pmtud problem

[Stephen Clark]

Alexander Motin wrote:

>Stephen Clark wrote:
>  
>
>>>>if the pc sends a packet of 1460 bytes with the DF bit set shouldn't the
>>>>freebsd 4.9 system
>>>>send back an icmp dest unreachable - fragmentation needed and DF bit 
>>>>set?
>>>>        
>>>>
>>>Are you blocking icmp with a firewall filter?
>>>
>>>      
>>>
>>Good  question - but the answer is no. The other interesting fact is 
>>when I drop the mtu on
>>the gre to 1412 I do see the icmp messages.
>>    
>>
>
>Are you using any dummynet shapes? There is ancient bug in dummynet, 
>which leads to not sending of ICMPs when shape used on outgoing interface.
>
>  
>
Hi Alexander,

I had run into that problem before, in this case I am seing a icmp for 
1420 mtu for the gre
 on the 4.9 side but the tun0 interface that pppoe is 1492 to allow for 
the ppp wrapper and I just
read that the gif when using ipv4  doesn't handle pmtud - that I think 
is my real problem.

Steve

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