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Re: [RRG] The use of UDP in LISP



On 11 dec 2007, at 5:49, Shane Amante wrote:

So? If we put in the spec that you MUST assign a /29, /28 or what have you to an ETR and all ITRs automatically use that entire address range, they'll simply have to do it or it won't work.

You might certainly be able to say MUST, but that doesn't mean everyone will configure ITR/ETR's that way.

If the spec mandates that the mapping protocol caries /28 prefixes and that ITR round robin flows over the addresses within those /28s, then I'm pretty sure ETR operators will do it that way unless this makes them so upset they force vendors to make ITRs that don't conform to the spec. I.e., laziness then means using the /28.

How about this:

For IPv4 locators there is no checksum issue and we use UDP.

For IPv6 locators there is the checksum issue, the overhead is already much larger than with IPv4 but the good parts are that we have the flow label and there isn't an ossified installed base yet. So for IPv6 locators we skip the UDP header.

It's true that there is much discussion on the philosophy of flow labels, but as long as there is one, it's stable for the same flow for at least a decent amount of time (doesn't have to be forevever, changing it at minute scale or longer won't be too problematic for our purposes) it's good enough. And since we control the operation of ITRs we can mandate that a flow label is present.

And obviously with IPv6 it's trivial to have a larger number of addresses per ETR if that's helpful.

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