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Re: Flow label - the problem



On 24-apr-2005, at 5:28, Erik Nordmark wrote:

However, a good way to enforce this is to disallow overlap between ULIDs and additional locators. So if a host sees prefixes A and B, it forms four addresses:
A::ULID
A::locator-for-B
B::ULID
B::locator-for-A

I wouldn't say that this is forbidding the applications from selecting the ULID. Instead I view this as a different way to carry information to the receiver to help it disambiguate the packets (and what rewriting is needed before passing the packets to the ULP); you are effectively carrying that information in the IP address fields.

Right, and these are big and many bits in them can generally be filled in by the host so that could work very well.


Another way is to allow more than a single shim6 association at one time between two hosts,

I don't understand how this would work.
Whether or not there is a single shim6 association isn't the key issue.
The issue is that the receiver will need to handle packets with the same locator pair in them, where some of them need to have those locators replaced with different ULIDs before passing them to the ULP.
To do this there has to be something in the packet that can distinguish the packets. Could be by effectively carrying the disambiguating information in the address fields as you suggest above, the flow label, or some separate context tag carried in the packet. And this extra information can be skipped when the receiver doesn't have to rewrite the address fields.

I was trying to address the issue on a conceptual level with the above and this:


or to have transport sessions with different ULIDs within a single association. In this case there are four ways to determine the right ULID set:

The difference is that either you send letters addressed to different people living at the same address in different envelopes, which has the upside that there doesn't have to be any demux info in the letter itself but the downside that there must be more demux info on the envelope and more envelopes, or you send all letters to one address in one envelope and demux the letters when they come out of the envelope.


For TCP/UDP/SCTP/RTP the port numbers can be used to demux, and the flow label can take the place of the port numbers as an optimization.