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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
134 Switch Management and Operating Concepts
link-state updates describing every router on the
segment.
• External Link-State Updates – issued by an
Autonomous System Border Router and
describes routes to destinations outside the AS
or a default route to the outside AS.
The format of these link-state updates are described in more
detail below.
Router link-state updates are flooded to all routers in the
current area. These updates describe the destinations
reachable through all of the router’s interfaces.
Summary link-state updates are generated by Border Routers
to distribute routing information about other networks within
the AS. Normally, all Summary link-state updates are
forwarded to the backbone (area 0) and are then forwarded to
all other areas in the network. Border Routers also have the
responsibility of distributing routing information from the
Autonomous System Border Router in order for routers in the
network to get and maintain routes to other Autonomous
Systems.
Network link-state updates are generated by a router elected as
the Designated Router on a multi-access segment (with more
than one attached router). These updates describe all of the
routers on the segment and their network connections.
External link-state updates carry routing information to
networks outside the Autonomous System. The Autonomous
System Border Router is responsible for generating and
distributing these updates.