[e-nsp] Extreme Networks Summit1iTx L3 switch delays ICMP traffic routed through the switch or addressed to the switch

[Mikael Abrahamsson]

On Mon, 1 Sep 2014, Martin T wrote:

> Thanks for all the information! So in case the utilization of tBGTask
> process is less than 90%, all the other IP traffic should suffer as
> well?

No. By default ICMP is slow-pathed, everything else is fast-pathed. ICMP 
can be made fast-pathed on some incarnations i-chipset platforms by 
issuing "disable icmp access-lists". They re-spun the forwardig ASICs back 
in 2004-2005 or so to enable this feature, as the inferno chipset in the 
original design punted all ICMP to CPU, they introduced a system-wide flag 
to disable this behavior. Since the ASIC doesn't have the capability to 
inspect ICMP in fast-path, when you change this flag, you no longer can 
ACL ICMP at all.

If you're running i-chipset devices as routers and have a decent amount of 
flows, I also recommend to "enable ip-subnet lookup" feature. A masksize 
of /20 or so is a balanced approach for Internet use. This helps to not 
deplete the ipfdb and also speeds of convergence after a re-route.

> For some odd reason I didn't observe this. Based on my
> tests(hping and custom-made script utilizing bash UDP and TCP
> sockets), only the RTT of ICMP traffic increased while RTT for example
> for UDP or TCP traffic did not change at the time when CPU utilization
> of tBGTask was <90%.

That is default behavior.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se