High CPU load on 6509E VSS

[WillemBont_2]

One of our 6509E VSS setups running SXI6 is experiencing high CPU load.

It has just been upgraded from SXH5 and its CPU load has always been on the high side.

But now it has become worse:

CPU utilization for five seconds: 93%/19%; one minute: 92%; five minutes: 92%

11   250050244 149143658       1676 47.35% 47.25% 47.28%   0 ARP Input

85    13429160  28384463        473  2.31%  2.33%  2.31%   0 ARP HA

146     7103368  19496858        364  4.79%  6.57%  6.95%   0 SNMP ENGINE

312     7930112  33286908        238  1.11%  1.27%  1.30%   0 IP Input

#sh ip arp sum

859 IP ARP entries, with 19 of them incomplete

# sh ip traffic | b ARP shows 47826 ARP requests over 1 minute interval.

Many of our hosts attached to this switch use ARP to check the bonding. We have reduced the ARP interval

on these hosts from 400 ms to 1 sec and that resulted in some lower CPU load. But not as much as we expected.

In another DC we have a similar setup, but that VSS (SXI5) has only 12% CPU load for ARP processes.

We have ruled out an ARP attack.

We do not use proxy-arp anywhere.

Does anyone know what could cause this problem and if changing IOS to another version (maybe SXH8?) will solve anything?

Thanks in advance,

Willem

[Derek Zhang]

You probably can use NetDr to have a clear understanding what packet(s) hit th CPU.

I believe downgrade/upgrade may not resolve your issue since these are packets punt to CPU, but no matter on which version.

You can find NetDr at https://supportforums.cisco.com/docs/DOC-15608

[WillemBont_2]

Thank you Dazhi Zhang,

We have been monitoring as follows:

monitor session 1 type local source cpu rp both

destination interface gigabitethernet bla

no shutdown

Is this netdr the same thing?

And what is impact on the cpu when we invoke netdr debugging?

Again, thank you for your much appreciated input :-)

Willem

[Derek Zhang · Accepted solution]

Yes, NetDr will do the same thing in some situation you dont have the SPAN capability e.g. a remote switch which you are not able to have SPAN.

the command you used should also have the cpu packets caputre.

And netdr will not impact the cpu/system performance which has 4K packet buffer FIFO.