[Bug 220351] Path MTU discovery works only after resetting an internal interface MTU (mpd5, ng_nat, ipfw)

[Herbert J. Skuhra]

Eugene Grosbein skrev:
> 
> 02.07.2017 22:11, Herbert J. Skuhra пишет:
>> Eugene Grosbein skrev:
>>> 
>>> 02.07.2017 21:03, Herbert J. Skuhra wrote:
>>>> Skype for Business (S4B) on Mac OS X 10.12.6 (Beta5) is actually
>>>> trying to connect over IPv4. The connection fails until I lower MTU to
>>>> 1440. After resetting MTU to 1500 and restarting S4B it connects fine
>>>> for a while ('route -n get' default shows 1500). I use 'set iface
>>>> enable tcpmssfix' in mpd5.conf and I've tried:
>>>> 
>>>> - set iface mtu and set link mtu/mru/mrru in mpd5.conf
>>>> - set scrub ... max-mss in pf.conf
>>> 
>>> Please show output of ifconfig command for external ng interface.
>> 
>> ng0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metric 0 mtu 1440
>> inet6 fe80::XXX:XXXX:XXXX:XXXX%ng0 prefixlen 64 scopeid 0x7 
>> inet XX.XX.XX.XX --> XX.XX.XX.YY netmask 0xffffffff 
>> nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
> 
> 'set iface enable tcpmssfix' in mpd.conf should be enough for you.
> 
> Are you sure you have it in right point of the config?
> This is critical for it to take effect. Please see mpd.conf.sample for example.
> 
> Doesn't mpd complain of this command to its log?

No.

> Make sure you have 'log +iface +iface2' command in your mpd.conf,
> restart mpd5 and scan its log for 'tcpmssfix'.

mpd: [B1] IFACE: Connecting tcpmssfix

But when I disable IPv6 on my network everything is working... even
without tcpmssfix enabled.

Instead of enabling ipv6cp in mpd5 I've also tested with an IPv6 tunnel
from HE... same issue. :-(

--
Herbert