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Date:      Sun, 2 Jul 2017 22:23:18 +0700
From:      Eugene Grosbein <eugen@grosbein.net>
To:        "Herbert J. Skuhra" <herbert@mailbox.org>
Cc:        freebsd-net@FreeBSD.org
Subject:   Re: [Bug 220351] Path MTU discovery works only after resetting an internal interface MTU (mpd5, ng_nat, ipfw)
Message-ID:  <59590FE6.7030109@grosbein.net>
In-Reply-To: <87a84myitf.wl-herbert@mailbox.org>
References:  <bug-220351-2472@https.bugs.freebsd.org/bugzilla/> <bug-220351-2472-lCDWr8PCgb@https.bugs.freebsd.org/bugzilla/> <87r2xzaw30.wl-herbert@mailbox.org> <87bmp3x7eu.wl-herbert@mailbox.org> <59590064.1040700@grosbein.net> <87a84myitf.wl-herbert@mailbox.org>

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

Can you send the log to me, it you still have the problem?



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