Neighbors and adjacencies, Designated is – Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Routing Configuration Guide
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Relationship to IP route table
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Level-2 – A Level-2 router routes traffic between areas within a domain.
In
on page 250, 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 Brocade 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 Brocade device forms adjacencies are its
neighbors, which are other ISs.
on page 250, 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
Brocade device 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:
•
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.
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.