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

[Martin T]

Hi,

I have a legacy Extreme Networks Summit1iTx L3 switch(running EW
7.8.4.1), which delays ICMP traffic routed through the switch and ICMP
traffic addressed to the switch while traffic switched through the
switch is not affected. For an odd reason, only ICMP traffic seems to
be affected and not for example TCP or UDP traffic. There is a clear
correlation between high RTT and low CPU utilization(less than 90%) of
tBGTask process. It is always the tNetTask process, which CPU usage
increased and thus forced tBGTask process utilization below 90%.
According to ExtremeWare 7.0 software manual, tNetTask(network stack
task) process is responsible for handling all the software-based
processing of packets including:

1) Packets that cannot be handled by the switch's ASIC because the
forwarding tables do not have entries built in.
2) Packets destined to the CPU for one of the router interfaces.
3) Packets that must be examined or snooped by the CPUPackets detected
for copying to the CPU.

Has anyone seen such behavior before? Why does low CPU utilization of
tBGTask process affect only ICMP traffic? Any suggestions how to see
exactly which traffic causes CPU utilization of tNetTask process to
increase?



thanks,
Martin