CSM packet loss

[Zarahelll]

Good afternoon

I´m having a problem/issue with my CSM. I have a WS-X6066-SLB-APC - Version 4.2(1), installed on a 6500, and for a while now whenever I ping the VIPs (vservers) I detect some packet loss (In 10.000 ping packets, I loose around 1%), and higher response times; If I ping the reals I see no issues, only with the L3 behind the CSM.

Any ideas of what the problem might be?

Best regards

[Fabrizio Pedracini]

Hi,

when pinging the vservers the request/response will be handled by the cpu and they will get low priority. So if you send a large amount of packets you may get occasional loss of reply because the cpu is busy with higher priority tasks.

hope this helps,

Fabrizio

[Zarahelll]

Fabrizio

Thank you for your reply, but I don´t believe that´s the issue.

I don´t have traffic or processes that justify a high CPU usage percentage, but I still performed a quick test: I´ve opened 2 windows with 2 sessions to the switch and I ran another 100.000 pings test on one window, while showing (

repeatedly) the processes cpu history for the last 60 seconds simultaneously. The CPU never got any higher than 20% usage during the pings...and I still detected around 1% packet loss.

Any other ideas?

[Cesar Roque]

Hi,

The CSM processes echo requests in it's slow path, so CSM will only process up to 600pps of

ICMP traffic at which point it will drop any packets in excess of 600pps.

That could be the reason.

[Zarahelll]

Cesar

Thats very probably the reason.

I would like to confirm though...do you know of a way to extend the value? Increase the limit of 600 pps? I would like to increase this value and then see if it keeps loosing packets.

[Fabrizio Pedracini · Accepted solution]

Hi,

as Cesar correctly pointed out, the pps limit is 600 and it's hardcoded. You can check "show mod csm X tech slowpath" to see the slowpath counters divided by protocol and also you can grep for 'Slowpath' in the output of "show mod csm X tech proc 1"

#show mod csm 3 tech-support processor 1 | i Slowpath

Packets Drop: Slowpath limit exceeded    0          0          0        

Packets Repeat: Slowpath limit exceeded  0          0          0        

Packets Slowpath                         5949       0          0        

Packets Repeat and Slowpath              0          0          0        

Fabrizio

[Zarahelll]

Cesar and Fabrizio...that´s it

I´ve confirmed the drops with command you posted above.

Thank you for your support.

Btw, just one final question: what other processes are run by the CSM slowpath?

[Fabrizio Pedracini]

slowpath will handle all IP traffic directed to VLAN interfaces, ICMP to the vservers, ARP traffic, all the health monitoring traffic (probes), FTP control channel traffic and HSRP.

Fabrizio

[Zarahelll]

Thank you very much Fabrizio.

Do you know of a link with an official Cisco paper or document containining that information?

[Zarahelll]

Anyone?

I´ve tried to find the official Cisco Documentation describing the processes run by the slowpath, the 600 pps limitation, etc and I didn´t find anything.

Does anyone know where I can find the Cisco paper describing all that?

[Fabrizio Pedracini]

I could not find any pointer for you regarding the 600pps.

Here is explained what is handled in slow path and also that pps limit is 4 times bigger on the server VLAN:

http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/ServerFarmSec_2.1/5_CSM.html#wp1096165

cheers,

Fabrizio

[Zarahelll]

Many thkx