l Backing up only the OSPF configuration: After the switchover between the AMB and the
SMB, OSPF performs graceful restart (GR), obtains the adjacency relationship from
neighbors, and synchronizes the LSDBs.
Smart-discover
Generally, switches periodically send Hello packets through interfaces that run OSPF,
switches set up and maintain the neighbor relationship, and elect the DR and the Backup
Designated Router (BDR) on the multi-access network (broadcast or NBMA) by exchanging
Hello packets. When establishing the neighbor relationship or electing the DR and the BDR on
the multi-access network, interfaces can send Hello packets only when the Hello timer expires.
This affects the speed for establishing the neighbor relationship and electing the DR and the
BDR.
NOTE
l The interval for sending Hello packets on an interface depends on the interval for sending Hello packets
set on the interface.
l The default value of the interval for sending Hello packets varies with the network type.
The Smart-discover function can solve the preceding problem.
l In broadcast and NBMA networks, the neighbor relationship can be established rapidly and
a DR and a BDR on the networks can be elected rapidly.
When the neighbor status becomes 2-way for the first time, or it returns to Init from the 2-
way or higher state as shown in Figure 4-3, the interface enabled with the Smart-discover
function sends Hello packets to the neighbor without waiting for the timeout of the Hello
timer when the interface finds that the status of the neighbor changes.
When the interface status of the DR and the BDR in the multi-access network changes, the
interface enabled with the Smart-discover function sends Hello packets to the network
segment and takes part in the DR or BDR election.
Figure 4-3 Changes of the neighbor state machine
Down
FullLoadingExchange Exstart 2-wayInit
Attempt
(NBMA)
l On P2P and P2MP networks, the adjacency relationship can be established rapidly. The
principle is the same as that in broadcast and NBMA networks.
OSPF GR
When a switch restarts or performs the active/standby switchover, it directly ages all routing
entries in the Forward Information Base (FIB) table. This results in route interruption. In
addition, neighboring switchs remove this switch from the neighbor list, and notify other
switchs. This causes the re-calculation of SPF. If this switch recovers within a few seconds, the
neighbor relationship becomes unstable. This results in route flapping.
S6700 Series Ethernet Switches
Configuration Guide - IP Routing 4 OSPF Configuration
Issue 01 (2012-03-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
88
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