Re: New Internet Draft on automatic (end-user) tunneling for SSM

[Tom Pusateri <pusateri@juniper.net>]

In message <4.3.1.1.20010224094504.00b335f0@localhost> you write:
>At 07:26 AM 2/24/01, Tom Pusateri wrote:
>
>>If UMTP rewrites the original header plus adds the trailer,
>>it adds just the trailer which is 12 or 16 bytes.
>
>That's correct (although - wearing an "application developer's hat" - I 
>prefer not to think of it as 'rewriting the original header').  It's just 
>taking the payload from the original UDP multicast packet, adding a (12 or 
>16-byte) trailer, then resending it in a new UDP unicast packet.  People 
>who wear "router developer's hats" are welcome to think of this another way 
>if they prefer :-)

Got it. I guess I think of rewrite because a router won't forward these
at the socket level but at the IP level.

>>GRE adds: 24 bytes (20 byte IP + 4 byte GRE header)
>
>Except remember that our goal here is UDP(multicast)-over-UDP(unicast) 
>tunneling.  If you were to use GRE to encapsulate (using the term correctly 
>this time :-) a UDP multicast packet within a UDP unicast packet, then this 
>would add 32 bytes (20 byte IP + 8 byte UDP + 4 byte GRE header).

I think this is where things were confusing. There is no UDP associated
with GRE. Its pure IP just like IPIP.

>>Of all of these options, GRE or IPIP are simplest to implement in hardware
>>which will give you the performance and scaling needed for large rollouts.
>
>Right, although we also need to think about ease of deployment for end 
>users, which seems to dictate the use of a UDP-based tunneling protocol, 
>which would rule out IPIP.
>
>As for GRE (within UDP unicast): If routers can, indeed, implement this 
>significantly more efficiently than UMTP "DATA" packets, and we don't mind 
>the extra overhead (32 bytes for GRE versus 16 bytes for UMTP (or less for 
>'UMTP-light')), then I agree that we seriously consider using GRE 
>instead.  (Note, though, that UMTP 'control' packets - or something like 
>them - would still be needed in the reverse direction - to signal 'joins' 
>(plus periodic keep-alives) and 'leaves'.)

There is no point using GRE with UDP.

I forgot to include another posbbile encapsulation option which is
IP/UDP. This adds 28 bytes (20 bytes IP + 8 bytes UDP) to the front of
the packet and doesn't change the original IP datagram (header included).

This would be my preference if UDP unicast is required.

Thanks,
Tom