[15031] in North American Network Operators' Group
Re: MTU of the Internet?
daemon@ATHENA.MIT.EDU (Kevin A. Smith)
Thu Feb 5 14:58:05 1998
Date: Thu, 05 Feb 1998 11:13:11 -0800
To: Phil Howard <phil@charon.milepost.com>
From: "Kevin A. Smith" <kevin@ascend.com>
Cc: nanog@merit.edu
In-Reply-To: <199802051818.MAA02782@charon.milepost.com>
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
>example.
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.
Kevin
