North American Network Operators Group
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Re: IP Fragmentation

  • From: Colin Alston
  • Date: Wed Aug 20 14:57:45 2008
On 2008/08/20 08:04 PM [email protected] wrote:
On Wed, 20 Aug 2008 21:43:44 +0530, Glen Kent said: 
Do transit routers in the wild actually get to do IP fragmentation
these days? I was wondering if routers actually do it or not, because
the source usually discovers the path MTU and sends its data with the
least supported MTU. Is this true?


Hypothetically true.  Unfortunately, enough places do bozo firewalling and drop
the ICMP Frag Needed packets to severely limit the utility of PMTU Discovery.


Well obviously, ICMP is only used by hackers to DDoS you. Everyone knows that, especially all the banks. It's even more important to obliterate PMTU discovery when you're using HTTPS - for security, you know.

Sorry, I spent the better part of today bashing my head against the wall trying to fix MSS and PMTU issues somewhere which was being aggravated by the tragic programming of Linux l2tpns package...