Is-Is Domain - H3C S7500 Series Operation Manual

Operation Manual – Routing Protocol
H3C S7500 Series Ethernet Switches
of the IS. Each IS collects all the LSPs in the local area to generate its own
LSDB.
Network protocol data unit (NPDU). An NPDU is a network layer protocol packet
in OSI, which is equivalent to an IP packet in TCP/IP.
Designated IS (DIS). On a broadcast network, the designated router is also
known as the designated IS.
Network service access point (NSAP). The NSAP is the OSI network layer
address. It identifies an abstract network service access point and describes the
network address in the OSI reference model.
II. IS-IS network types
IS-IS supports two network types:
Broadcast networks, such as Ethernet and Token-Ring
Point-to-point networks, such as PPP and HDLC
For non-broadcast multi-access (NBMA) network, such as ATM, you need to
configure point-to-point or broadcast network on its sub-interfaces. IS-IS does not run
on point to multipoint (P2MP) links.

5.1.2 IS-IS Domain

I. Two-level hierarchy
The IS-IS uses two-level hierarchy in the routing domain to support large scale routing
networks. A large routing domain is divided into multiple Areas. The Level-1 router is
in charge of forwarding routes within an area, and the Level-2 router is in charge of
forwarding routes between areas.
II. Level-1 and Level-2
1) Level-1 router
The Level-1 router only forms the neighbor relationship with Level-1 and Level-1-2
routers in the same area. The LSDB maintained by the Level-1 router contains the
local area routing information. It directs the packets out of the area to the nearest
Level-2 router.
2) Level-2 router
The Level-2 router forms the neighbor relationship with the Level-2 and Level-1-2
routers in the same or in different areas. It maintains a Level-2 LSDB which contains
routing information for routing between areas. All Level-2 routers must be contiguous
to form the backbone in a routing domain. Only Level-2 routers can directly
communicate with routers outside the routing domain. Level-2 routers in a routing
domain must be contiguous to ensure a contiguous backbone network.
3) Level-1-2 router
5-2
Chapter 5 IS-IS Configuration