OSPF Advertising Default Route Problem

Posted on 2009-02-10
Last Modified: 2012-05-06

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-priority 3

area {

interface fxp0 {

auth-type none

hello-interval 10

router-dead-time 40


interface fxp1 {

auth-type none


hello-interval 10

router-dead-time 40



Open in new window

Question by:koollkidd
    1 Comment
    LVL 27

    Accepted Solution

    > 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.

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    Highfive Gives IT Their Time Back

    Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

    We recently endured a series of broadcast storms that caused our ISP to shut us down for brief periods of time. After going through a multitude of tests, we determined that the issue was related to Intel NIC drivers on some new HP desktop computers …
    Transparency shows that a company is the kind of business that it wants people to think it is.
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor ( If you're looking for how to monitor bandwidth using netflow or packet s…

    779 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    16 Experts available now in Live!

    Get 1:1 Help Now