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Re: Implementations/suggestions for Multihoming IPv6 for DSL sites
From: Owen DeLong <owen () delong com>
Date: Mon, 11 Apr 2011 08:26:32 -0700


On Apr 11, 2011, at 8:15 AM, Luigi Iannone wrote:


On 11, Apr, 2011, at 15:37 , Owen DeLong wrote:


On Apr 11, 2011, at 6:30 AM, Luigi Iannone wrote:


On 11, Apr, 2011, at 15:17 , Owen DeLong wrote:

[snip]

Doing IPv4 LISP on any kind of scale requires significant additional prefixes which at this time doesn't seem so 
practical to me.

This is not accurate IMO. To inject prefixes in the BGP is needed only to make non-LISP sites talk to LISP sites. 
Even there you can aggressively aggregate, as explained in draft-ietf-lisp-interworking.

As long as the LISP deployment progress you can even withdraw some prefixes from the BGP infrastructure and 
advertise only a larger aggregate in order for legacy site to reach the new LISP site.

Luigi

Who said anything about BGP? I was talking about the amount of additional IP space needed vs. the
amount of IPv4 free space remaining.


Sorry. I misunderstood. 

But can you explain better? Why should LISP require more IP space than normal IPv4 deployment?

If you are a new site, you ask for an IP block. This is independent from whether or not you will use LISP.

Sure, but, if you also need locators, don't you need additional IP space to use for locators?

No, those are the IP address that you provider gives to your border router.

Right... In addition to my provider independent addresses... That's more address space than is required
if I am not using LISP.


If you are an existing site and you want to switch to LISP why you need more space? you can re-use what you have?

Perhaps I misunderstand LISP, but, I though you needed space to use for locators and space
to use for IDs if you are an independently routed multi-homed site.

Not exactly. You do not need more space. You re-use what you have. 

Still confused, then. This seems antithetical to what you said above and below...



If you are not an independently routed multi-homed site, then, don't you need a set of host IDs
to go with each of your upstream locators?

As I understand LISP, it's basically a dynamic tunneling system where you have two discrete,
but non-overlapping address spaces, one inside the tunnels and one outside.

If that's the case, then, I believe it leads to at least some amount of duplicate consumption of
IP numbers.


No true. I ask for a PI block that I will use as EID-Prefix, then the locators are part of the address space of my 
providers.
There is no duplication.


Right... Ordinarily, without LISP, I get a PI block and use that for EID and the routing is based on the
EID prefix. With LISP, the EID prefix is PI and I use additional PA resources to do the routing locators.
That's what I meant by duplication. There are additional PA resources required on top of the PI in order
to make LISP work.

Or I missed the point again?

Or perhaps the complexity of LISP in the details still confuses me, despite people's insistence
that it is not complex.


IMHO it is very simple. As any new technology  there is just a learning curve to follow, but for LISP it is not steep 
;-)

I'd agree with you if it weren't for the fact I keep thinking I just about understand LISP and then get told
that my understanding is incorrect (repeatedly).

Owen

Luigi


Owen

thanks 

Luigi



Owen






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