Advanced OSPF Design Concepts | OSPF Network Design Solutions

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Example: The following example sets the router priority value to 4:

    interface ethernet 0    ip ospf priority 4

Related Commands: ip ospf network, neighbor (OSPF)

ip ospf retransmit-interval

To specify the time between LSA retransmissions for adjacencies belonging to the interface, use the ip ospf retransmit-interval interface configuration command. To return to the default value, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf retransmit-interval seconds    no ip ospf retransmit-interval

Syntax Description:

seconds. Time in seconds between retransmissions. It must be greater than the expected round-trip delay between any two routers on the attached network. The range is 1 to 65535 seconds. The default is 5 seconds.

Default: 5 seconds.

Command Mode: Interface configuration.

Usage Guidelines: When a router sends a LSA to its neighbor, it keeps the LSA until it receives back the acknowledgment. If it receives no acknowledgment in seconds, it will retransmit the LSA.

The setting of this parameter should be conservative, or needless retransmission will result. The value should be larger for serial lines and virtual links.

Example: The following example sets the retransmit-interval value to eight seconds:

    interface ethernet 2    ip ospf retransmit-interval 8

ip ospf transmit-delay

To set the estimated time it takes to transmit a link-state update packet on the interface, use the ip ospf transmit-delay interface configuration command. To return to the default value, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf transmit-delay seconds    no ip ospf transmit-delay

Syntax Description:

seconds. Time in seconds that it takes to transmit a link-state update. It can be an integer in the range is 1 to 65,535 seconds. The default is 1 second.

Default: 1 second.

Command Mode: Interface configuration.

Usage Guidelines: LSAs in the update packet must have their age incremented by the amount specified in the seconds argument before transmission. The value assigned should take into account the transmission and propagation delays for the interface.

If the delay is not added before transmission over a link, the time in which the LSA propagates over the link is not considered. This setting has more significance on very low speed links.

Example: The following example sets the retransmit-delay value to three seconds:

    interface ethernet 0    ip ospf transmit-delay 3

ip policy route-map

To identify a route map to use for policy routing on an interface, use the ip policy route-map interface configuration command. To disable policy routing on the interface, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip policy route-map map-tag    no ip policy route-map map-tag

Syntax Description:

map-tag. Name of the route map to use for policy routing. Must match a map-tag specified by a route-map command.

Default: No policy routing occurs on the interface.

Command Mode: Interface configuration.

Usage Guidelines: You might enable policy routing if you want your packets to take a route other than the obvious shortest path. The ip policy route-map command identifies a route map to use for policy routing. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which policy routing is allowed for the interface. The set commands specify the set actions—the particular policy routing actions to perform if the criteria enforced by the match commands are met. The no ip policy route-map command deletes the pointer to the route map.

Example: In the following example, packets with the destination IP address of 174.95.16.18 are sent to a router at IP address 174.21.3.20:

    interface serial 0    ip policy route-map wethersfield    !    route-map wethersfield    match ip address 174.95.16.18    set ip next-hop 174.21.3.20

Related Commands: match ip address, match length, route-map, set default interface, set interface, set ip default next-hop, set ip next-hop

neighbor (OSPF)

To configure OSPF routers and access servers interconnecting to nonbroadcast networks, use this form of the neighbor router configuration command. To remove a configuration, use the no form of this command. The syntax for this command (and the no form) is as follows:

    neighbor ip-address [priority number] [poll-interval seconds]    no neighbor ip-address [priority number] [poll-interval seconds]

TIPS:
The command neighbor <address> cost <value> can be used to specify per neighbor cost on a point-to-multipoint network. This value takes precedence over the interface cost.

Syntax Description:

ip-address. Interface IP address of the neighbor.

priority number (optional). 8-bit number indicating the router priority value of the nonbroadcast neighbor associated with the IP address specified. The default is 0.

poll-interval seconds (optional). Unsigned integer value reflecting the poll interval. RFC 1247 recommends that this value be much larger than the hello interval. The default is two minutes (120 seconds).

Default: No configuration is specified.

Command Mode: Router configuration.

Usage Guidelines: X.25 and Frame Relay provide an optional broadcast capability that can be configured in the map to allow OSPF to run as a broadcast network. At the OSPF level you can configure the router as a broadcast network. See the x25 map and frame-relay map commands in “X.25 Commands” and “Frame Relay Commands” chapters, respectively, in the Wide-Area Networking Command Reference for more detail.

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