UPD checksumming for Digital Unix Nameserver

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From: 	Ray "The Dragon" Lauff[SMTP:ray at thunder.ocis.temple.edu]
Sent: 	08 May 1996 12:10
To: 	Alpha Mailing List; gurus at thunder.ocis.temple.edu; John Center
Cc: 	pulakr at cableol.net
Subject: 	SUMMARY: UPD checksumming for Digital Unix Nameserver

First off, thanks for all the replies.

It would appear that Digital Unix indeed does do UDP checksums by default.
The checksum is across the header and contents of each UDP packet sent
across the network and is required by several RFCs.

You can use the netconfig(8) tool if you have it, which will display the
state of several kernel networking settings.  I obtained netconfig from:

ftp://ftp.std.com/customers3/src/network/netconfig.tar.gz

It compiled easily on DU 3.2.  If you don't want to use netconfig, you can
use dbx to examine the appropriate variable as follows:

--
root> dbx /vmunix
dbx version 3.11.8
Type 'help' for help.

(dbx) p udpcksum
1
----

If for some reason you want to turn it off (why...I don't know...) you can
use: 
    echo 'assign udpcksum=0' | dbx -k /vmunix /dev/mem

As Chris Jankowski said in his email: 

"Not checking checksums on received packets was a hack to squeeze last
drop of performance from an overloaded CPU.  The rationale given was that 
the networks no longer corrupt packets or that the higher layer of 
protocols will do it. (:-))."


The following people were helpful in their responses:
    Kevin Oberman <oberman at nersc.gov>
    Stuart Davidson <dav at mas.eurocontrol.be>
    Chris Jankowski <chris at lagoon.meo.dec.com>
    Dan Riley <dsr at lns598.lns.cornell.edu>
    Phil LAwrence <philip at uvo.dec.com>
    Matt Thomas <thomas at lkg.dec.com>

Thanks again folks!

Ray
-- 
Ray Lauff : ray at thunder.ocis.temple.edu : (215) 204-5678 : Temple University