First Ping timeout

[Chris Shaw]

Hi,

I know there has already been a couple of threads on this but rather than add my question to the bottom of one of those I thought I would try afresh.

We have an 857W connected to the internet via ADSL. All works very well, however if I ping from an attached PC the first one always times out. If i ping from the router (ping www.google.com source 192.168.18.1) I get !!!!! every time. Back to the PC and 'Request timed out' on the first.

The only way I have been able to resolve this is by using no ip cef. It then works as expected, first ping and all. The problem is after much reading, it is not ideal to disable cef.

I would be very grateful for any suggestions.

Thanks,

Chris

[Chris Shaw]

Good morning Hobbe,

Thanks for your comment. Yes, I understand about ARP lookup however it doesn't explain why when CEF is disabled the problem goes away. In addition, when you ping directly from the router the first ping goes through without hitch even when you using the internal interface as the source.

Interestingly, last night I went to a friends house who has a company provided Cisco 857. We were able to telnet into it and discovered that CEF had been disabled! Looks like someone else got stuck on this one too.

Thanks,

Chris

[Peter Paluch]

Hi Hobbe,

You are right about the ARP but we have ruled it out as an issue here: when a PC is pinging the router itself, the packets are lost only the very first time, and afterwards, subsequent pings are successful. What is strange is that pinging an outside address behind the router almost always causes the first packet to get lost, and that is certainly not caused by any ARP process.

Best regards,

Peter

[Chris Shaw]

Hello All,

Firstly, thanks to Peter for all of his help. I am still stuck with this problem. Does anyone have any idea what is causing this issue. I would greatly appreciate any suggestions.

Thanks,

Chris

[Phillip Remaker]

OK, I poked around internally and the only way you should lose a packet is during the initial ARP request.  But it seems that the ARP cache is populated in this case. (True?)

I see when you do back-to-back pings (VERY CLOSE TOGETHER) you do not have the problem, but if you wait a few seconds than then ping, the first packet is always lost.

So the question is:  Can you measure how long that gap is?  Is it 3 seconds? 5 seconds?  10 seconds?  30 seconds?

It seems that some kind of cache is timing out, causing a packet loss while that cache is repopulated.  If there is a consistent time after which the first ping fails, that would be a hint.  It may be an interaction with cef and some other feature, since cef itself should not have such a problem.

Using a more feature-rich ping that Windows (like Linux, or some 3rd party utility), you could use the "-i" inetrval command.  You can increase the interval until you have constant failure, and that will expose the expiration interval you are up against, if it is cache expiration related.

[skarthic · Accepted solution]

Chris,

This is a bug as mentioned in the following link

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCti13229

Affects 12.4T(14)

Has been fixed in 12.4T(15) but is releasing in march 11

Try downgrading to T13 as the bug doesnot affect the T13 version

Please rate to let me know the answer helped.

Thank you

Karthic.R.

[Chris Shaw]

Karthic,

Thank you. I can't tell you how long I've been pulling my hair out on this one.

Thanks to everyone that contributed.

Kind Regards,

Chris

[Chris Shaw]

All,

I just wanted you to all know that I have upgraded the router to c850-advsecurityk9-mz.124-15.T15.bin and the issue has now been fixed.

Thanks to everyone for their help.

Chris