[c-nsp] ip tcp adjust-mss

Alexander Arseniev ecralar at hotmail.com
Tue Feb 12 11:02:39 EST 2013

> From: mack.mcbride at viawest.com
> To: moua0100 at umn.edu; 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-to-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).ThanksAlex 		 	   		  

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