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OSPF Advertising Default Route Problem

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1,656 Views
Last Modified: 2012-05-06
Hi,

I am configuring a network with OSPF at the moment. I am trying to build in as much redundancy as possible. So far everything is working very well as planned but I have hit a mind block here.

My main problem centres on the fact I have 2 possible gateways. One, a Bonded SDSL line, is the preferred route. The second is a standard ADSL line for redundancy.

I am using the openospfd implementation of OSPF.

I have 2 routers, 1 connected to each DSL modem. These routers advertise themselves as default gateways to the network. The ADSL router has a higher metric cost than the SDSL router. In practice this worked perfectly. When browsing the internet I was going over the SDSL. I then shut down the SDSL router and my route changed to the ADSL.

The problem is that if the incoming line itself dies, for example the DSL goes out of sync, Router1 (SDSL) is still alive and advertising itself as the preferred gateway. I therefore have no connectivity.

I need to find a way to prevent the advertisement of a default gateway if the box that is advertising has no external connectivity.

This must be possible but I cant think how to do it.

I use both openospf & Quagga on various routers so Im sure I could translate a solution for one system over to the other.

I hope that was not too confusing and I eagerly await any suggestions.

I have attached my ospfd config below for the advertising router.

Kind Regards,

Chris Morgan.
fib-update yes
#redistribute static
redistribute connected
redistribute default
router-id 192.168.0.1
router-priority 3
 
area 0.0.0.0 {
interface fxp0 {
auth-type none
hello-interval 10
router-dead-time 40
}
interface fxp1 {
auth-type none
passive
hello-interval 10
router-dead-time 40
}
 
}

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system administrator
Top Expert 2007
Commented:
> When browsing the internet I was going over the SDSL. I then shut down the SDSL router and my route changed to the ADSL.
Try to do the same, but turn off the _modem_, not the router, tell me if it works.

> This must be possible but I can't think how to do it.
If you mean is it possible with OSPF - yes, but not in your configuration. To do it with 'pure' ospf, the OSPF should be located also on ISP side, on the other end of your DSL modem.

You may however to create a custom script (to be run on each router), that will 'ping' remote host and if it can't see it - just shutdown ospf process and vise versa, if it sees then - start it again. Once OSPF process will be dead, the ospf database will be rebuild and another host will become default router.

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