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Static Routing Problem with Backup line

hi,

I have a problem. In the picture i have implement IPSec VPN through Routers A, D (Backup Link). The second picture is more detailed showing the same network. I have primary link between E and F through Leased Line. When leased line goes down, Router_E and Router_F sends traffic through IPSec Tunnel (A-D).

Routing is made by Static Routes and Default Routes. Router E and F have those commands:

ip route 0.0.0.0 0.0.0.0 "IP through Leased Line"
ip route 0.0.0.0 0.0.0.0 "IP through Local Router(A, D)" 254

The Problem is with Router_D. The Routing Table of Router_D is showing in the picture. When Leased Line goes down, Router_E sends traffic (for exemple to Router_D) through IPSec Tunnel. When Router_D receives that packet, dοn't know if the leased line is down so tries to reply to Router_E through Router_F and Leased Line, because of Static Route showing in the picture. Router_F sends back to Router_D the packet (default route) and two Routers (D, F) exchange the packet until TTL expires.

If i set to Router_D:

Router_D(config)# no ip route 10.10.41.0 255.255.255.0 fa 0/1

The network works fine with the condition that Leased Line is down.

If Leased Line is up, i must enter the command to Router_D:

Router_D(config)#ip route 10.10.41.0 255.255.255.0 fa 0/1

The same problem would have Router_A with Router_F, but there is no problem because Router_A is not necessary to know where network 10.10.20.0 /24 is in real world.

Is there something that will tell Router_D that leased Line is Down ?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Static Routing Problem with Backup line

Hi John,

I would say, using SLA tracking would be a way to go.

Try doing this:

1. Configure a loopback interface with a distinguished ip address (say, L.L.L.L

2. Configure on router D the following:

ip route L.L.L.L 255.255.255.255

3. Configure SLA Tracking, by ping L.L.L.L.

link: http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html#wp1071672

Example:

ip sla monitor 1

   type echo protocol ipIcmpEcho L.L.L.L source-ipaddr
   exit

ip sla monitor schedule 1 life forever start-time now

track 123 rtr 1 reachability

4. Now track the routes that need to be removed based on L.L.L.L's reachability as follows:

ip route 10.10.41.0 255.255.255.0 track 123

Basically what happens here is:

If L.L.L.L is reachable, the route "ip route 10.10.41.0 255.255.255.0 " stays in the config indicating Leased Line is up. As soon as leased line is down, Router D should not be able to reach L.L.L.L, so SLA fails and the above route is removed from the config. As soon as leased line comes back up, the route is introduced back.

Hope this helps you.

Regards,

Praveen

3 REPLIES

Re: Static Routing Problem with Backup line

Hi John,

I would say, using SLA tracking would be a way to go.

Try doing this:

1. Configure a loopback interface with a distinguished ip address (say, L.L.L.L

2. Configure on router D the following:

ip route L.L.L.L 255.255.255.255

3. Configure SLA Tracking, by ping L.L.L.L.

link: http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html#wp1071672

Example:

ip sla monitor 1

   type echo protocol ipIcmpEcho L.L.L.L source-ipaddr
   exit

ip sla monitor schedule 1 life forever start-time now

track 123 rtr 1 reachability

4. Now track the routes that need to be removed based on L.L.L.L's reachability as follows:

ip route 10.10.41.0 255.255.255.0 track 123

Basically what happens here is:

If L.L.L.L is reachable, the route "ip route 10.10.41.0 255.255.255.0 " stays in the config indicating Leased Line is up. As soon as leased line is down, Router D should not be able to reach L.L.L.L, so SLA fails and the above route is removed from the config. As soon as leased line comes back up, the route is introduced back.

Hope this helps you.

Regards,

Praveen

New Member

Re: Static Routing Problem with Backup line

So you are saying that this are the steps that i must follow (with two questions):

1. L.L.L.L can be 10.40.5.1 of Router_E ?

2. Router_D(config)#ip route 10.40.5.1 255.255.255.255 fa 0/1

3.=>

    

     Router_D(config)# ip sla monitor 1

     Router_D(config-sla-monitor)# type echo protocol  ipIcmpEcho 10.40.5.1 {source-interface  fa 0/1 of router_D or source-ipaddr IP of fa 0/1 of Router_D }?

     Router_D(config)# ip sla monitor schedule 1 life  forever start-time now

     Router_D(config)# track 123 rtr 1 reachability

4.  Router_D(config)#ip route 10.10.41.0 255.255.255.0 fa 0/1 track 123

Packet tracer supports SLAs to test it first there ?

New Member

Re: Static Routing Problem with Backup line

The answer to my question in "NO". Packet Tracer don't support SLAs, but i think i 've got the point !

I hope it works.

Many Thanks,

John

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