pmtud + ipnat RELENG_6_2 appears to be broken

[Stephen Clark]

Alexey Karagodov wrote:

> is there any progress? 
>
> just one "me too" 
>
> this problem appeared for me when i try to use vlan over lagg ( to em 
> NICs ) 
>
> thanx 
> kernel: vlan301: discard oversize frame (ether type 800 flags 3 len 
> 1514 > max 1510) 
>
>
>
> 2007/7/13, Chuck Swiger <cswiger at mac.com <mailto:cswiger at mac.com>>:
>
>     On Jul 12, 2007, at 1:38 PM, Stephen Clark wrote:
>     >> The MTU is actually defined in reference to a network segment such
>     >> as  an "ethernet collision domain", and applies to all machines
>     >> sending  traffic to that segment.  If the MTU is really 1280,
>     >> nobody else  should be sending larger packets, and the drivers
>     >> will drop any  larger packets they receive and generate the
>     >> appropriate ICMP error....
>     >
>     > First thanks for responding but thats the problem,
>     > this did't generate an icmp when the packet was dropped.
>     >
>     > kernel: rl0: discard oversize frame (ether type 800 flags 3 len
>     > 1514 > max
>     > 1294)
>     >
>     > This message did not result in any icmp packet.
>     >
>     > I was running tcpdump looking for them.
>
>     Taking a quick look at ether_input() in src/sys/net/if_ethersubr.c
>     suggests that you are right-- if the incoming packet exceeds the MTU
>     being set, the input errors count for that interface is incremented,
>     but no ICMP_UNREACH_NEEDFRAG is generated even if DF flag is set.
>
>     You might file a PR and see whether you can get Andre or one of the
>     other networking gurus interested in fixing this.  Or maybe I'll give
>     it a try myself if I can get some free time....  :-)
>
>     --
>     -Chuck
>
>
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>
No progress - still being discussed on freebsd-net mailing list as:

Re: 6.2 mtu now limits size of incomming packet

Steve

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