route converge time

Greg Foletta greg at
Mon Nov 23 00:00:16 UTC 2015

Would be helpful if you let us know what platform you're running on.
Assuming a Cisco, make sure next-hop-tracking not disabled (enabled by
default on modern IOS), then at "BGP Prefix Independent Convergence", so
your BGP process isn't walking the entire RIB to see which next-hops it
needs to change.

Greg Foletta
greg at
+61 408 199 630

On 23 November 2015 at 05:12, Colton Conor <colton.conor at> wrote:

> What types of routers are you currently using?
> On Sat, Nov 21, 2015 at 7:44 AM, Baldur Norddahl <
> baldur.norddahl at>
> wrote:
> > 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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