Cisco Systems CL-28826-01 Understanding OSPF Timer Settings

64-28

User Guide for Cisco Security Manager 4.4

OL-28826-01

Chapter 64 Configuring Routing Policies

OSPF Routing on Cisco IOS Routers

Related Topics

•Understanding Interface Cost, page 64-26

•Understanding Interface Priority, page64-26

•Disabling MTU Mismatch Detection, page 64-27

•Understanding OSPF Timer Settings, page 64-28

•Understanding the OSPF Network Type, page 64-29

•Understanding OSPF Interface Authentication, page 64-29

•Defining OSPF Interface Settings, page 64-25

Understanding OSPF Timer Settings

OSPF uses a series of timers during operation:

•Hello Interval—Determines how often an interface sends hello packets, which are used to acquire

neighbors and act as indicators that the router is still functioning. The smaller the interval, the faster

topological changes on the network are detected. However, a smaller interval also results in more

traffic being sent over the interface. The hello interval must be the same on all routers and access

servers on a specific network.

•Transmit Delay—Determines the delay before an LSA is flooded over the link. The transmit delay

setting should take into account the transmission and propagation delays for the interface. These

factors are particularly important when configuring low-speed and on-demand links.

•Retransmit Interval—Determines how long to wait before retransmitting an unacknowledged

database description (DBD) packet to its neighbors. The retransmit interval setting should be low

enough to prevent excessive retransmissions.

Note You should increase the retransmit interval for serial lines and virtual links.

•Dead Interval—Determines how long an interface should wait before declaring its neighbor to be

down. This declaration is caused by an absence of hello packets from the neighbor during this

interval. The dead interval setting must be the same for all routers and access servers on a specific

network. By default, this interval is four times the hello interval.