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Re: [MBONED] [Fwd: I-D Action:draft-eubanks-chimento-6man-00.txt]

Here are my comments. Draft text comes first and indented and my comments follow. 


The argument made by the draft authors is that since multicast
packets already have a UDP header with a checksum, there is no
additional benefit and indeed some cost to nodes to both compute and
check the UDP checksum of the outer (encapsulating) header.  However,
Consequently, IPv6 should make an exception to the rule that the UDP
checksum MUST not be 0, and allow tunneling protocols to set the
checksum field of the outer header only to 0 and skip both the sender
and receiver computation.
It is worse than that for AMT. Since the control packets are encapsulated in an IGMP packet format. There is an IGMP checksum performed as well, then on top of that encapsulated in UDP, with the UDP checksum performed there too.
So please note that the burden might be less in the control-plane, but it is less necessary to do UDP checksum as well in this case. I think you shouldn't deprecate the behavior in the spec, but outline how double check-summing is occurring in this case. 


 3.  Exception for lightweight tunneling: Amend IPv6 to allow a 0
       value in the UDP checksum field for leightweight tunneling
protocols which allows them to bypass any checksum computation in 
       the outer header if the inner packet is protected.  Rules for
       usage in this case must be developed.
Be more clear that the encapsulator does not have to compute a checksum on packet forwarding and the decapsulator, because the UDP checksum is 0, does not need to check the checksum.
4. Another possibilty is to allow an exception for the AMT protocol 
       only.  This may seem undesirable, but it would restrict the
       implementation of a zero checksum UDP header over IPv6 only to
the AMT endpoints. Any misdelivered packets (i.e. arriving at a 
       non-AMT endpoint) would simply be discarded.
There are other protocols coming that will use UDP encapsulation. It is becoming popular to use UDP so you get LAGs to work inside of the tunnel as well as an easier way to get through firewalls. 

One example is LISP.


  Others on the mailing list have pointed out other issues with
changing the IPv6 specification to allow a checksum of 0 on the outer 
   packet header.  In particular, Matt Mathis points out that some
   tunneling devices ignore the DF bit and fragment silently.  This
would allow two fragmented UDP packets to be spliced together and be 
   decapsulated and forwarded by a tunnel endpoint.
But can we make a mention that link-layer CRC, ECC, and checksum do find high percentage of link errors, so there is another level of protection we can rely on. Please state that somewhere in the spec. 


 Magnus Westerlund proposed some restrictions on using a UDP header
   checksum of 0.  These are:
Since Magnus is being referred to multiple times in this draft, I suggest you put his contact info at the end. 


 2.  The tunneling protocol and implementation must not use
       fragmentation of the inner packets being carried.


I would change "must not" to "should not".


   We would suggest the following elaborations of the above
   restrictions, if a change in the IPv6 specification moves forward:

   o  An inner IPv4 packet with a UDP checksum equal to 0 must not be
      tunneled.

   o  Non-IP inner packets must have a CRC or other mechanism for
      checking packet integrity.

   o  Other tunneling protcocols that use the UDP checksum equal to 0
MUST NOT be tunneled themselves, even if more deeply encapsulated 
      packets have checksums or other integrity checking mechanisms.
o We would recommend that general protocol stack implementations do NOT implement this change. The exception should remain restricted 
      to devices serving as endpoints of the lightweight tunneling
      protocol adopting the change.

   In addition, we would recommend that a security analysis be done in
   order to assess whether any new vulnerabilities are introduced by
   such a change.
This is to strong of language. You create more work for hardware implementations to adhere to this. Which means they will just ignore it. 

I would change all occurences of "must" to "should".

Thanks,
Dino

On Feb 24, 2009, at 5:21 AM, Brian Haberman wrote:


All,
Here is the draft that proposes to loosen the UDP checksum rule for IPv6. I would appreciated if discussions of this draft occur on the 6MAN mailing list (ipv6 at ietf.org). 

Regards,
Brian


-------- Original Message --------
Subject: I-D Action:draft-eubanks-chimento-6man-00.txt
Date: Mon, 23 Feb 2009 10:45:01 -0800 (PST)
From: Internet-Drafts at ietf.org
Reply-To: internet-drafts at ietf.org
To: i-d-announce at ietf.org
A New Internet-Draft is available from the on-line Internet-Drafts directories. 

	Title           : UDP Checksums for Tunneled Packets
	Author(s)       : M. Eubanks
	Filename        : draft-eubanks-chimento-6man-00.txt
	Pages           : 7
	Date            : 2009-02-23

We address the problem of computing the UDP checksum on tunneling
IPv6 packets when using lightweight tunneling protocols.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-eubanks-chimento-6man-00.txt

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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Internet-Draft.

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