Subject: RE: Next question...

From: "Tony Li" <[email-masked]>
Date: Thu, 5 Dec 2002 18:49:31 -0800

|   There is a difference between the host being aware of the routing
|   subsystem, and being aware of alternative locators. Yes the 
|   host has to
|   maintain state, but not much more than it would anyway, and 
|   the overall
|   system scales much better if state maintenance is at the edge rather
|   than somewhere in the middle.

Ok, so if the point is where to put locator selection policy, I think
that this is a much more bounded problem.  The two obvious proposals
are to

1) Put the locators in the host, so that it can control which locator
   it wants to use.  This allows the application to change locators if
   its service is unacceptable.

2) Put the locators in the border router.  This frees the host of the
   management burden, but makes it somewhat harder for a site to
   provide site-wide policy.

Note that either of these two alternatives could be enhanced by further
communications.  Either the border can inform the host of site policy,
or the host can inform the border of its local policy.  One could also
do both, but this is starting to look like a dromedary.

Does that about cover the high points?

Tony

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From: Iljitsch van Beijnum <[email-masked]>
Date: Fri, 6 Dec 2002 12:42:02 +0100 (CET)

> do both, but this is starting to look like a dromedary.

I'd go for the dromedary.

Host/router isn't the essence of the question, since if we make this for
routers it can/will be easily implemented in hosts as well. If we feel
the possibility of offloading this to an external box is unneeded it
makes sense to take advantage of end-to-end state in the host. I think
being able to offload multiaddress processing to an external box is an
important feature, since that makes it possible to multihome unmodified
hosts.  If we want to go down this road we either ignore the hosts
end-to-end state or we create (optional) mechanisms for
multiaddress-aware hosts to be more involved in this within the policy
limits set by edge devices.  This part would be complex, but as it's
optional, that isn't too huge a problem.

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From: "Tony Hain" <[email-masked]>
Date: Fri, 6 Dec 2002 10:06:05 -0800

Tony Li wrote:
> Ok, so if the point is where to put locator selection policy, 
> I think that this is a much more bounded problem.  The two 
> obvious proposals are to
> 
> Note that either of these two alternatives could be enhanced 
> by further communications.  Either the border can inform the 
> host of site policy, or the host can inform the border of its 
> local policy.  One could also do both, but this is starting 
> to look like a dromedary.
> 

Yes. 

I suspect most of the complaints about host based locator selection is
really an indirect fear of loss of control. If that is true, having the
routing system inform hosts of policy preferences would allow for that
control in the general case, but still allow individual hosts to
override it when necessary. This could be done through a local policy to
respect ordering the RA, or possibly an explicit option. 

It would be possible for the hosts to inform the routing system about
policy preferences, but the state maintenance to support N,000 policies
in current hardware would not scale. Also, how is the host supposed to
know which routers need to be informed of the policy, or if traffic
shifts during a connection, which new router needs to be updated? RSVP
tried to do exactly this, but the routing community refused to support
it over scaling concerns.

Tony

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From: Randy Bush <[email-masked]>
Date: Fri, 06 Dec 2002 10:25:39 -0800

> really an indirect fear of loss of control.

i suspect it is folk with a knowledge of just how difficult and complex
global routing is when isolated to a site border router and our minds
boggle when we think of all the hosts having to do it too.

randy

---

From: "Tony Hain" <[email-masked]>
Date: Fri, 6 Dec 2002 14:45:52 -0800

Randy Bush wrote:
> i suspect it is folk with a knowledge of just how difficult 
> and complex global routing is when isolated to a site border 
> router and our minds boggle when we think of all the hosts 
> having to do it too.

The only suggestions that hosts participate in routing are coming from
those who keep spreading FUD. 

We are talking about selection of locators, which has nothing to do with
routing. There are very simple policies here, provider A is preferred
over B, etc. It is not rocket science to configure a host to prefer one
source prefix so it will conform to traffic engineering policies in the
normal case.

Tony