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TomS_
Git-r-done
MVM
join:2002-07-19
London, UK

TomS_ to Bigpaddy_Irl

MVM

to Bigpaddy_Irl

Re: Routing publics over ospf network

OSPF (and BGP) router ID should always be based on something like a loopback interface address, which is typically a /32.

This helps in terms of stability because loopback interfaces are usually implemented in software and are always up as long as the router is booted. And if the router isnt booted, well, OSPF is your least concern at that point in time.

If you dont have a loopback interface then OSPF is likely to pick and choose from the other interface IPs that are available, and if one of those interfaces goes down that would cause a router-id change, then its got to drop all neighbors and re-establish with a new router-id. This will cause disruption for traffic that would otherwise just pass through that router.

Semaphore
Premium Member
join:2003-11-18
101010

Semaphore to Rhaas

Premium Member

to Rhaas
How many routers in the area? Is convergence time not a problem?

Rhaas
Premium Member
join:2005-12-19
Bernie, MO

1 edit

Rhaas

Premium Member

My network?
Currently 29 OSPF speaking routers. I had to collapse back down to a single area due to topology.

Convergence is generally sub 5 seconds on link failure.

Semaphore
Premium Member
join:2003-11-18
101010

Semaphore

Premium Member

Hmmm so about the same as here then... Followed all of MT's recommendations for Best Practices. They could see that there was a problem but not what was causing it.

Rhaas
Premium Member
join:2005-12-19
Bernie, MO

Rhaas

Premium Member

said by Semaphore:

Hmmm so about the same as here then... Followed all of MT's recommendations for Best Practices. They could see that there was a problem but not what was causing it.

What is the issue you are having?
We are fighting an issue where routes are not propagating correctly if there is redundant link. I read that there is an issue with their ecmp calculations in 5.X so I have been upgrading all of the routers to 6.7. I still have one that is at 4.17 that puked on 6.7 so I am getting the hardware to replace it.

Semaphore
Premium Member
join:2003-11-18
101010

Semaphore

Premium Member

If one of the main links flap I rarely end up with a route in the forwarding table that was not the route that packets are actually following, so asymmetrical routing via main and secondary links, but when looking at the forwarding table at each end it *looks* OK. Sound similar ?

I moved one POP and the uplinks to 6.7 a few weeks ago for test. Everything else it 5.26. Maybe I need to upgrade my routers.

Rhaas
Premium Member
join:2005-12-19
Bernie, MO

Rhaas

Premium Member

That sounds right with the ecmp calculations.

My temporary fix has been to install a rb750gl that does nothing but talk ospf to a router and reboot itself every 15 minutes.

What I found is any router in the network rebooting will clear the issue I was having.

Semaphore
Premium Member
join:2003-11-18
101010

Semaphore

Premium Member

I had to reboot a couple to clear the problem.... but not necessarily the DR/BDR.... usually those at the ends of the affected links, but not always.

Rhaas
Premium Member
join:2005-12-19
Bernie, MO

Rhaas

Premium Member

Mine is just a router hanging off a router towards the middle of the network.

I've had issues with 6.7 & X86 routers. Had another one that I upgraded started rebooting and losing interfaces.