Neighbors And Adjacencies; Designated Is - Dell PowerConnect B-RX Configuration Manual

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In this chapter
In Figure 117
Level-2 ISs. Router E is a Level-1 IS only.

Neighbors and adjacencies

A BigIron RX 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.
BigIron RX IS-IS interfaces are configured by default for broadcast circuits.
In Figure 117
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
BigIron RX can be a Level-1 Designated IS and a Level-2 Designated IS at the same time.
The Designated IS is elected based on the priority of each IS in the broadcast network. When an IS
becomes operational, it sends a Level-1 or Level-2 Hello PDU to advertise itself to other ISs. If the
IS is configured to be both a Level-1 and a Level-2 IS, the IS sends a separate advertisement for
each level.
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If the Designated IS becomes unavailable (for example, is rebooted), the IS with the next highest
priority becomes the new IS. If two or more ISs have the highest priority, the IS with the highest MAC
address becomes the Designated IS.
The priority is an interface parameter. Each interface that is enabled for IS-IS can have a different
priority.
882
on page 881, Routers A and B are Level-1s only. Routers C and D are Level-1 and
on page 881, Router A has an IS-IS adjacency with Router B. Likewise, Router B has
The Level-1 IS that has the highest priority becomes the Level-1 Designated IS for the
broadcast network.
The Level-2 IS that has the highest priority becomes the Level-2 Designated IS for the
broadcast network.
BigIron RX Series Configuration Guide
53-1001810-01