On Wed, Jul 28, 2010 at 03:55:44PM -0500, George, Wes E IV [NTK] wrote:
> [[WEG]] I refer you to Bert Manfredi's message
> http://www.ietf.org/mail-archive/web/ipv6/current/msg12042.html.
> The lack of a checksum is why I'm generally resistant to the idea
> of preserving immutability of this field in all or in part - while
> the RFC says it must be, in practical application, a single bit
> error ruins that assumption.
I guess it depends on the application. If the checksum failed, the
packet would be tossed. If the result of the flow label being
corrupted is that the packet is tossed, then the application is
still OK. For example, this would be OK for the transport nonce
application, or using the flow label to find the right layer 3 queue
(if it goes to the wrong queue, there will be no corresponding layer
3 flow, so the packet will be tossed).
> There's no way to be sure that it's
> immutable within an AS, let alone across multiple ASes, so any
> implementation that relies on the intermediate networks not touching
> it (or worse, an implementation that "fiddles" with it and then
> somehow resets it to the original value on egress) is doomed to
> failure.
Note, you can check if people are changing it using traceroute, by
comparing the values in the quotation in the ICMPv6 packet. The
idea is similar to this:
http://www.wand.net.nz/~mluckie/pubs/icmp-pam07.pdf
Last time I checked (which was a couple of years ago), I couldn't
find anyone who was messing with the flow label in-flight. I still
have the code, so I could check what today's network is doing, if
anyone is interested.
David.
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