Subject: RE: concerns about tunnels

From: "Don Fedyk" <[email-masked]>
Date: Mon, 27 Sep 2004 13:25:14 -0400

Mike and Stewart

We can break an IP in IP tunnel to components:

1) The encapsulation header
2) The tunnel integrity maintenance: sequencing, fragmentation etc
3) The Adjacency, or topological state (some way to know the two end points
are alive)

You seem replied to me all you really need is 1).

What Alia and I have been saying is although you somehow virtualize 2) and
3) and only put 1) in the FIB and claim stateless we have our doubts it is
as simple as that. 

Just because you don't create a tunnel with end to end signaling does not
mean that you can escape checking the validity of  the end points.  

Just because you don't do a CSPF path and signal it doesn't mean you don't
have to produce a Next hop that is "constrained" to be a valid as an
alternate next hop and a reasonable path variation. 

Simply avoiding point to point signaling and relying on Routing updates and
topology calculations does not remove the constraints and state, it only
moves them to another place.  Don't get me wrong I think removing point to
point signaling has some merit but we must represent the tradeoffs in a
balanced view. 

Regards,
Don 

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From: mike shand <[email-masked]>
Date: Mon, 27 Sep 2004 19:43:46 +0100

At 13:25 27/09/2004 -0400, Don Fedyk wrote:

Mike and Stewart

2) The tunnel integrity maintenance: sequencing,
fragmentation etc

3) The Adjacency, or topological state (some way to know the
two end points are alive)

What Alia and I have been saying is although you somehow virtualize 2) and 3) and only put 1) in the FIB and claim stateless we have our doubts it is as simple as that.

Just because you don't create a tunnel with end to end signaling does not mean that you can escape checking the validity of  the end points.

Just because you don't do a CSPF path and signal it doesn't mean you don't have to produce a Next hop that is "constrained" to be a valid as an alternate next hop and a reasonable path variation.

Simply avoiding point to point signaling and relying on Routing updates and topology calculations does not remove the constraints and state, it only moves them to another place.  Don't get me wrong I think removing point to point signaling has some merit but we must represent the tradeoffs in a balanced view.

Yes, I see what you mean. In some sense the tunnel set up is there, but the actual setup is only a local matter. The only information you need to exchange (and you can do this in the IGP) is the fact that the router is prepared to be a tunnel endpoint, and what the information required for directed forwarding to each of the neighbors is. Everything else is then done by the router computing the repair path, and the alternate FIB is simply set up with the required information for use if and when needed.

Mike

Regards,

Don