[j-nsp] Full BGP table, one provider w/ 2 routers, slow forwarding convergence

[Clarke Morledge]

I am trying to resolve a forwarding convergence problem in our existing 
architecture all doing BGP with full routing feeds with upstream 
providers. In one particular case, I am multihomed with one single 
provider (single AS) with two routers (A and B)  existing in different 
locations for redundancy.

My objective initially is an active/passive scenario, failing over to the 
backup link to this provider in the event of a fiber cut, using BFD to 
signal to BGP a problem. My first thought was to establish one external 
BGP group connecting to neighbor A, sending out my routes without much AS 
prepending and setting a high local preference for incoming routes. A 
second external BGP group connects to neighbor router B, using lots of AS 
prepending for my routes going out, and using a lower local preference for 
routes coming in.

In testing the design, my advertisements going out get updated almost 
immediately with my upstream provider, per looking at their looking glass 
during a "fiber cut." But on my end, even though BGP starts to change 
the preference for the incoming routes fairly quickly, it takes a long 
time to push the changes to the forwarding tables in the PFE.  With the 
full Internet table, I have seen it take up to about 80 to 90 seconds for 
a few selected routes.

My objective was to get the failover to complete in less than 20 seconds. 
Presumably, if I were only handling the default route, the solution would 
be trivial, but at this point I need to keep on receiving the full 
Internet table.

Can I do what I need to do with some sort of BGP multipath load balancing, 
but with keeping my traffic engineering objectives intact?

Below are some config snippets. Thanks for any suggestions/solutions.

Clarke Morledge
College of William and Mary


--------------------------------

Upstream Provider ASN: 65001
Upstream Provider Router A (Primary): 172.16.0.2
Upstream Provider Router B (Backup): 172.16.1.2


[edit policy-options policy-statement bgp-isp-router-b-out]
term local-16 {
     from {
         route-filter 192.168.0.0/16 exact;
     }
     then {
         as-path-prepend "65002 65002 65002 65002 65002 65002 65002 65002 
65002";
         accept;
     }
}

[edit policy-options policy-statement bgp-isp-router-a-out]
term local-16 {
     from {
         route-filter 192.168.0.0/16 exact;
     }
     then {
         as-path-prepend "65002 65002 65002";
         accept;
     }
}
[edit policy-options policy-statement bgp-isp-router-b-in]
term default {
     then {
         local-preference 285;
         accept;
     }
}
[edit policy-options policy-statement bgp-isp-router-a-in]
term default {
     then {
         local-preference 290;
         accept;
     }
}
[protocols bgp]
group isp-router-a {
     type external;
     import bgp-isp-router-a-in;
     export bgp-isp-router-a-out;
     peer-as 65001;
     bfd-liveness-detection {
         minimum-interval 999;
         multiplier 10;
     }
     neighbor 172.16.0.2;
}
group isp-router-b {
     type external;
     import bgp-isp-router-b-in;
     export bgp-isp-router-b-out;
     peer-as 65001;
     bfd-liveness-detection {
         minimum-interval 999;
         multiplier 10;
     }
     neighbor 172.16.1.2;