Is-Is Terms; Table 13: Is-Is Terms - Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual

JUNOSe 11.0.x IP, IPv6, and IGP Configuration Guide
hierarchical routing design is used. With this model, routing is referred to as level 1,
level 2, or both level 1 and level 2.

IS-IS Terms

OSI internetworking has its own terminology. A number of terms used in IS-IS routing
discussions are defined in Table 13 on page 326.

Table 13: IS-IS Terms

326
Overview
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