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
