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Subject: Re: [Bug 220351] Path MTU discovery works only after resetting an
 internal interface MTU (mpd5, ng_nat, ipfw)
To: "Herbert J. Skuhra" <herbert@mailbox.org>, freebsd-net@FreeBSD.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>
From: Eugene Grosbein <eugen@grosbein.net>
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Date: Sun, 2 Jul 2017 21:17:08 +0700
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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.