North American Network Operators Group

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Re: MTU of the Internet?

  • From: Kevin A. Smith
  • Date: Thu Feb 05 14:55:46 1998

At 12:18 PM 2/5/98 -0600, Phil Howard wrote:
>Marc Slemko writes...
>> First, I _really_ doubt the web server set the DF bit.  It is almost
>> certainly the OS, probably trying to do path MTU discovery.
>> If there is a smaller MTU in the middle, and someone is filtering ICMP
>> can't fragment errors then yes, you will have trouble with PTMU discovery.
>> The fix is to not blindly filter ICMP.  Increasing the client MTU won't
>> fix this.
>Agreed that one should not blindly filter ICMP.  However not all filter
>tests don't support discriminating individual ICMP types.  Ascend is one

Why not? You have the options to use IP filters which are fairly limited,
or generic filters where you can specify more details of the filter.