address does not imply a particular outgoing interface.
protocol address The logical Layer 3 address assigned to an interface within the JUNOS software.
protocol data unit (PDU) The basic data structure used by the IS-IS routing protocol to form
adjacencies and exchange routing information.
protocol families The grouping of logical properties within an interface configuration. The
JUNOS software supports the inet, iso, mpls, and inet6 families.
Protocol Independent Multicast (PIM) A protocol-independent multicast routing protocol.
PIM sparse mode routes to multicast groups that might span wide-area and interdomain internets.
PIM dense mode is a flood-and-prune protocol.
protocol preference A 32-bit value assigned to all routes placed into the routing table. It is
used as a tiebreaker when multiple exact routes are placed into the table by different protocols.
provider edge (PE) router A router in the service provider’s network that can have customer
edge (CE) devices connected and that participates in a virtual private network (VPN).
provider router Router in the service provider’s network that does not attach to a customer
edge (CE) device.
Prune message PIM message sent upstream to a multicast source or the RP of the domain. It
requests that multicast traffic stop being transmitted to the router originating the message.
public land mobile network (PLMN) A telecommunications network for mobile stations.
push Addition of a label or stack of labels, by a router, to a packet as it enters an MPLS
domain.
Glossary 559
Q
quad-wide A type of PIC that combines the PIC and the FPC within a single FPC slot.
qualified next hop A next hop for a static route that allows a second next hop for the same
static route to have different metric and preference properties than the original.
quality of service (QoS) Performance, such as transmission rates and error rates, of a communications
channel or system.
querier router PIM router on a broadcast subnet responsible for generating IGMP Query
messages for the segment.
R
radio frequency interference (RFI) Interference from high-frequency electromagnetic waves
emanating from electronic devices.
radio network controller (RNC) Manages the radio part of the network in UMTS.
Random Early Detection (RED) Gradual drop profile for a given class that is used for congestion
avoidance. RED tries to anticipate incipient congestion and reacts by dropping a small percentage
of packets from the head of the queue to ensure that a queue never becomes full.
rate limiting See policing.
rate policing See policing.
receive A next hop for a static route that allows all matching packets to be sent to the Routing
Engine for processing.
record route object (RRO) An RSVP message object that notes the IP address of each router
along the path of an LSP.
recursive lookup A method of consulting the routing table to locate the actual physical next
hop for a route when the supplied next hop is not directly connected.
regional Bell operating company (RBOC) (Pronounced “are-bock”) Regional telephone
companies formed as a result of the divestiture of the Bell System.
Register message PIM message unicast by the first hop router to the RP that contains the
multicast packets from the source encapsulated within its data field.
Register Stop message PIM message sent by the RP to the first hop router to halt the sending
of encapsulated multicast packets.
reject A next hop for a configured route that drops all matching packets from the network and
returns an ICMP message to the source IP address. Also used as an action in a routing policy or
a firewall filter.
560 Glossary
Remote Authentication Dial-In User Service (RADIUS) Authentication method for validating
users who attempt to access the router using Telnet.
rename JUNOS software command that allows a user to change the name of a routing policy,
a firewall filter, or any other variable character string defined in the router’s configuration.
Request for Comments (RFC) Internet standard specifications published by the Internet
Engineering Task Force.
Rendezvous Point (RP) For PIM-SM, a router acting as the root of the shared distribution tree.
Request message RIP message used by a router to ask for all or part of the routing table from
a neighbor.
resolve A next hop for a static route that allows the router to perform a recursive lookup to
locate the physical next hop for the route.
Resource Reservation Protocol (RSVP) Resource reservation setup protocol designed to
interact with integrated services on the Internet.
Response message RIP message used to advertise routing information into a network.
result cell JUNOS software data structure generated by the Internet Processor ASIC after performing
a forwarding table lookup.
ResvConf message RSVP message that allows the egress router to receive an explicit confirmation
message from a neighbor that its Resv message was received.
ResvErr message RSVP message that indicates an error has occurred along an established
LSP. The message is advertised downstream toward the egress router and it doesn’t remove any
RSVP soft state from the network.
ResvTear message RSVP message that indicates the established LSP and its associated soft
state should be removed by the network. The message is advertised upstream toward the ingress
router.
reverse path forwarding Method used in a multicast routing domain to prevent forwarding
loops.
reverse path multicasting (RPM) Routing algorithm used by DVMRP to forward multicast
traffic.
route filter JUNOS software syntax used in a routing policy to match an individual route or
a group of routes.
route flapping Situation in which BGP systems send an excessive number of update messages
to advertise and withdraw reachability of the same NLRI.
route identifier IP address of the router from which a BGP, IGP, or OSPF packet originated.
Glossary 561
route redistribution A method of placing learned routes from one protocol into another protocol
operating on the same router. The JUNOS software accomplishes this with a routing policy.
route reflection In BGP, configuring a group of routers into a cluster and having one system
act as a route reflector, redistributing routes from outside the cluster to all routers in the cluster.
Routers in a cluster do not need to be fully meshed.
Router ID An IP address used by a router to uniquely identify itself to a routing protocol. This
address may or may not be equal to a configured interface address.
router-link advertisement OSPF link-state advertisement flooded throughout a single area
by all routers to describe the state and cost of the router’s links to the area.
router LSA OSPF link-state advertisement sent by each router in the network. It describes the
local router’s connected subnets as well as their metric values.
Router Priority A numerical value assigned to an OSPF or an IS-IS interface that is used as the
first criterion in electing the designated router or designated intermediate system, respectively.
routing domain See Autonomous System (AS).
Routing Engine Architectural portion of the router that handles all routing protocol processes,
as well as other software processes that control the router’s interfaces, some of the
chassis components, system management, and user access to the router.
Routing Information Base (RIB) A logical data structure used by BGP to store routing
information.
Routing Information Protocol (RIP) Distance-vector Interior Gateway Protocol that makes
routing decisions based on hop count.
routing instance A collection of routing tables, interfaces, and routing protocol parameters.
The set of interfaces belongs to the routing tables and the routing protocol parameters control
the information in the routing tables.
routing protocol daemon (rpd) JUNOS software routing protocol process (daemon). Userlevel
background process responsible for starting, managing, and stopping the routing protocols
on a Juniper Networks router.
routing table Common database of routes learned from one or more routing protocols. All
routes are maintained by the JUNOS routing protocol process.
RSVP Path message RSVP message sent by the ingress router downstream toward the egress
router. It begins the establishment of a soft state database for a particular label-switched path.
RSVP Resv message RSVP message sent by the egress router upstream toward the ingress
router. It completes the establishment of the soft state database for a particular label-switched path.
RSVP signaled LSP A label-switched path that is dynamically established using RSVP Path
and Resv messages.
562 Glossary
S
Secure Hash Algorithm (SHA-1) A widely used hash function for use with Digital Signal
Standard (DSS). SHA-1 is more secure than MD5.
secure shell (SSH) A protocol that provides a secured method of logging in to a remote network
system.
security association (SA) An IPSec term that describes an agreement between two parties
about what rules to use for authentication and encryption algorithms, key exchange mechanisms,
and secure communications.
Security Parameter Index (SPI) A portion of the IPSec Authentication Header that communicates
which security protocols, such as authentication and encryption, are used for each packet in
a VPN connection.
segmentation and reassembly (SAR) Method used in ATM to transform IP packets into
ATM cells and cells into IP packets.
Serving GPRS Support Node (SGSN) Device in the mobile network that requests PDP contexts
with a GGSN.
Session Announcement Protocol (SAP) Used with multicast protocols to handle session
conference announcements.
session attribute object RSVP message object that is used to control the priority, preemption,
affinity class, and local rerouting of the LSP.
Session Description Protocol (SDP) Used with multicast protocols to handle session conference
announcements.
shared tree The multicast forwarding tree established from the RP to the last hop router for
a particular group address.
shim header The name used to describe the location of the MPLS header in a data packet. The
JUNOS software always places (shims) the header between the existing Layers 2 and 3 headers.
Short Message Service (SMS) GSM service that enables short text messages to be sent to and
from mobile telephones.
shortest path first (SPF) An algorithm used by IS-IS and OSPF to make routing decisions
based on the state of network links. Also called the Dijkstra algorithm.
shortest-path tree The multicast forwarding tree established from the first hop router to the
last hop router for a particular group address.
show route advertising-protocol JUNOS software command that displays the routes sent to
a neighbor for a particular protocol.
show route receive-protocol JUNOS software command that displays the routes received
from a neighbor for a particular protocol.
Glossary 563
signaled path In traffic engineering, an explicit path; that is, a path determined using RSVP
signaling. The ERO carried in the packets contains the explicit path information.
Signaling System 7 (SS7) Protocol used in telecommunications for delivering calls and services.
Simple Network Management Protocol (SNMP) Protocol governing network management
and the monitoring of network devices and their functions.
simplex interface An interface that assumes that packets it receives from itself are the result
of a software loopback process. The interface does not consider these packets when determining
whether the interface is functional.
soft state A database structure maintained by an RSVP router to store information about a
particular label-switched path.
SONET Clock Generator (SCG) On a M40e or M160 router as well as on a T320 or T640
routing node, the SCG provides Stratum 3 clock signal for the SONET/SDH interfaces. It also
provides external clock inputs.
source-based tree The multicast forwarding tree established from the source of traffic to all
interested receivers for a particular group address. It is often seen in a dense-mode forwarding
environment.
source-specific multicasting As part of the IGMPv3 specification, it allows an end host to
request multicast traffic for a group address from a specific source of traffic.
sparse mode A method of operating a multicast domain where sources of traffic and interested
receivers meet at a central rendezvous point. A sparse-mode network assumes that there
are very few receivers for each group address.
Split Horizon Method used in distance-vector networks to avoid routing loops. Each router
does not advertise routes back to the neighbor it received them from.
static label-switched path (static LSP) See static path.
static path In the context of traffic engineering, a static route that requires hop-by-hop manual
configuration. No signaling is used to create or maintain the path. Also called a static LSP.
static route A configured route that includes a route and a next hop. It is always present in
the routing table and doesn’t react to topology changes in the network.
static RP One of three methods of learning the rendezvous point to group address mapping
in a multicast network. Each router in the domain must be configured with the required RP
information.
strict In the context of traffic engineering, a route that must go directly to the next address in
the path. (Definition from RFC 791, modified to fit LSPs.)
strict hop Routers in an MPLS named path that are required to be directly connected to the
previous router in the configured path.
564 Glossary
Strict Priority Queuing (SPQ) Dequeuing method that provides a special queue that is serviced
until it is empty. The traffic sent to this queue tends to maintain a lower latency and
more consistent latency numbers than traffic sent to other queues. See also Alternate Priority
Queuing (APQ).
stub area In OSPF, an area through which, or into which, AS external advertisements are not
flooded.
subnet mask The number of bits of the network address used for the network portion of a
Class A, Class B, or Class C IP address.
summary-link advertisement OSPF link-statement advertisement flooded throughout the
advertisement’s associated areas by area border routers to describe the routes that they know
about in other areas.
Switch Interface Board (SIB) On a T320 or T640 routing node, provides the switching function
to the destination Packet Forwarding Engine.
Switching and Forwarding Module (SFM) On an M40e or M160 router, a component of the
Packet Forwarding Engine that provides route lookup, filtering, and switching to FPCs.
Synchronous Digital Hierarchy (SDH) CCITT variation of SONET standard.
Synchronous Optical Network (SONET) High-speed synchronous network specification
developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block
of SONET. Approved as an international standard in 1988. See also Synchronous Digital Hierarchy
(SDH).
Synchronous Transport Module (STM) CCITT specification for SONET at 155.52Mbps.
Synchronous Transport Signal (STS) Level 1 Basic building block signal of SONET, operating
at 51.84Mbps. Faster SONET rates are defined as STS-n, where n is a multiple of 51.84Mbps. See
also Synchronous Optical Network (SONET).
sysid System identifier. A portion of the ISO Network Entity Title (NET) address. The sysid
can be any 6 bytes that are unique throughout a domain.
syslog A method for storing messages to a file for troubleshooting or record-keeping purposes.
It can also be used as an action within a firewall filter to store information to the messages file.
System Control Board (SCB) On an M40 router, the part of the Packet Forwarding Engine
that performs route lookups, monitors system components, and controls FPC resets.
System Switching Board (SSB) On an M20 router, Packet Forwarding Engine component
that performs route lookups and component monitoring and monitors FPC operation.
Glossary 565
T
TCP port 179 The well-known port number used by BGP to establish a peering session with
a neighbor.
tcpdump A Unix packet monitoring utility used by the JUNOS software to view information
about packets sent or received by the Routing Engine.
Terminal Access Controller Access Control System Plus (TACACS+) Authentication
method for validating users who attempt to access the router.
terminating action An action in a routing policy or firewall filter that halts the logical software
processing of the policy or filter.
terms Used in a routing policy or firewall filter to segment the policy or filter into smaller
match and action pairs.
through JUNOS software routing policy match type representing all routes that fall between
the two supplied prefixes in the route filter.
Timeout timer Used in a distance-vector protocol to ensure the current route is still usable for
forwarding traffic. The JUNOS software uses a default value of 120 seconds.
token-bucket algorithm Used in a rate-policing application to enforce an average bandwidth
while allowing bursts of traffic up to a configured maximum value.
totally stubby area An OSPF area type that prevents Type 3, 4, and 5 LSAs from entering the
non-backbone area.
traffic engineering Process of selecting the paths chosen by data traffic in order to balance the
traffic load on the various links, routers, and switches in the network. (Definition from http://
www.ietf.org/internet-drafts/draft-ietf-mpls-framework-04.txt.) See also Multiprotocol
Label Switching (MPLS).
transient interfaces Interfaces that can be moved from one location in the router to another.
All customer-facing interfaces are considered transient in nature.
transit area In OSPF, an area used to pass traffic from one adjacent area to the backbone or
to another area if the backbone is more than two hops away from an area.
transit router In MPLS, any intermediate router in the LSP between the ingress router and the
egress router.
Transmission Control Protocol (TCP) Works in conjunction with Internet Protocol (IP) to
send data over the Internet. Divides a message into packets and tracks the packets from the
point of origin.
566 Glossary
transport mode An IPSec mode of operation in which the data payload is encrypted but the
original IP header is left untouched. The IP addresses of the source or destination can be modified
if the packet is intercepted. Because of its construction, transport mode can be used only
when the communication endpoint and cryptographic endpoint are the same. VPN gateways
that provide encryption and decryption services for protected hosts cannot use transport mode
for protected VPN communications. See also tunnel mode.
triggered updates Used in a distance-vector protocol to reduce the time for the network to
converge. When a router has a topology change, it immediately sends the information to its
neighbors instead of waiting for a timer to expire.
Triple-DES A 168-bit encryption algorithm that encrypts data blocks with three different keys
in succession, thus achieving a higher level of encryption. Triple-DES is one of the strongest
encryption algorithms available for use in VPNs.
Tspec Object RSVP message object that contains information such as the bandwidth request
of the LSP as well as the minimum and maximum packets supported.
tunnel Private, secure path through an otherwise public network.
tunnel mode An IPSec mode of operation in which the entire IP packet, including the header,
is encrypted and authenticated and a new VPN header is added, protecting the entire original
packet. This mode can be used by both VPN clients and VPN gateways, and protects communications
that come from or go to non-IPSec systems. See also transport mode.
Tunnel PIC A physical interface card that allows the router to perform the encapsulation and
decapsulation of IP datagrams. The Tunnel PIC supports IP-IP, GRE, and PIM register encapsulation
and decapsulation. When the Tunnel PIC is installed, the router can be a PIM rendezvous
point (RP) or a PIM first-hop router for a source that is directly connected to the router.
type of service (ToS) The method of handling traffic using information extracted from the
fields in the ToS byte to differentiate packet flows.
U
UMTS Terrestrial Radio Access Network (UTRAN) The WCDMA radio network in UMTS.
unicast Operation of sending network traffic from one network node to another individual
network node.
uninterruptible power supply (UPS) Device that sits between a power supply and a router
(or other piece of equipment) that prevents undesired power-source events, such as outages and
surges, from affecting or damaging the device.
unit JUNOS software syntax that represents the logical properties of an interface.
Glossary 567
Universal Mobile Telecommunications System (UMTS) Third-generation (3G), packetbased
transmission of text, digitized voice, video, and multimedia, at data rates up to 2Mbps.
Update message BGP message that advertises path attributes and routing knowledge to an
established neighbor.
Update timer Used in a distance-vector protocol to advertise routes to a neighbor on a regular
basis. The JUNOS software uses a default value of 30 seconds.
upto JUNOS software routing policy match type representing all routes that share the same
most significant bits and whose prefix length is smaller than the supplied subnet in the route
filter.
User Datagram Protocol (UDP) Layer 4 protocol that provides an unreliable, connectionless
service between two end IP hosts.
V
vapor corrosion inhibitor (VCI) Small cylinder packed with the router that prevents corrosion
of the chassis and components during shipment.
virtual circuit Represents a logical connection between two Layer 2 devices in a network.
virtual circuit identifier (VCI) A 16-bit field in the header of an ATM cell that indicates the
particular virtual circuit the cell takes through a virtual path. Also called a logical interface.
virtual link In OSPF, a link created between two routers that are part of the backbone but are
not physically contiguous.
virtual local area network (VLAN) A grouping of end hosts within a single IP subnet. These
hosts usually reside on multiple physical segments and are connected through a Layer 2 Ethernet
switched network.
virtual path A combination of multiple virtual circuits between two devices in an ATM
network.
virtual path identifier (VPI) The 8-bit field in the header of an ATM cell that indicates the virtual
path the cell takes. See also virtual circuit identifier (VCI).
virtual private network (VPN) A private data network that makes use of a public TCP/IP network,
typically the Internet, while maintaining privacy with a tunneling protocol, encryption,
and security procedures.
Virtual Router Redundancy Protocol (VRRP) On Fast Ethernet and Gigabit Ethernet interfaces,
allows you to configure virtual default routers.
568 Glossary
W
wavelength-division multiplexing (WDM) Technique for transmitting a mix of voice, data,
and video over various wavelengths (colors) of light.
Wideband Code Division Multiple Access (WCDMA) Radio interface technology used in
most third-generation systems.
weighted round-robin (WRR) Scheme used to decide the queue from which the next packet
should be transmitted.