Re: [RRG] some musings on PI v. PA, and assumptions, requirements, and tradeoffs

[jnc@mercury.lcs.mit.edu (Noel Chiappa)]

    > From: marcelo bagnulo braun <marcelo@it.uc3m.es>

    > if we want to restore such functionlity without burdening the routing
    > system we will need additional mechanisms that will have a cost.

I'm (obviously :-) mostly in general agreement with this point, but I'm a
little puzzled by the term "restore .. functionality". I'm not sure exactly
what "functionality" you're referring to, but... I always thought of
multi-homing as something new, something extra, which we were doing; creating
more reliability. So, to me, anything that doesn't work is not something that
used to work, but doesn't any more...


    > a similar considration can be applied to the TE discussion and using PA
    > addresses. I mean, when we only use PA addresses and the only one that
    > knows that 2 PA prefixes are assigned to a single site is the site
    > itself, then the rest of the network cannot perform TE tricks. This is
    > a similar trade off: the rest of the network is no longer overloaded
    > with additional routing information, but as they no longer have the
    > information about all the paths leading to a multihomed site, they can
    > not longer play with different paths.

Excellent point.

    > If we want to restore such functionality, we will need to pay to
    > publish that information, either by bigger routing tables, either
    > having a parallel database that contains the multiple PA prefixes
    > assigned to each multihomed site

Two comments.

First, you're right: from a high level, providing these extra services (TE,
in this case) is going to require extra overhead/etc (TANSTAAFL).

Second, at a certain point, I think the existing routing architecture (since
these are all path-selection issues, i.e. routing) is going to prove too big
a problem. At a certain point, you wind up trying to install screws with
a hammer...

	Noel

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