Administrative Distance

Administrative Distance: -

·         An administrative distance is the metric used by routers to choose the best path when there are two or more routes to the same destination from two different routing protocols.

·         Administrative distance is 8 bits (0-255) value.

·         An administrative distance guides the selection of one routing protocol over another.

·         You can modify the administrative distance of a protocol through the distance command in the routing process sub-configuration mode.

·         The smaller administrative distance value is more reliable.

·         Administrative distance has only local significance.

·         Administrative distance not advertised in routing updates.

·         If the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table.

·         Administrative distance 0 is highly trusted.

 

Different Protocol default AD values: -

            

Change Administrative distance: -

·         STATIC AD:

                              R(Config)#ip route (Network)    (Subnet Mask) (Next-hop) (AD)

                              R(Config)#ip route 192.168.1.0      255.0.0.0        172.16.1.1     2

·         RIP AD: -

     R(Config)#router rip

     R(Config-router) # distance (AD value)

·         EIGRP AD: -

     R(Config)#router eigrp 100

     R(Config-router) # distance (AD value)

·         OSPF AD: -

     R(Config)#router ospf 100

     R(Config-router) # distance (AD value)

Verify Administrative distance: -

             R# show ip route    

                    C    20.0.0.0/8 is directly connected, FastEthernet0/0    

                     S    40.0.0.0/8 [1/0] via 20.0.0.2

                     C    10.0.0.0/8 is directly connected, FastEthernet0/1

                     S    30.0.0.0/8 [1/0] via 20.0.0.2