Foo over UDP

Posted Oct 2, 2014 4:59 UTC (Thu) by luto (guest, #39314)
In reply to: Foo over UDP by Fowl
Parent article: Foo over UDP

Is it?

The number 4 could refer to IP protocol 4, which is ipip (in the same numbering system in which TCP is 6) or to IPv4.

If it's IPIP, then does 4 mean that the UDP payload is to be treated as an IPIP payload? If so, then would 6 mean TCP on UDP on IP (as opposed to TCP on IP on UDP on IP)?

If it's the 4 in IPv4, then 6 would mean IPv6 on UDP on IPv4.

I found this bit of the article to be unclear. Looking at the patch description, I'm pretty sure it's the former. I think that the TX/RX split is a bit odd, though.

Foo over UDP

Posted Oct 2, 2014 15:47 UTC (Thu) by luto (guest, #39314) [Link] (2 responses)

And, to answer my own question for real:

On receive, the UDP header will be stripped and the payload will be processed as though it the IP sub-protocol specified in the fou configuration. If that's protocol 4 (IPIP), then the next header will be another IP header, which will be matched against an ip tunnel config.

So the RX and TX paths aren't quite as split as the article made me think.

Foo over UDP

Posted Oct 2, 2014 20:55 UTC (Thu) by jhoblitt (subscriber, #77733) [Link] (1 responses)

Why wouldn't the nested IP header have a valid protocol field?

Foo over UDP

Posted Oct 2, 2014 21:02 UTC (Thu) by luto (guest, #39314) [Link]

It does, but I think you're confused for the same reason I was.

That "4" means that this is an IPIP tunnel (so the next header is IP) as opposed to, say, a GRE tunnel with a different format.