Packet Loss Issue - Simple Fix?

Unanswered Question
Sep 13th, 2009

We have a packet loss issue when pinging from a switch to another switch. We believe this packet loss issue may be the cause of a customer complaint.

In doing some testing, I see the packet loss issue, but as soon as I enable debugging, it goes away. What's going on here?

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Sending 50, 2000-byte ICMP Echos to 68.115.X.Y, timeout is 2 seconds:

With debugging off:

Success rate is 38 percent (19/50), round-trip min/avg/max = 16/23/48 ms

With debugging on:

Success rate is 100 percent (50/50), round-trip min/avg/max = 16/25/60 ms

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davidhvoss Sun, 09/13/2009 - 12:27

Here's the debug we are running:

access-list 155 permit icmp any host 68.115.X.Y log

access-list 155 permit icmp host 68.115.X.Y any log

debug ip packet 155 detail

scottmac Sun, 09/13/2009 - 14:55

Please post a SH INT for the affected interface(s); a SHOW BUFFERS might be useful as well.

Packet drop / loss is usually either congestion, as seen by the transmitter, {or | which causes} queuing timeouts.

The congestion can be the receiver's inability to catch the traffic being pushed to it. This happens a lot when you have asymmetrical bandwidth (one end is a T1, the other is a 56K DDS or Frac T1, for example).

Leo Laohoo Sun, 09/13/2009 - 16:46

Debug enabled and you have zero packet loss? I smell an IOS bug. What's the IOS you are using?

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