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Cisco: Default static routes with different administrative distances

Posted on 2014-11-23
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Last Modified: 2015-01-02
I have a Cisco router that has two default routes configured:
ip route 0.0.0.0 0.0.0.0 10.1.236.6 250
ip route 0.0.0.0 0.0.0.0 10.1.35.5 254

The question I have is why is the default route with a AD of 250 showing up in the routing table when it seems that the other default with the AD of 254 should show up in the routing table to be used as the default route?

Here is a copy of the show ip route display:
R3# sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 10.1.236.6 to network 0.0.0.0

S*    0.0.0.0/0 [250/0] via 10.1.236.6
      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
S        10.1.1.1/32 [1/0] via 11.1.1.1
C        10.1.3.3/32 is directly connected, Loopback0
C        10.1.35.0/24 is directly connected, Serial4/0
L        10.1.35.1/32 is directly connected, Serial4/0
C        10.1.123.0/24 is directly connected, Ethernet0/0
L        10.1.123.3/32 is directly connected, Ethernet0/0
C        10.1.236.0/24 is directly connected, Ethernet0/1
L        10.1.236.3/32 is directly connected, Ethernet0/1
      11.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        11.1.1.0/24 is directly connected, Tunnel23
L        11.1.1.3/32 is directly connected, Tunnel23
      32.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        32.0.0.0/24 is directly connected, Tunnel0
L        32.0.0.3/32 is directly connected, Tunnel0
R3#

Here is a copy of the run config | s route:
R3#sh run | b route
ip route 0.0.0.0 0.0.0.0 10.1.236.6 250
ip route 0.0.0.0 0.0.0.0 10.1.35.5 254
R3#
0
Comment
Question by:dsterling
5 Comments
 
LVL 28

Assisted Solution

by:Predrag Jovic
Predrag Jovic earned 125 total points
ID: 40460829
Other route should not appear.
Lower AD is always preferred if specificity of routes is the same.
Both routes are equally specific so route lower AD won.
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LVL 28

Assisted Solution

by:Jan Springer
Jan Springer earned 125 total points
ID: 40460870
the higher the number the greater the distance and thus less preferred.
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LVL 10

Assisted Solution

by:Rafael
Rafael earned 125 total points
ID: 40461132
I concur as well lower AD is always better.  Here is a great article from Cisco that explains it as well as contains a chart on it with AD Default Distance Value Tables.

-HTH

Rafael
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Accepted Solution

by:
Otto_N earned 125 total points
ID: 40461655
As the experts above already stated, the lower AD is preferred.

But you might then ask: "Why two static routes, if only one will ever make it into the routing table?"  The answer - In case the first-choice gateway dies.  The only time you'll see the default route via 10.1.35.5 in the routing table, is when you loose visibility to 10.1.236.0/24 (i.e. if Eth0/1 goes down).  It seems that the router is configured to route via Eth0/1, but if Eth0/1 fails, traffic gets routed via Ser4/0.

Note that the second static route will not activate if only 10.1.236.6 gets removed from the Ethernet segment - this will still leave 10.1.236.0/24 in the routing table, and the first static route active.  The second static route will only be inserted in the routing table if the 10.1.236.0/24 subnet disappears from the routing table completely, such as when the interface gets shut, disconnected, or reconfigured with a different IP subnet.
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Author Closing Comment

by:dsterling
ID: 40527893
Good comment's, I'll keep looking.
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