[c-nsp] ip tcp adjust-mss

Mack McBride mack.mcbride at viawest.com
Thu Feb 14 12:44:35 EST 2013

Reality is UDP matters.

LR Mack McBride
Network Architect

-----Original Message-----
From: Randy [mailto:randy_94108 at yahoo.com] 
Sent: Wednesday, February 13, 2013 11:14 PM
To: Mack McBride
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] ip tcp adjust-mss


What corner cases??
This thread was about TCP:(ip tcp adjust-mss)not UDP!
As, has been already pointed out:

To OP:

Put in the little-effort required to UP MTU's on your physical-interfaces to support your services and as already-mentioned, design/re-design your network accordingly.

"ip-mtu and mtu(physical-int) are two very different things.

--- On Tue, 2/12/13, Mack McBride <mack.mcbride at viawest.com> wrote:

> From: Mack McBride <mack.mcbride at viawest.com>
> Subject: Re: [c-nsp] ip tcp adjust-mss
> To: "Alexander Arseniev" <ecralar at hotmail.com>, "moua0100 at umn.edu" 
> <moua0100 at umn.edu>, "cisco-nsp at puck.nether.net" 
> <cisco-nsp at puck.nether.net>
> Date: Tuesday, February 12, 2013, 9:31 AM There are always corner 
> cases.
> That's why I said most.
> LR Mack McBride
> Network Architect
> From: Alexander Arseniev [mailto:ecralar at hotmail.com]
> Sent: Tuesday, February 12, 2013 9:03 AM
> To: Mack McBride; moua0100 at umn.edu;
> cisco-nsp at puck.nether.net
> Subject: RE: [c-nsp] ip tcp adjust-mss
> > From: mack.mcbride at viawest.com<mailto:mack.mcbride at viawest.com>
> > To: moua0100 at umn.edu<mailto:moua0100 at umn.edu>;
> cisco-nsp at puck.nether.net<mailto:cisco-nsp at puck.nether.net>
> > Date: Mon, 11 Feb 2013 16:19:35 -0800
> > Subject: Re: [c-nsp] ip tcp adjust-mss
> >
> > Most UDP should not hit the MTU limitation.
> > The common ones that come to mind are streaming
> audio/video and DNS.
> >
> > LR Mack McBride
> > Network Architect
> >
> Wrt "streaming audio/video" - it depends on client/server combo.
> I recently saw an issue with RTSP video streaming from repubblica.it 
> website using Samsung Galaxy RSTP client.
> If UDP video packets are fragmented due to too small MTU in the path, 
> video does not play at all.
> And DNS is somewhat invalid example since when DNS reply does not fit 
> into 512 bytes, then DNS server will set a Truncated bit in the 
> packet, forcing client to use TCP.
> http://serverfault.com/questions/348399/force-forwarder-dns-requests-t
> o-tcp-mode No one uses 512B MTU (apart from miltary who use even 
> smaller MTU) and DNS over UDP would not be experiencing issues due to 
> too small MTU because own DNS payload limit is smaller than smallest 
> real MTUs out there (except military as I mentioned).
> Thanks
> Alex
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