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Does any one knows a way to configure a cisco router with multiple gateways - multiple gateways of last resort?

I've tried adding a gateway of last resort twice (with different metric) but only one is shown:

Router(config)# ip route 10
Router(config)# ip route 100

And the show ip route output was:

Router# show ip route
Gateway of last resort is to network is subnetted, 1 subnets
C is directly connected, FastEthernet0/0 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1 is subnetted, 1 subnets
C is directly connected, Serial0/2/0
S* [10/0] via

The point is that i cannot see the other route with higher distance metric?

Anyone has a sugestion?

I mean will this config work if the link on fails? Will the router choose the other network, if the link fails?

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Please explain the downvote? – SpacemanSpiff Nov 25 '11 at 14:36

3 Answers 3

up vote 6 down vote accepted

IIRC, if you put different metrics only the best route will be injected in the main routing table.

So you have three choices:

First choice, as @dkaragasidis said, don't put the metrics (to get per session load-balancig) but then the traffic will flow nearly 50% on both links

Second choice, use some sort of dynamic routing protocol (i suggest BGP) if possbile.

Third choice, use ip sla commands to costantly check for ip availability.

Keep in mind that if one FastEthernet interface (or the remote port with which is connected) fails (i.e. the status of the interface goes to down) then the router automatically injects the other default route, but NOT if the router somehow doesn't work (in that case the ip sla commands will take care of this).

If BGP is not an option and you really don't wanto to balance the gateways, ip sla is your best solution. Take a look at this answer to a similar question for a link to some examples.

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Thank you MrShunz your answer was usefull.. I guess I will try the third one :) – Spirit Nov 28 '11 at 9:10

Consider checking out Cisco's Configuring a Gateway of Last Resort Using IP Commands.

If you use multiple ip route commands to configure a default route, traffic is load-balanced over the multiple routes.

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With having multiple default routes you can load-balance the traffic ( session lb ).
If you want to keep one of the paths as backup , then you need to play with metric. Give a higher metric to the path you wanna use as backup and smaller metric to the main one. This will solve your issue.
By the way because main default route will be there although the next hop is lost , you need to configure a tracker and ip sla to check the availability. If Ip Sla is down and the route will be deleted and the backup route will be inserted to your routing table.

Another solution is to define the outgoing interface instead of next-hop. Here you dont need ip sla

 ip route fa0/0 10  -->  main route ip route fa0/1 100                  -->  backup route
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