Subject: Re: [NSIS] LIH (was: ntlp drafts differences)

From: Bob Braden <[email-masked]>
Date: Wed, 30 Jul 2003 08:55:31 -0700 (PDT)

*> > 
  *> > Presumably you have to do that whenever you send a path message; it saves
  *> > you doing it again when you receive a Resv message. Right?
  *> 
  *>  From a practical perspective, if you send a UDP-based PATH message, you 
  *> wouldn't know which interface it left on. I think even for raw IP 
  *> packets, the kernel does the routing, without informing the sender of 
  *> the details of the interface selection decision. (Many of us would like 
  *> to implement NSIS outside the kernel...)
  *> 

Henning,

Then I don't see how NSIS can work with such a kernel.  See my earlier
message: NSIS has to be able to ask routing what decisision it will
make.

When you say "the kernel", you have to define which kernel you mean.
Cisco IOS?  Some particular flavor of Unix (different ones do it
differently).

This seems to have degenerated into a silly discussion, or else I don't
get it.

Bob

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From: Henning Schulzrinne <[email-masked]>
Date: Thu, 31 Jul 2003 11:48:38 -0400

> This seems to have degenerated into a silly discussion, or else I don't

I do agree that we're probably agreeing and talking past each other at 
the same time. Clearly, if you want to set up resources, you better know 
which interface the traffic is leaving the box on. This does not 
necessarily mean that NTLP has to know this, as long as the PATH-like 
message reaches the same next hop.

Thus, one model is that a QOS NSLP figures out (asking the routing 
table, for example) which interface is handling the packets, but NTLP 
doesn't have to.

Since not all applications will need to set interface state, not all 
applications will need to know this information, so it seems best 
handled by those who need to know.

I'm not aware of any Unix OS that propagates outgoing interface 
information to the socket; I'd definitely be curious as to whether this 
is supported somewhere. (Incoming interface information is available on 
Linux, via getsockopt IP_PKTINFO.)