[c-nsp] Outbound drops on 6748

[Dean Smith]

We have some web security appliances connected via 1Gb/s copper  to 6748
Line cards in a Cat 6513 with Sup720. The appliance manufacturer assures us
the appliances can cope with traffic well above 800Mb/s (The traffic is
always equal in both directions)

 

We have previously seen traffic levels > 500Mb/s for a period without any
issue. However more recently we have seen elevated response times to the
appliances as the bandwidth approaches 400Mb/s. Investigations show we're
seeing outbound drops now as we approach those speeds. We have qos enabled
on the chassis but these particular ports have up till now been left at
default queue setting. All the traffic is in queue 0 which currently only
has 50% of the queues. We have now amended that to 90% but will have to wait
until the next peak in traffic to judge the impact.

 

However I'm a little unsure why we previously saw no issue @ 500Mb/s but do
now @ 400Mb/s. Nothing has changed on the appliances - however we did remove
some other redundant 6148A cards to allow the switch to operate in full DFC
mode. I don't have outbound errors/drops from before the cards were removed
but response times certainly didn't show the increase.

 

Is it likely/possible that when operating in CFC mode the chassis/CFC was
effectively buffering the packets better before hitting the switchport.but
now they're arriving directly via DFC the individual port buffers are
struggling ?. If that theory doesn't hold water..any other suggestions ?

 

What bi-directional throughput is reasonable to expect from a 6748 port ?

 

(If it makes any difference the chassis build has 1x original ACE, 3xFWSM,
2x6704 ,1x6708 and 2x6748+ 1 xSup720. All the line cards now have DFC 3B (or
3C for 6708) where appropriate)

 

Thanks

Dean