Brocade Communications Systems ICX 7250 series, Руководство по настройке

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For more information about redistribution, refer to the redistribute command in the FastIron Command Reference .
Designated routers
In an OSPF broadcast network, OSPF elects one router to serve as the designated router (DR) and another router on the segment to act
as the backup designated router (BDR). This minimizes the amount of repetitive information that is forwarded on the network. OSPF
forwards all messages to the designated router.
On broadcast networks such as LAN links, all routers on the LAN other than the DR and BDR form full adjacencies with the DR and
BDR and pass LSAs only to them. The DR forwards updates received from one neighbor on the LAN to all other neighbors on that same
LAN. One of the main functions of a DR is to ensure that all the routers on the same LAN have identical LSDBs. Therefore, on broadcast
networks, an LSDB is synchronized between a DROther (a router that is not a DR or a BDR) and its DR and BDR.
NOTE
In an OSPF point-to-point network, where a direct Layer 3 connection exists between a single pair of OSPF routers, there is no
need for designated or backup designated routers.
Without the need for Designated and Backup Designated routers, a point-to-point network establishes adjacency and converges faster.
The neighboring routers become adjacent whenever they can communicate directly. In contrast, in broadcast and non-broadcast multi-
access (NBMA) networks, the Designated Router and Backup Designated Router become adjacent to all other routers attached to the
network.
In a network with no designated router and no backup designated router, the neighboring router with the highest priority is elected as the
DR, and the router with the next highest priority is elected as the BDR, as shown in the figure below. Priority is a configurable option at
the interface level; refer to the
ip ospf priority command in the FastIron Command Reference.
FIGURE 18 Designated and backup router election
If the DR goes off line, the BDR automatically becomes the DR. The router with the next highest priority becomes the new BDR.
If two neighbors share the same priority, the router with the highest router ID is designated as the DR. The router with the next highest
router ID is designated as the BDR. The DR and BDRs are recalculated after the OSPF protocol is disabled and re-enabled by means of
the
[no] router ospf command.
NOTE
By default, the Brocade device’s router ID is the IP address configured on the lowest numbered loopback interface. If the device
does not have a loopback interface, the default router ID is the lowest numbered IP address configured on the device.
When multiple routers on the same network are declaring themselves DRs, then both the priority and router ID are used to select the
designated router and backup designated routers.
OSPFv2 components and roles
Brocade FastIron Layer 3 Routing Configuration Guide
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