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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 133
receive particular link-state updates are located. This helps
ensure that routing updates are not flooded throughout the
entire network and to reduce the amount of bandwidth
consumed by updating the various router’s routing tables.
Areas establish boundaries beyond which link-state updates do
not need to be flooded. So the exchange of link-state updates
and the calculation of the shortest path tree are limited to the
area that the router is connected to.
Routers that have connections to more than one area are called
Border Routers (BR). The Border Routers have the
responsibility of distributing necessary routing information and
changes between areas.
Areas are specific to the router interface. A router that has all
of its interfaces in the same area is called an Internal Router.
A router that has interfaces in multiple areas is called a Border
Router. Routers that act as gateways to other networks
(possibly using other routing protocols) are called Autonomous
System Border Routers (ASBRs).
Link-State Packets
There are different types of link-state packets, four are
illustrated below:
• Router Link-State Updates − these describe a
router’s links to destinations within an area.
• Summary Link-State Updates – issued by Border
Routers and describe links to networks outside
the area but within the Autonomous System (AS).
• Network Link-State Updates – issued by multi-
access areas that have more than one attached
router. One router is elected as the Designated
Router (DR) and this router issues the network