Re: ip crc check

To: iperf-users --at-- dast.nlanr.net
Subject: Re: ip crc check
From: Jon Dugan <jdugan --at-- ncsa.uiuc.edu>
Date: Mon, 8 Mar 2004 16:12:48 -0600
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> >Hello all,
> >
> >I have a question regarding to the IP packet crc check.
> >
> >I would like to check the incoming IP packets for errors. 
> >I think that iperf does not work on the IP packet level and gives no
> information about the IP CRC check.

  The IP checksum is checked inside the IP stack; when a packet fails a
  checksum it is discarded and an error counter is incremented.  So if Iperf
  receives the packet it passed the CRC check.

  It is important to note that the IP checksum is not a packet checksum but a
  checksum of the IP header.

> >Does anyone know, if there is a software availiable to get these
> information ?  

  This is system dependent.  On a BSD type system netstat -s -p ip will show
  you the relevant information, it is listed under "bad header checksum".
  netstat -s on Linux doesn't appear to list this.  I don't know anything
  about how this is reported under Windoze.

  Chapter 8 of TCP/IP Illustrated, Volume 2 by Wright and Stevens covers the
  BSD implementation of this.


Jon
-- 
Jon Dugan             |  Senior Network Engineer, NCSA Network Research
jdugan --at-- ncsa.uiuc.edu  |  269 CAB, 605 E Springfield, Champaign, IL 61820
217-244-7715          |  http://www.ncsa.uiuc.edu/~jdugan/

References:
- ip crc check
  - From: Mitch Kutzko

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