MS Group Policy Failure - ICMP size too small on router??

[cybrsage]

http://support.microsoft.com/kb/816045

When you use Group Policy to determine whether a link is fast or slow, fast links may be incorrectly flagged as slow links.

This problem may occur when a network that you are trying to detect a slow link to is configured to control the size and flow of Internet Control Message Protocol (ICMP) packets. For example, if a router allows for only ICMP ping packets that have a size of 1,024 bytes, the slow-link detection feature may flag the connection as a slow link. This is because the router discards ICMP packets that are larger than 1,024 bytes. If the router discards the packet because it exceeds the allowed size, fast links may be reported as slow links.

According to Microsoft, the default ICMP ping packet size of 2048 is used.

Microsoft recommends changing every single Windows machine's ICMP size...but my customer would rather just change the router.  Any suggestions on how to do this?

It is a 2821 router, running 12.4(24)T4, using MLPPP to bundle two T1s.

[cybrsage]

My googe-fu is failing me...I have found nothing so far.  Anyone have any ideas?

[cadet alain]

Have you tried pinging this router with such packet size?

Here on a 3725  platform pings with such a size were not dropped.

[cybrsage]

Thank you for the reply.  As soon as I posted my last statement, Google took up the challenge and provided me with some

hits on my searches, one of which was on this very forum (although quite old).

https://supportforums.cisco.com/people/diego%40ats-corp.com?referring_site=kapi

There is one more piece in my puzzle, which I think is what is killing me.  There is a firewall between the router and the rest of the network.  This is preventing the adjust-mss from working properly on the LAN side of the router.

Suffice it to say I am going to have to tell the Windows administrator to make a registry edit and MTU size change on each Windows machine on the inside of the firewall.  Either that, or put a MS BDC at the site (not a bad idea, really).

[cadet alain]

Hi,

This is preventing the adjust-mss from working properly on the LAN side of the router

MSS is for TCP what has it got to do with ICMP?

Regards.