untraceable ping drops over ethernet WAN link

Unanswered Question
Jun 28th, 2007

We have an issue with pings (very small amount < 1% ) that are dropped on an ethernet WAN link, but we can't see them anyware else.

No errors on the interface,not QOS related, no failures in the huge buffers and the fysical line is also tested and good.

Does anyone have any ideas for other places to check for errors or something like that, that relate to these ping drops.

P.S.: any size of ping gets dropped ,small or large

I have this problem too.
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mohammedmahmoud Thu, 06/28/2007 - 01:27


Does the packet drop occur when doing back-to-back direct ping, or is the pinged IP a multiple hops away.


Mohammed Mahmoud.

dvangyzeghem Thu, 06/28/2007 - 01:42

We have ping drops in both cases , but we only checked for all possible causes (known for us) on the back-to-back ping.

dvangyzeghem Thu, 06/28/2007 - 01:59

Hi Mohammed,

The average utilization of this link is 25% in and out , with peaks to 50% , but we have the drops all the time and we cannot see them as output drops on the interface.



mohammedmahmoud Thu, 06/28/2007 - 02:14

Hi Dimitri,

Ok, please try to ping multiple destinations on this interface (direct hops, and multiple hops), and on other interfaces if available, and feedback us with the pattern, and by the way how is the router CPU doing.


Mohammed Mahmoud.

dvangyzeghem Thu, 06/28/2007 - 02:29

Hi Mohammed,

Thank you very much for your help so far.

Do you have ant suggestions or ideas as to were to look on the router for these drops.

I think that is impossible to find a pattern in this case , because the ping drop occur very irregular something 1000 ping pass without dropping , sometimes up to 5 drop.

But i will try to ping at the same time back-to-back and one hop away and let you know if the drops occur simultanious.

The CPU on both routers is fine : less than 40%.


dvangyzeghem Thu, 06/28/2007 - 04:52

hi Mohammed,

I tried to find a possible scenario to do the ping test you asked , but i think i cannot ping these interfaces from anywhere else due to the routing (VRF's), only back to back.

What i did do is ping the loopback of one of the routers from the management station , so i pass the link also , and this did not miss any pings while the back - to - back ping that ran simultanious missed some.

I already did this test before and then both pings missed some but maybe because of a different issue.

Remark : the pings from the managment station did not go as fast as the back-to-back ping.

Pavel Bykov Thu, 06/28/2007 - 02:22

You don't see them as output drops? Well, then do you see them as input drops? Input drops can be related to high hw utilization.

How do you know that it drops?

dvangyzeghem Thu, 06/28/2007 - 02:55

Hi slidersv,

there are no input drops either.

I mean that ping does not succeed.

I don't know why, i can't see anything in the queues , buffers or on the interface (no drops , no errors ) just after the missed ping.

Do you know any other places or commands to check for missing packets?




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