route converge time

Colton Conor colton.conor at
Sun Nov 22 18:12:50 UTC 2015

What types of routers are you currently using?

On Sat, Nov 21, 2015 at 7:44 AM, Baldur Norddahl <baldur.norddahl at>

> Hi
> I got a network with two routers and two IP transit providers, each with
> the full BGP table. Router A is connected to provider A and router B to
> provider B. We use MPLS with a L3VPN with a VRF called "internet".
> Everything happens inside that VRF.
> Now if I interrupt one of the IP transit circuits, the routers will take
> several minutes to remove the now bad routes and move everything to the
> remaining transit provider. This is very noticeable to the customers. I am
> looking into ways to improve that.
> I added a default static route to provider A on router A and did
> the same to provider B on router B. This is supposed to be a trick that
> allows the network to move packets before everything is fully converged.
> Traffic might not leave the most optimal link, but it will be delivered.
> Say I take down the provider A link on router A. As I understand it, the
> hardware will notice this right away and stop using the routes to provider
> A. Router A might know about the default route on router B and send the
> traffic to router B. However this is not much help, because on router B
> there is no link that is down, so the hardware is unaware until the BGP
> process is done updating the hardware tables. Which apparently can take
> several minutes.
> My routers also have multipath support, but I am unsure if that is going to
> be of any help.
> Anyone got any tricks or pointers to what can be done to optimize the
> downtime in case of a IP transit link failure? Or the related case of one
> my routers going down or the link between them going down (the traffic
> would go a non-direct way instead if the direct link is down).
> Thanks,
> Baldur

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