Solved: Undesized packages occur when VoIP connected

helpdesk · ‎08-24-2008

Hi,

I have a problem.

I use 3560 PoE switches to connect IP phones to our network. When connected, my switch ports start generating undersized packages. If just a regular pc is connected on a similar port these don't occur. Any idea how to solve this problem? Thanks.

Bart van Es

Michael Owuor · ‎08-27-2008

Bart,

UnderSize Frames are described as the total number of packets received that were less than 64 octets long (excluding framing bits, but including FCS) and have a good FCS value.

What you are seeing is due to a limitation in the 3550 ASIC in which 802.1q packets of the length 64-67 bytes are counted as undersized packets even though they are legal packets according to the IEEE standard. This is only an accounting problem and it does not affect data forwarding. In other words, these packets are still forwarded correctly by the switch, and only the stats are wrong. The problem is cosmetic.

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCed73388

Hope this helps.

Regards,

Michael.

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Michael Owuor · ‎08-24-2008

Hi Bart,

For clarification, what specifically indicates that undersized packages are being generated?

Thanks,

Michael.

helpdesk · ‎08-26-2008

Hi Michael,

On a standard configured port undersized packages are registered when a VoIP telephone is connected. When I just connect a PC to the same port these undersized packages do not occur. We use Avaya 1600 phones and as I understood these phones also do something with package sizes.

Bart

helpdesk · ‎08-27-2008

Reference message: Hi Michael,

On a standard configured port undersized packages are registered when a VoIP telephone is connected. When I just connect a PC to the same port these undersized packages do not occur. We use Avaya 1600 phones and as I understood these phones also do something with package sizes.

Bart

-------------------------

Additional info: It occurs on WS-3560 switches. Regards, Bart

Michael Owuor · ‎08-27-2008

Bart,

UnderSize Frames are described as the total number of packets received that were less than 64 octets long (excluding framing bits, but including FCS) and have a good FCS value.

What you are seeing is due to a limitation in the 3550 ASIC in which 802.1q packets of the length 64-67 bytes are counted as undersized packets even though they are legal packets according to the IEEE standard. This is only an accounting problem and it does not affect data forwarding. In other words, these packets are still forwarded correctly by the switch, and only the stats are wrong. The problem is cosmetic.

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCed73388

Hope this helps.

Regards,

Michael.

helpdesk · ‎08-27-2008

Hi,

Michael,

Thanks for your help.

Regards,

Bart

Michael Owuor · ‎08-27-2008

You are very welcome Bart. Have a good day!

Regards,

Michael.