
IP Concepts, Terminology, and Features
308627-14.00 Rev 00
1-15
Routers connected by a point-to-point network or a virtual link always form an
adjacency. Also, every router on a multiaccess network forms an adjacency
relationship with the designated router and the backup designated router.
Designated Routers
To further reduce the amount of routing traffic, the Hello protocol elects a
designated router and a backup designated router on each multiaccess network.
Instead of neighboring routers forming adjacencies and swapping link-state
information with each other (which on a large network can mean a lot of routing
protocol traffic), all routers on the network form adjacencies with the designated
router and the backup designated router only and send link-state information to
them. The designated router then distributes the information from each router to
every other router.
The Hello protocol always elects a backup designated router along with the
designated router. This router takes over all of the designated router’s functions
should the designated router fail.
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