Ospf Routers; Router Types - Avaya ERS 8800 series Configuration Manual

IPv6 routing fundamentals
Important:
If a router receives a hello packet from a neighbor with a priority different from the configured
priority, the router automatically changes the configured priority to match the dynamically
learned priority.

OSPF routers

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 with each other (which, on a
large network, can mean a large volume of routing protocol traffic), all routers on the network
form adjacencies only with the DR and the BDR and send link-state information to the DR and
BDR. The DR redistributes this information to every other adjacent router.
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 transitions quickly to the role of DR
because routing tables are up to date.

Router types

Routers in an OSPF network can perform different roles depending on router configuration.
Table 6: Router types in an OSPF network
configure in an OSPF network.
Table 6: 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)
Designated router (DR)
40 Configuration — IPv6 Routing
on page 40 describes the router types you can
A router attached at the edge of an OSPF network is called an
AS boundary router (ASBR). An ASBR uses one or more
interfaces that run an interdomain routing protocol such as the
Border Gateway Protocol (BGP). In addition, any router
distributing static routes or Routing Information Protocol (RIP)
routes into OSPF is 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 an area border router (ABR). ABRs play an important role in
OSPF networks by condensing the amount of OSPF
information that is disseminated.
A router that uses interfaces only within a single area inside an
OSPF network is an internal router (IR). Unlike ABRs, IRs use
topological information only about the local area.
In a broadcast or NBMA network, a single router is the
designated router (DR) for that network. A DR ensures that all
Description
November 2010