[nsp] limits to CEF per-packet load sharing?

[Oliver Boehmer (oboehmer)]

> On Thu, 13 Feb 2003, Edward Henigin wrote:
> 
> > > I think you'll find the limit for the max paths IOS will 
> load share across 
> > > varies from release to release.  I know we're running 
> some that max out at 
> > > 6, and some at 8...and the default, IIRC, is 4.  If 
> you're using OSPF (as 
> > > we are on our backbone) you'll have to raise the 
> max-paths explicitly.  We 
> > 
> > They'll be staticly routed.
> 
> I suspect there's still a limit.  Maybe someone from cisco 
> will chime in.

Yes, you're right. While CEF (in theory) could load-balance across 16
adjacencies (the loadsharing bucket has 16 entries, as shown in "show ip
cef <prefix> internal"), the maximum number of equal cost paths we can
put in the RIB is six (no matter which routing protocol, incl. static).
This limit was increased to eight in 12.0(14)S/ST and 12.1(8)E.

So if you want to load-balance evenly across 10 T1s, you need MLPPP to
create some bundles and load-share across those. Or you can use a c7500,
put all 10 T1s on a single VIP and use distributed Multilink
(http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newf
t/120t/120t3/multippp.htm and
http://www.cisco.com/warp/public/793/access_dial/ppp_11044.html), which
supports link bundling of up to 40 T1s given a fast VIP (VIP4/VIP6). Of
course: For redundancy purposes I would not put all the T1s on a single
VIP, rather distribute them across multiple VIPs and create multiple
distributed Multilink bundles and CEF-load-balance across those.
 
	oli