[c-nsp] NPE-G1 PPS limitations

[Łukasz Bromirski]

Hank Nussbacher wrote:

>> Yea, I would expect that.  I don't understand all of the
>> architechtural issues on the 7200 series in great detail, but it seems
>> that either the PCI bus that line cards use isn't really up to doing
>> GigE, or the controllers on the PA-GE doesn't scale well.
>> The router I saw this on originally had it's primary ingress interface
>> on the NPE and primary egress interface on the PA-GE.  When we swapped
>> a low-traffic interface on the NPE with the PA-GE, we suddenly saw our
>> packet loss drop to nothing.  So I can say with pretty much 100%
>> confidence that local to the NPE will scale much better than the
>> PA-GE.
> Have others found this as well?  So far we have used the builtin GE ports 
> on the G1 and have not seen problems.  We are planning on adding a 4th GE 
> port via a PA-GE and had not seen any documentation about the limitations 
> you mention.

Because of the way PA-GE is connected to the bus, and the way GE
ports on a NPE-G1 are connected to it's separate bus to CPU, you'll
get drastically different performance.

For the GE ports on NPE-G1 you can expect around 470kpps at 64B, for
the traffic going from/to GE port on NPE-G1 to C7200-I/O-GE it's
close to 380kpps at 64B, and going from/to PA-GE it's only around
120kkps at 64B. That'll depend on features, IOS train and the traffic
characteristics of course but those are the baselines for empty
config with CEF and 12.1 train. 12.2S and latest 12.4(15)T rebuilds
should get better performance in the same scenario.

PA-GE to PA-GE traffic maxes out at around 160kpps at 64B with NPE-G1
and NPE-400 - so it's not limitation of CPU engine but a bus
limitation.

Please note, PA-GE was designed "for connectivity" before VIP4 was
released for 7500 so it's pretty old linecard.

-- 
"Don't expect me to cry for all the     |               Łukasz Bromirski
  reasons you had to die" -- Kurt Cobain |    http://lukasz.bromirski.net