Dell BigIron RX Series, Configuration Manual

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BigIron RX Series Configuration Guide 869
53-1002253-01
Configuring IS-IS (IPv4)
28
NOTE
Since the Brocade implementation of IS-IS does not route OSI traffic but instead routes IP traffic, IP
hosts are shown instead of ESs.
The other basic IS-IS concepts illustrated in this figure are explained in the following sections.
Domain and areas
IS-IS is an IGP, and thus applies only to routes within a single routing domain. However, you can
configure multiple areas within a domain. A device can be a member of one area for each Network
Entity Title (NET) you configure on the device. The NET contains the area ID for the area the NET is
in.
In Figure 117 , Routers A, B, and C are in area 1. Routers D and E are in area 2. All the routers are in
the same domain.
Level-1 routing and Level-2 routing
You can configure an IS-IS router such as a device to perform one or both of the following levels of
IS-IS routing
1
:
•
Level-1 – A Level-1 router routes traffic only within the area the router is in. To forward traffic to
another area, the Level-1 router sends the traffic to its nearest Level-2 router.
•
Level-2 – A Level-2 router routes traffic between areas within a domain.
In Figure 117 on page 868, Routers A and B are Level-1s only. Routers C and D are Level-1 and
Level-2 ISs. Router E is a Level-1 IS only.
Neighbors and adjacencies
A device configured for IS-IS forms an adjacency with each of the IS-IS devices to which it is directly
connected. An adjacency is a two-way direct link (a link without router hops) over which the two
devices can exchange IS-IS routes and other protocol-related information. The link is sometimes
called a “circuit”. The devices with which the device forms adjacencies are its
neighbors , which are
other ISs.
A BigIron RX IS-IS interfaces are configured by default for broadcast circuits.
In Figure 117 on page 868, Router A has an IS-IS adjacency with Router B. Likewise, Router B has
an IS-IS adjacency with Router A and Router C.
Designated IS
A Designated IS is an IS-IS router that is responsible for gathering and distributing link state
information to other Level-1 or Level-2 ISs within the same broadcast network (LAN). The Level-1
and Level-2 Designated ISs within a broadcast network are independent, although the same device
can be a Level-1 Designated IS and a Level-2 Designated IS at the same time.
1. The ISO/IEC specifications use the spelling “routeing”, but this document uses the spelling
“routing” to remain consistent with other Brocade documentation.