Command
Distance
Use
Allows you to filter routes from the routing table. For CCNA purposes, this is usually done through access lists.
Syntax
Router(config-router)#distance <AD> <source IP> <wildcard mask> <access-list>
Options
<Administrative Distance> | Sets the administrative distance for the selected routes |
<source IP> | Source IP the route is received from |
<wildcard mask> | Specifies a wildcard mask, allows you to specify multiple source IP addresses |
<access-list> | Specifies an access-list that selects what routes will have their AD changed |
Example
In this example, we will apply a change to the administrative distance for OSPF to 123 for any route that starts with 1.0.0.0. First, we’ll look at the routing table.
R2(config)#do show ip route ospf 1.0.0.0/32 is subnetted, 3 subnets O 1.1.1.1 [110/66] via 10.2.2.3, 00:00:22, FastEthernet1/0 O 1.3.3.3 [110/66] via 10.2.2.3, 00:00:22, FastEthernet1/0 O 1.2.2.2 [110/66] via 10.2.2.3, 00:00:22, FastEthernet1/0 192.168.13.0/30 is subnetted, 1 subnets O 192.168.13.0 [110/65] via 10.2.2.3, 00:00:22, FastEthernet1/0 33.0.0.0/32 is subnetted, 1 subnets O 33.33.33.33 [110/2] via 10.2.2.3, 00:00:22, FastEthernet1/0 3.0.0.0/32 is subnetted, 1 subnets O 3.3.3.3 [110/2] via 10.2.2.3, 00:00:22, FastEthernet1/0 111.0.0.0/32 is subnetted, 1 subnets O 111.111.111.111 [110/66] via 10.2.2.3, 00:00:22, FastEthernet1/0 10.0.0.0/24 is subnetted, 3 subnets O 10.4.4.0 [110/65] via 10.2.2.3, 00:00:22, FastEthernet1/0 11.0.0.0/32 is subnetted, 1 subnets O 11.11.11.11 [110/66] via 10.2.2.3, 00:00:22, FastEthernet1/0 133.133.0.0/32 is subnetted, 1 subnets O 133.133.133.133 [110/2] via 10.2.2.3, 00:00:22, FastEthernet1/0
Now, we will configure the distance command on R2’s OSPF process.
R2(config)#access-list 25 permit 1.0.0.0 0.255.255.255 R2(config)#router ospf 1 R2(config-router)#distance 123 10.1.1.1 255.255.255.255 25
Finally, we see routes starting with 1.0.0.0 now have an administrative distance of 123.
R2(config-router)#do show ip route ospf 1.0.0.0/32 is subnetted, 3 subnets O 1.1.1.1 [123/2] via 10.1.1.1, 00:00:03, FastEthernet0/0 O 1.3.3.3 [123/2] via 10.1.1.1, 00:00:03, FastEthernet0/0 O 1.2.2.2 [123/2] via 10.1.1.1, 00:00:03, FastEthernet0/0 192.168.13.0/30 is subnetted, 1 subnets O 192.168.13.0 [110/65] via 10.2.2.3, 00:00:03, FastEthernet1/0 [110/65] via 10.1.1.1, 00:00:03, FastEthernet0/0