Subject: Switch of UDP-Checksum

From: Peter Sevenich <[email-masked]>
Date: Fri, 9 Mar 2001 08:42:50 +0100 (MET)

Hi,

I like to switch of the UDP-checksummechanisum for realtime-data-transmission on 
narrowband links.
This was possible in the old UDP (IPv4) definition. I think in IPv6 it's not 
longer possible. Is that right or is there a way to switch it of ?

Peter

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++                                                                   
+ Peter Sevenich                                                    +
+ FGAN/FKIE/KOM                                                     +
+ Neuenahrer Str. 20                                                +
+ D-53343 Wachtberg-Werthhoven                                      +
+ Germany                                                           +
+ Phone   +49-228-9435-317                                          +
+ Fax     +49-228-9435-685                                          +
+ e-mail  [email-masked]                                          +    
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From: Steve Deering <[email-masked]>
Date: Sat, 10 Mar 2001 11:20:32 -0800

At 8:42 AM +0100 3/9/01, Peter Sevenich wrote:
>I like to switch of the UDP-checksummechanisum for realtime-data-
>transmission on narrowband links.
>This was possible in the old UDP (IPv4) definition. I think in IPv6 it's
>not longer possible. Is that right or is there a way to switch it of ?

Peter,

That's right, the UDP checksum is not optional when UDP is run
over IPv6.  The reason is because IPv6 does not have its own
header checksum, so the upper layers (UDP, for example) must provide
their own corruption-detection for any IP header fields they rely
on for their correct operation.  In the case of UDP, that detection
is accomplished through the inclusion of the IP "pseudo-header" in
the UDP checksum.

By the way, it is also a bad idea to turn off UDP checksums when using
IPv4, because then you lose the ability to detect corruption of the
UDP port numbers and length field.  (I presume you don't care about
detecting corruption of the UDP payload, or else you wouldn't be asking
this question.)

There was a proposal called UDP-lite which allowed for checksumming of
the UDP header plus IP pseudo-header only, excluding some or all of the
UDP payload.  I don't recall what the status of the proposal is.

Steve