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JunosE 11.3.x IP, IPv6, and IGP Configuration Guide
IS-IS Terms
318
enables you to configure IS-IS as an IP routing protocol only. In IS-IS, networks are
partitioned into routing domains, which are further divided into areas. A two-level
hierarchical routing design is used. With this model, routing is referred to as level 1, level
2, or both level 1 and level 2.
OSI internetworking has its own terminology. A number of terms used in IS-IS routing
discussions are defined in Table 13 on page 318.
Table 13: IS-IS Terms
Term
area
complete sequence number
PDU (CSNP)
Connectionless Network
Protocol (CLNP)
Connectionless Network
Service Protocol (CLNS)
end system (ES)
intermediate system (IS)
level 1 routing
level 2 routing
link-state PDU (LSP)
Meaning
A group of contiguous networks and their attached hosts. Area
boundaries are normally assigned by a network administrator.
PDU sent by designated router to ensure database synchronization
An OSI network layer protocol used by CLNS to handle data at the
transport layer; the OSI equivalent of IP
An OSI network layer service that enables data transmission without
establishing a circuit and that routes messages independently of
any other messages.
Any nonrouting network node or host
A router
Routing within an area
Level 1 routers (or intermediate systems) track all the individual
links, routers, and end systems within a level 1 area.
Level 1 routers do not know the identity of routers or destinations
outside their area.
A level 1 router forwards all traffic for destinations outside its
area to the nearest level 2 router within its area.
Routing between areas
Level 2 routers know the level 2 topology and know which
addresses are reachable via each level 2 router.
Level 2 routers track the location of each level 1 area.
Level 2 routers are not concerned with the topology within any
level 1 area (for example, the details internal to each level 1 area).
Level 2 routers can identify when a level 2 router is also a level 1
router within the same area.
Only a level 2 router can exchange packets with external routers
located outside its routing domain.
PDU broadcast by link-state protocols that contains information
about neighbors and path costs; used to maintain routing tables;
also known as link-state advertisement
Copyright © 2010, Juniper Networks, Inc.
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