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Conference turris::digital_unix

Title:	DIGITAL UNIX(FORMERLY KNOWN AS DEC OSF/1)
Notice:	Welcome to the Digital UNIX Conference
Moderator:	SMURF::DENHAM

Created:	Thu Mar 16 1995
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	10068
Total number of notes:	35879

9000.0. "lo0 MTU 16384" by HGOVC::SIUKEUNGLEE () Fri Feb 28 1997 11:39

    Hi,
    
    I found some suggestion for network tunning are to increase the local
    loopback MTU size. What are the usage of setting the local loopback MTU to 
    16384 ? The default MTU for lo0 is 1500. 
    
    	#ifconfig lo0 ipmtu 16384
    
    Welcome any suggestion !
    
    Thank!
    
    David.

T.R	Title	User	Personal Name	Date	Lines
9000.1		SMURF::MENNER	it's just a box of Pax..	`Fri Feb 28 1997 19:33`	4
	Some software uses local loopback as a form of inter process communication. Since the loopback is not a real network interface you can increase the MTU. Larger MTUs decrease the change of fragmenting TCP/UDP data.
9000.2	changing the defaults?	VIRGIN::SUTTER	Who are you ??? - I'm BATMAN !!!	`Mon Mar 03 1997 03:54`	7
	If this is generally a good idea (and many system check utilities like UNIcensus suggest that this parameter is beeing raised) why don't we change the default to a reasonable value? Regards, Arnold
9000.3		SMURF::MENNER	it's just a box of Pax..	`Mon Mar 03 1997 07:56`	3
	Re: .2 good idea!
9000.4	I give you the permission to do it ...!... ;-)	VIRGIN::SUTTER	Who are you ??? - I'm BATMAN !!!	`Mon Mar 03 1997 09:54`	7
	Ok, let's do it then. Who to contact/involve in such a major decision?-) Regards, Arnold
9000.5		DECWET::ONO	Software doesn't break-it comes broken	`Wed Mar 26 1997 14:57`	12
	The mtu recommendation of 16384 was posted in the NetWorker conference a while back. A customer recently upgraded to DU 4.0b, and this value caused his local IP throughput to drop dramatically. Setting mtu to 15000 improved things, and he says his current value of 3072 gives the best performance. I'm trying to figure out why the customer sees this behavior. Regards, Wes Ono NetWorker Engineering
9000.6		DECWET::ONO	Software doesn't break-it comes broken	`Wed Mar 26 1997 14:59`	3
	additional info re: .5 The 16384 value worked fine for 3.2g.
9000.7	get a tcpdump trace	SMURF::DUSTIN		`Thu Mar 27 1997 08:59`	7
	The best way to find out what's going on is to get a tcpdump trace of the traffic on lo0. Starting in the V4.0 release, you can now run tcpdump on the loopback device, which makes the problem much easier to diagnose. John
9000.8		DECWET::ONO	Software doesn't break-it comes broken	`Thu Mar 27 1997 20:29`	7
	John, We're working on this (as I mentioned in response to your mail). Thanks for the assist. Wes