route converge time

Matthew Petach mpetach at
Sun Nov 29 01:20:20 UTC 2015

Or, better yet, apply a REJECT-ALL type policy
on the neighbor to deny all inbound/outbound
prefixes; that way, you can keep the session
up as long as possible, but gracefully bleed
traffic off ahead of your work.


On Sat, Nov 28, 2015 at 3:46 PM, Jürgen Jaritsch <jj at> wrote:
> Hi,
> Why you not simply shut down the session upfront (before you turn down the link)?
> Best regards
> Jürgen Jaritsch
> Head of Network & Infrastructure
> ANEXIA Internetdienstleistungs GmbH
> Telefon: +43-5-0556-300
> Telefax: +43-5-0556-500
> E-Mail: jj at
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> -----Original Message-----
> From: Baldur Norddahl [baldur.norddahl at]
> Received: Sonntag, 29 Nov. 2015, 0:39
> To: nanog at [nanog at]
> Subject: Re: route converge time
> Hi
> The IP transit links are direct links (not multihop). It is my impression
> that a link down event is handled with no significant delay by the router
> that has the link. The problem is the other router, the one that has to go
> through the first router to access the link the went down.
> The transit links are not unstable and in fact they have never been down
> due to a fault. But we are a young network and still frequently have to
> change things while we build it out. There have been cases where I have had
> to take down the link for various reasons. There seems to be no way to do
> this without causing significant disruption to the network.
> Our routers are 2015 hardware. The spec has 2M IPv4 + 1M IPv6 routes in FIB
> and 10M routes in RIB. Route convergence time is specified as 15k
> routes/second. 8 GB ram on the route engines.
> Say transit T1 is connected to router R1 and transit T2 is connected to
> router R2.
> I believe the underlying problem is that due to MPLS L3VPN the next hop on
> R2 for routes out through T1 is not the transit provider router as usual.
> Instead it is the loopback IP of R1. This means that when T1 goes down, the
> next hop is still valid and R2 is unable to deactivate the invalid routes
> as a group operation due to invalid next hop.
> I am considering adding a loopback2 interface that has a trigger on the
> transit interface, such that a shutdown on loopback2 is triggered if the
> transit interface goes down. And then force next hop to be loopback2. That
> way our IGP will signal that the next hop is gone and that should
> invalidate all the routes as a group operation.
> Regards,
> Baldur

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