3Com Switch 7750 Configuration Guide

OSPF Network Adjustment and Optimization 317
Configuration
Prerequisites
Before adjusting and optimizing an OSPF network, perform the following tasks:
■ Configuring the network layer addresses of interfaces so that the adjacent
nodes are reachable to each other at the network layer
■ Configuring basic OSPF functions
Configuring OSPF Timers The Hello intervals for OSPF neighbors must be consistent. The value of Hello
interval is in inverse proportion to route convergence speed and network load.
The dead time on an interface must be at least four times of the Hello interval on
the same interface.
After a router sends an LSA to a neighbor, it waits for an acknowledgement
packet from the neighbor. If the router receives no acknowledgement packet from
the neighbor within the retransmission interval, it retransmits the LSA to the
neighbor.
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■ Default Hello and Dead timer values will be restored once the network type is
changed.
■ Do not set an LSA retransmission interval that is too short. Otherwise,
unnecessary retransmission will occur. LSA retransmission interval must be
greater than the round trip time of a packet between two routers.
Table 242 Configure OSPF timers
Operation Command Description
Enter system view system-view -
Enter interface view interface interface-type
interface-number
-
Set the hello interval on the interface ospf timer hello seconds Optional
By default, p2p and
broadcast interfaces send
Hello packets every 10
seconds; while p2mp and
NBMA interfaces send
Hello packets every 30
seconds.
Set the poll interval on the NBMA
interface
ospf timer poll seconds Optional
By default, poll packets are
sent every 120 seconds.
Set the dead time of the neighboring
router on the interface
ospf timer dead seconds Optional
By default, the dead time
for the OSPF neighboring
router on a p2p or
broadcast interface is 40
seconds and that for the
OSPF neighboring router
on a p2mp or NBMA
interface is 120 seconds.
Set the interval at which the router
retransmits an LSA to the
neighboring router on the interface
ospf timer retransmit
interval
Optional
By default, this interval is
five seconds.