Default Distance Weights: Table 6-1 provides you with the accepted default values for weights.
Command Mode: Router configuration.
Usage Guidelines: Numerically, an administrative distance is an integer between 0 and 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.
When the optional access list number is used with this command, it is applied when a network is being inserted into the routing table. This behavior allows filtering of networks according to the IP address of the router supplying the routing information. This could be used, as an example, to filter out possibly incorrect routing information from routers not under your administrative control.
The order in which you enter distance commands can affect the assigned administrative distances in unexpected ways (see Example for further clarification). Weight values are also subjective; there is no quantitative method for choosing weight values.
For BGP, the distance command sets the administrative distance of the External BGP route. The show ip protocols EXEC command displays the default administrative distance for a specified routing process.
Example: In the following example, the router igrp global configuration command sets up IGRP routing in autonomous system number 109. The network router configuration commands specify IGRP routing on networks 18.104.22.168 and 22.214.171.124. The first distance router configuration command sets the default administrative distance to 255, which instructs the Cisco IOS software to ignore all routing updates from routers for which an explicit distance has not been set. The second distance command sets the administrative distance for all routers on the Class C network 126.96.36.199 to 90. The third distance command sets the administrative distance for the router with the address 188.8.131.52 to 120.
router igrp 109 network 184.108.40.206 network 220.127.116.11 distance 255 distance 90 18.104.22.168 0.0.0.255 distance 120 22.214.171.124 0.0.0.0
To suppress networks from being advertised in updates, use the distribute-list out router configuration command. To cancel this function, use the no form of this command. The syntax for this command (and the no form) is as follows:
distribute-list access-list-number out [interface-name | routing-process | autonomous-system-number] no distribute-list access-list-number out [interface-name | routing-process | autonomous-system-number]
Command Mode: Router configuration.
Usage Guidelines: When redistributing networks, a routing process name can be specified as an optional trailing argument to the distribute-list command. This causes the access list to be applied to only those routes derived from the specified routing process. After the process-specific access list is applied, any access list specified by a distribute-list command without a process name argument will be applied. Addresses not specified in the distribute-list command will not be advertised in outgoing routing updates.
Example: The following example would cause only one network to be advertised by a RIP router and will not work for OSPF.
process: network 126.96.36.199. access-list 1 permit 188.8.131.52 access-list 1 deny 0.0.0.0 255.255.255.255 router rip network 184.108.40.206 distribute-list 1 out
ip ospf authentication-key
To assign a password to be used by neighboring routers that are using OSPFs simple password authentication, use the ip ospf authentication-key interface configuration command. To remove a previously assigned OSPF password, use the no form of this command. The syntax for this command (and the no form) is as follows:
ip ospf authentication-key password no ip ospf authentication-key
Default: No password is specified.