Secondary Static Routes

Unanswered Question
Jan 6th, 2010

I want to use two static routes for my 3750's.  I have multiple VLANs on the 3750 and I just have a single /30 point to point connection to a 6513.


I am adding a second /30 connection to a second 6513 which I only want to use if the first link is down.

Right now I just have a single default route:

ip route 0.0.0.0 0.0.0.0 172.25.1.1

Should I add anything to the second static route?


Thanks.

I have this problem too.
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Jon Marshall Wed, 01/06/2010 - 05:22

jfraasch wrote:

I want to use two static routes for my 3750's.  I have multiple VLANs on the 3750 and I just have a single /30 point to point connection to a 6513.


I am adding a second /30 connection to a second 6513 which I only want to use if the first link is down.

Right now I just have a single default route:

ip route 0.0.0.0 0.0.0.0 172.25.1.1

Should I add anything to the second static route?


Thanks.

Jason

Yes, you can give the second static route a higher AD so it becomes a floating static and will only be used if the first static route is removed from the routing table ie.

ip route 0.0.0.0 0.0.0.0   200   <-- note the 200, that is the AD

However you should then test to make sure that when the first link fails the primary static route is removed from the routing table. WIth a /30 P2P link it should do but if it doesn't then you will need to use IP SLA for tracking the availability of the next-hop.

Jon

jfraasch Wed, 01/06/2010 - 05:26

I guess that was the second part of the question.  How will it know to failover?  If the first link goes down, will it fail to the second?

Jon Marshall Wed, 01/06/2010 - 06:01

jfraasch wrote:

I guess that was the second part of the question.  How will it know to failover?  If the first link goes down, will it fail to the second?

On a P2P link it should do but it's worth checking with ethernet. If for example the ports were configured as L2 switchports and you had L3 vlan interfaces then no the route would not be removed.

On serial P2Ps it defintely would remove the route if the other end went down but with ethernet it is often necessary to track the availability of the next-hop and if it goes down install another route in the routing table.

An alternative approach is to run a dynamic routing protocol such as EIGRP between the 6500 and 3750. Have 2 P2Ps but only run EIGRP on one of them. And have your floating static on the 3750 pointing to the other end of the link that EIGRP is not running on. What happens here is the 3750s receive routes from the 6500 down the link that EIGRP is running on. EIGRP routes will have a lower AD than your floating static at 200 AD and so they will be used. If the link goes down the route(s) are no longer received so the floating static is used.

Note the above would work without a floating static if the EIGRP routes sent to the 3750s were more specific than the default-route ie. you can just have a normal default-route on the 3750 and it won't be used until the more specific routes disappear. If however you are sending the same route down both links you would need a floating static.

There is always more than one way to acheive the same thing and some are easier than others. I believe the 3750 supports IP SLA but have never used it so it would definitely need testing if you decide to use it.

Jon

jfraasch Wed, 01/06/2010 - 06:08

Yep, that is exactly what we have.

Vlan 27 is 172.16.1.2/30

Vlan 30 is 172.16.1.6/30

Ports connected over to the 6513 are access ports.

Issue number one is that I have control and access to the 3750's but not to the 6513's.  I cannot run a routing protocol.

Right now we have the static 0.0.0.0 0.0.0.0 172.16.1.1

If I add second static, I don't think it will work unless I do IP SLA like you are saying.  I will start researching on it.

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