In that case multihop BFD (if supported on both sides) would really help. Regards, Jeff
On Nov 28, 2015, at 11:37 AM, Matthew Petach <mpetach@netflight.com> wrote:
One thing I notice you don't mention is whether your BGP sessions to your upstream providers are direct or multi-hop eBGP. I know for a while some of the more bargain-basement providers were doing eBGP multi-hop feeds for full tables, which will definitely slow down convergence if the routers have to wait for hold timers to expire to flush routes, rather than being able to direct detect link state transitions.
Matt
On Sat, Nov 21, 2015 at 5:44 AM, Baldur Norddahl <baldur.norddahl@gmail.com> 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 0.0.0.0 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