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Re: [RRG] LISP question



	Robert,

> In the interest of saving time tomorrow I would like to ask for some 
> clarification reg how large corporate enterprise sites (those who run full 
> table of BGP today) would auto discover ITRs ?
>
> Their network maybe multi-as as well as multi-area. The answer from the 
> audience of LISP tutorial was that EIDs-subnets would be carried in those 
> networks in BGP to attract traffic to ITRs. But on the other hand we know 
> that there can be much more EID subnets (I think I heard 3 fold estimate) 
> then there is today IP prefixes in full BGP table ... not too mention 10^10 
> long term number.

	As you point out, today an enterprise finds its "best
	exit" by using the (BGP) routes that it learns from its
	various providers and distributing internally them with
	iBGP. If the ITRs are sitting on the edge of the site's
	network, this won't work since packets will be routed
	internally following default. A packet must follow
	default because there no information about the best exit
	for a given EID prefix.  

	So in order to preserve the behavior you are describing,
	the packet needs to be routed over the RLOC space as
	early as possible. This corresponds to placing the ITRs
	deeper in the site (closer to the source hosts). Since
	the ITR will encapsulate the packet (and the outer header
	destination address will be a locator), it will find the
	best exit just as it does today.  

> What would be the benefit and driver for such large corporate sites to 
> install ITRs ?

	Finer-grained control over exit policy without having to
	propagate global state inside your enterprise.

	Dave

	

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