Generating 'Fragment Needed but DF was Set' ICMP & Dummynet

Alexander Motin mav at
Tue Feb 17 02:11:48 PST 2004


I observe a strange thing. When I create dummynet pipe on output router 
interface with lower MTU system stops to generate 'Fragment Needed but 
DF was Set' ICMP in cases when it must. If I create this pipe on 
incoming interface there is no problem.

I check this on many routers under 4.8 and 5.2 FreeBSD.

Is this a bug or feature? :) How pipes can be created leaving ICMP 
generation working?

Alexander Motin

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