Subject: Re: I-D Action:draft-rosenberg-internet-waist-hourglass-00.txt]

From: [email-masked] (Noel Chiappa)
Date: Tue, 19 Feb 2008 12:22:48 -0500 (EST)

<Apologies that this ia a bit old, but it repeats a - sadly - very common
misperception that is worth correcting yet again.>

    > From: Iljitsch van Beijnum <[email-masked]>

    > If a protocol doesn't need port numbers or a UDP-like checksum (i.e.,
    > either no checksum or a better one)

UDP does provide for packets with no checksum. Read the spec:

  "An all zero transmitted checksum value means that the transmitter
  generated no checksum (for debugging or for higher level protocols that
  don't care)."

(Minor pet peeve: we did blow it very microscopically, IMO; the reserved
value should have been all ones, not all zeros, as all ones could never be a
legitimate output from the checksum-generation step, but that's a minor
quibble.)

	Noel
_______________________________________________
Ietf mailing list
[email-masked]
http://www.ietf.org/mailman/listinfo/ietf

---

From: Marshall Eubanks <[email-masked]>
Date: Tue, 19 Feb 2008 14:34:53 -0500

>   generated no checksum (for debugging or for higher level  

Not AFAICT in IPv6 :

rfc2460 :

       o  Unlike IPv4, when UDP packets are originated by an IPv6 node,
          the UDP checksum is not optional.  That is, whenever
          originating a UDP packet, an IPv6 node must compute a UDP
          checksum over the packet and the pseudo-header, and, if that
          computation yields a result of zero, it must be changed to hex
          FFFF for placement in the UDP header.  IPv6 receivers must
          discard UDP packets containing a zero checksum, and should log
          the error.

There has been discussion recently about relaxing this in UDP  
tunnels, such as AMT.

Regards
Marshall

---

From: Brian E Carpenter <[email-masked]>
Date: Wed, 20 Feb 2008 09:39:25 +1300

On 2008-02-20 08:34, Marshall Eubanks wrote:
...

>           discard UDP packets containing a zero checksum, and should log

Of course, this decision was taken in parallel with the decision to drop
the IP header checksum from IPv6. Nobody was quite ready to 100% trust
the link layer.

   Brian

---

From: Marshall Eubanks <[email-masked]>
Date: Tue, 19 Feb 2008 15:47:42 -0500

> the IP header checksum from IPv6. Nobody was quite ready to 100% trust

And the discussion about dropping this in IPv6 is in the context of  
tunnel encapsulations where the
interior packet has a checksum.

Marshall

---

From: Stefanos Harhalakis <[email-masked]>
Date: Wed, 20 Feb 2008 02:18:36 +0200

> interior packet has a checksum.

But "what is" the interior packet if the udp header is mangled and the ports 
were changed? AFAICT at least the header checksum is required when using 
IPv6.
_______________________________________________
Ietf mailing list
[email-masked]
http://www.ietf.org/mailman/listinfo/ietf