Router Types - Avaya 8800 Configuration Manual

All routers connected by a point-to-point network or a virtual link always form an adjacency. All
routers on a broadcast or NBMA network form an adjacency with the DR and the BDR.
In an NBMA network, before a DR is elected, the router sends Hello packets only to those
neighbors eligible to become a DR. The NBMA DR forms adjacencies only with its configured
neighbors and drops all packets from other sources. The neighbor configuration also notifies
the router of the expected Hello behavior for each neighbor.
If a router receives a Hello packet from a neighbor with priority different from that which is
already configured for the neighbor, the router can automatically change the configured priority
to match the dynamically learned priority.

Router types

To limit the amount of routing protocol traffic, the Hello Protocol elects a designated router (DR)
and a backup designated router (BDR) on each multiaccess network. Instead of neighboring
routers forming adjacencies and swapping link-state information (which on a large network can
mean significant routing protocol traffic), all routers on the network form adjacencies with the
DR and the BDR only, and send link-state information to them. The DR redistributes this
information to every other adjacent router.
When operating in backup mode, the BDR receives link-state information from all routers on
the network and listens for acknowledgements. If the DR fails, the BDR can transition quickly
to the role of DR because its routing tables are up to date.
Routers in an OSPF network can have various roles depending on how you configure them.
The following table describes the router types you can configure in an OSPF network.
Table 5: Router types in an OSPF network
Router type
AS boundary router
(ASBR)
Area border router (ABR) A router attached to two or more areas inside an OSPF network
Internal router (IR)
Configuration — OSPF and RIP
A router attached at the edge of an OSPF network is called an
ASBR. An ASBR generally has one or more interfaces that run
an inter-domain routing protocol such as BGP. In addition, any
router that distributes static routes or RIP routes into OSPF is
considered an ASBR. The ASBR forwards external routes into
the OSPF domain. In this way, routers inside the OSPF network
learn about destinations outside their domain.
is considered an ABR. ABRs play an important role in OSPF
networks by condensing the amount of disseminated OSPF
information.
A router that has interfaces only within a single area inside an
OSPF network is considered an IR. Unlike ABRs, IRs have
topological information only about the area in which they are
contained.
Open Shortest Path First
Description
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