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Manual administrative distance with static routes



if I have the following routes in place:

ip route serial0/0 1

ip route bri0/0 2

If the serial is up, it will be routed out the serial. If the serial goes down, will this route out the bri interface until the serial comes back up?



10 Replies 10


That is correct.


Thanks Mick. Much appreciated.


Yes. This technique is called "floating" static routes.


This worked well on a spoke router when the serial interface went down. The problem is now on the "hub". If the serial line on a spoke router goes down, it routes to the ISDN. Now, with this in the hub router:

ip route 10.x.128.1

ip route 10.x.129.0 Serial0/0 1

ip route 10.x.129.0 BRI2/1 2

ip route 10.x.130.0 Serial0/0

Even though the serial line on the spoke router is down and it is routing over the ISDN, the hub router does not know to switch to route over BRI2/1. Is there a way to have a router know that if it cannot reach a destination through a static route then try another?


As long as you're using HDLC or PPP, when the serial line goes down on one side, it will go down on the other and this should still work.

If you're using Frame Relay, use point-to-point sub-interfaces instead of point-to-multipoint interfaces. This could cause one side to be up while the other side is still down.

What I don't understand is why you don't have a route for 10.x.130.0 pointing out your BRI2/1 interface.


Thanks Mick.

These routers are connected directly to the internet with ISP routers between our endpoints. So, when the link goes down on a spoke, the hub's serial is still up "talking" to the next hop (ISP) and the other spokes (HDLC is used).

Also, 10.x.130.0 with point out BRI2/2 for backup,10.x.131.0 will point out BRI2/3 for backup (etc).

Each spoke will have a dedicated BRI interface for backup purposes to the hub. Perhaps I should look into point-to-point sub-interfaces for this as well?

Thanks for the info,


Misunderstood your scenario.

Since you have interim routers, you'll need a routing protocol to determine if the other side is down.

Or, you could tunnel and route through that, but there is overhead/fragmentation associated with tunnels.


Sorry, I should have painted a better picture from the start. I am using IPSEC and tunnels to each spoke and routing all traffic through these tunnels (15 different tunnels). 3 spokes will have a dedicated ISDN line to the hub for backup. If there is no way at the hub to determine if a peer/spoke is down while using static routes, then I will need to look into a routing protocol.

Thanks for the pointers....


If you're using tunnel interfaces, they should go down when they can't reach their peer and allow you to use floating static routes to your ISDN backup.


I see what you mean now. I am using IPSEC tunnels, not tunnel interfaces and I understand how floating static routes will work with tunnel interfaces since it depends of the status of the interface (to float or not). Now I will test/check IPSEC with a tunnel interface to see how much extra overhead there is and if everything will still work.

Thanks Mick...

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