[c-nsp] ebgp load balancing using maxiumu-paths TCAM impact on Sup720-3BXL?

[Kevin Hodle]

Hi Peter,

  Another option for load balancing outbound traffic in your scenario
would be to do some netflow analysis on your upstream ports and have a
look at what the top destination ASNs your outbound traffic is flowing
toward. Using this data, you can construct as-path ACLs which you can
utilize in your inbound route-map on each upstream BGP session to set
a higher local-preference  for 'preferred' routes on each session (ie
routes from ASXXX get a local-preference 1 higher than your standard
upstream route local-preference), and accept the rest of the full
table on each session with your normal local-preference. Using your
netflow analysis you should be able to achieve a fairly equal traffic
split (as you will be able to see what % of your total outbound
traffic is going to which ASNs, use this data to come up with an
approximated 50/50 outbound traffic split) and you will still have
redundancy in place for all routes if one of the sessions drop. It
would take a little more effort than simply turning on multi-pathing,
but in your scenario it might be more ideal as you won't have to worry
about 3bxl TCAM constraints with this method.

Cheers,
Kevin Hodle

On Wed, May 20, 2009 at 9:40 PM, Peter Kranz <pkranz at unwiredltd.com> wrote:
> Setup is as follows; 2 edge routers, each with a BGP session receiving full
> routes to the same provider router. The provider is load balancing inbound
> traffic to our AS nicely, 50/50 between the edge routers.. I would also like
> to load balance the outbound traffic.. I've considered adding 'maximum-paths
> 2' to install the two equal paths, but an concerned about FIB TCAM impacts.
> Will adding this command cause each equal cost route to take one additional
> TCAM entry, i.e. full routing table x 2 > 524k TCAM limit = EPIC meltdown?
>
>
>
> Current FIB TCAM:
>
> L3 Forwarding Resources
>
>             FIB TCAM usage:                     Total        Used
> %Used
>
>                  72 bits (IPv4, MPLS, EoM)     524288      285506
> 54%
>
>                 144 bits (IP mcast, IPv6)      262144           5
> 1%
>
>
>
> Peter Kranz
>  <http://www.UnwiredLtd.com> www.UnwiredLtd.com
> Desk: 510-868-1614 x100
>
> Mobile: 510-207-0000
>  <mailto:pkranz at unwiredltd.com> pkranz at unwiredltd.com
>
>
>
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