[c-nsp] slow convergence on edge BGP routers

[Adam Vitkovsky]

Well that's a complex problem 

You can eliminate the egress traffic loss completely by using features like: "prefix independent convergence" to avoid the need for slow FIB programing, "advertise best external" to have a backup path available at the primary AS-EXIT and the local repair capability of "BGP PIC EDGE" to reroute all 530K+ prefixes towards the backup AS-EXIT in several hundreds of microseconds (yup not even a millisecond). 

However on ingress you need to wait till all AS-es connected to your primary upstream get the withdraw and rely it to their customers or other AS- es hanging off of them (and possibly all these folks need to wait some more till they all receive an alternate route from their local ASBRs if a given remote AS or your upstream is not using "advertise best external" feature).

15s is fine if you consider that the default BGP advertisement interval for eBGP sessions is 30s.
Although I have never monitored this or tried in the lab.
-has anyone seen this type of behaviour on a rush network where multiple updates and withdraws take place in a 30s interval do you actually see this update pacing in effect please?
 

adam
> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> jure brkljacic
> Sent: 27 February 2015 01:43
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] slow convergence on edge BGP routers
> 
> Hi,
> 
> We have two bgp routers with full bgp table. All traffic is forced over
> router EDGE1(from EDGE2 and "internal" router).
> 
> When i shutdown the "upstream link" on EDGE1 all the traffic is rerouted to
> EDGE 2 router, but i see 15sec complete outage. (the path the end system
> takes in "internal router" ->>EDGE1->>EDGE2)
> 
> a.) BFD enabled on all interfaces (bgp neighbor is immediately torn down)
> b.) no input queues on EDGE 1 during the convergence
> c.)EDGE routers are ASR1004 with RSP2
> 
> 
> how to minimize the traffic loss?
> 
> 
>       |                           |
>       |                           |
>       |                           |
> +-----+-----+            +-----+-----+
> |              |            |               |
> |  EDGE1 ----------------EDGE2  |
> |              |            |               |
> +----+------+            +--------+--+
>      |                             |
>      |                             |
>      |                             |
>      |                             |
>      |                             |
>      |                             |
>      |                             |
>      |        +----------+       |
>      |        |             |       |
>      |        |             |       |
>      +--------+Router+--------+
>               |             |
>               |             |
>               +----------+
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
---------------------------------------------------------------------------------------
 This email has been scanned for email related threats and delivered safely by Mimecast.
 For more information please visit http://www.mimecast.com
---------------------------------------------------------------------------------------