[c-nsp] multipath doesn't work on received default routes?

[Oliver Boehmer (oboehmer)]

Dan Hollis <> wrote on Friday, November 18, 2005 1:26 AM:

> I'm receiving default routes from 3 upstreams, but ios doesn't seem to
> want to multipath the default route. Only one default route is ever
> used, verified by looking at the outbound counters on the interfaces.
> [...]
> sh ip bgp 0.0.0.0 verifies that the routes are valid, but sh ip ro
> 0.0.0.0 shows only one route ever being entered into the table.
> 
> #sh ip bgp
> BGP table version is 1730946, local router ID is 2xx.xxx.xxx.xx6
> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> internal Origin codes: i - IGP, e - EGP, ? - incomplete
> 
>     Network          Next Hop            Metric LocPrf Weight Path
> *  0.0.0.0          6x.xxx.xxx.xx7           0    200      0 xx9 i
> *>                  1xx.xx.xxx.1                  200      0 xxxx1 i
> *                   1xx.xxx.xxx.2                 200      0 xxxx2 i
> 
> #sh ip bgp 0.0.0.0 0.0.0.0
> BGP routing table entry for 0.0.0.0/0, version 1212671
> Paths: (7 available, best #3, table Default-IP-Routing-Table)
>    Not advertised to any peer
>    xx9
>      6x.xxx.xxx.xx7 from 6x.xxx.xxx.xx7 (2xx.xxx.xxx.xx0)
>        Origin IGP, metric 0, localpref 200, valid, external
>    xx9, (received-only)
>      6x.xxx.xxx.xx7 from 6x.xxx.xxx.xx7 (2xx.xxx.xxx.xx0)
>        Origin IGP, metric 0, localpref 100, valid, external
>    xxxx1
>      1xx.xx.xxx.1 from 1xx.xx.xxx.1 (1xx.xx.xxx.1)
>        Origin IGP, localpref 200, valid, external, best
>    xxxx1, (received-only)
>      1xx.xx.xxx.1 from 1xx.xx.xxx.1 (1xx.xx.xxx.1)
>        Origin IGP, localpref 100, valid, external
>    xxxx2
>      1xx.xxx.xxx.2 from 1xx.xxx.xxx.2 (2xx.xxx.xx.x1)
>        Origin IGP, localpref 200, valid, external
>    xxxx2, (received-only)
>      1xx.xxx.xxx.2 from 1xx.xxx.xxx.2 (2xx.xxx.xx.x1)
>        Origin IGP, localpref 100, valid, external
>    Local, (received-only)
>      2xx.xxx.xxx.xx3 from 2xx.xxx.xxx.xx3 (2xx.x.xxx.x4)
>        Origin IGP, metric 0, localpref 100, valid, internal

You can see that none of the paths is considered "multipath" since they
have been received from different AS (AS path is different).
http://www.cisco.com/warp/public/459/25.shtml#bgpmpath describes the
algorithm and the criteria.
If you run an IOS with the fix for CSCea19918 (BGP: need to do multipath
with different as-paths), you can enable the hidden BGP knob "bgp
bestpath as-path multipath-relax" to load-share across those paths..

	oli