First Ping request timed out

[pandasang]

Hi Experts,

I have a strange issue where the first ping always times out, but the following goes through fine.I have Cisco877 and connection to the internet is fine. I connect a PC to one of the FastEther ports and I am able to ping the router without any issues. However, the moment I ping an external website i.e. ping www.google.com the first ping request fails. after that the following request come through quickly.

Has anyone come across this before?

Thanks,

[burleyman]

This is not an ARP "problem" it is just how it works. If you try and ping something and there is not a ARP entry for that it will drop the ping packet and not even send it, instead it will send out an ARP request and once it gets a reply the rest of the pings go through. So it is not that the ARP request or reply is taking too long and you are not seeing the first ping be successful it is that the first ping is dropped on purpose so a ARP request could be sent in its place. Again this is not a problem but normal behavior, because when you ping the same address again right after all pings come back successful because there is now an ARP entry. If you were always losing the first ping even on the second try then there could be a problem with the ARP cache but that is not the case here.

Mike

[krishna3010]

may be the arp slow on the other side where the server is

[burleyman]

It is NOT that it is slow it IS that the first ping is NOT even sent.....it IS dropped so that an ARP request can be sent in its place. Again this is normal behavior. If the first ping was ALWAYS dropped that could indicate a problem but that is not the case here. I think you may be looking for a problem where one does not exist.

Mike

[burleyman]

I just re-read the post and he states when he ping from the PC the first time he gets this    .!!!!  4 out of 5, the frist ping is dropped. He than says if he trys the ping again from the PC all 5 ping now work and he sees this   !!!!!  5 out of 5. He did not say it always drops the first ping from the PC.

Mike

[burleyman]

I actually just found this as well.

https://supportforums.cisco.com/message/3070853

Hope this helps

Mike

[cadet alain]

Hi Burley,

If we follow your reasoning then from a pc with arp cache empty for destination hrdware address the first ping is not sent and it gives . for first ping?

then if I flush my arp cache and do a ping to a destination from my windows box how come all my icmp echoes are all sent?

It's because default timeout is 4 seconds on windows xp box and 2 seconds on Cisco IOS and the arp request/reply takes longer than 2 secs but less than 4?

Can you give me more details about this please?

Regards.

[burleyman]

It is not the ARP on your PC but the ARP on the first hop router. If the first hop router does not have the ARP entry then the Router drops the ping and sends out an ARP request. Now it may also be any router on the way to the destination I am not 100% that it is only the first hop router.

Mike

[cadet alain]

Hi Mike,

Thanks for clarification.

regards.

Alain.

[pasole001]

I have a similar issue with IOS version 12.4(15)T14.Turned out to be something related to dynamic Nat. For me - every first packet does not leave the outside interface of the router. When I use static nat everything works normally. I changed the ios version and now everything works fine.

[Dregathar]

Thanks, ilia, for your hint about IOS version. Change of IOS resolved the same problem.