Subject: Re: Identifier/locator recap

From: "J. Noel Chiappa" <[email-masked]>
Date: Tue, 18 Mar 2003 11:37:26 -0500

> From: Iljitsch van Beijnum <[email-masked]>

I've been meaning to send in a minor rant for some time now, and this message
gives me a good hook..

    > Traditional multihoming as is done in IPv4 will not scale.

That is to say, multihoming which is supported entirely by the routing.

    > An alternative is to give each host in a multihomed site an address for
    > each ISP the site is connected to. .. However, current transport
    > protocols are unable to jump to new addresses in mid-session. Solution:
    > separate the identifier and locator functions of the IP address.

Here's my rant:

This group is spending a lot of its time discussing the identity/location
separation. I wish to make it crystal clear that this is a *secondary* issue
when it comes to supporting multi-homing (the expressed purpose of this
group :-).

The way in which one does multi-homing that scales is use of multiple
routing-names (a.k.a. addresses)#. Not as much attention has been given to
this part of the problem (e.g. how do you decide which address to use, how do
you decide when to switch, etc) although I have recently seen some traffic
about it.

But please everyone, keep in mind that separation of location and identity is
*not* what supports multi-homing - what makes multi-homing work is use of
multiple addresses. Separation of location and identity comes in because of
*other* concerns that people have.

	Noel

Note #: I think it's possible to do multi-homing with only a single
routing-name (a.k.a. address) - but to do so would require that the addresses
be asigned automatically by a system which was looking at the actual physical
connectivity. In other words, addresses would not be assigned by a registry,
and would change as the topology changed. In terms of the location/identity
issue, you'd still wind up with the same problem, that an address was not a
useful long-term idenitifer of *who* you were talking to - it would only say
*where* it is.

---

From: marcelo bagnulo <[email-masked]>
Date: 18 Mar 2003 18:09:24 +0100

Hi Noel,

Fully agree with your comment, just wanted to add...

> multiple addresses.

...bound to *one* (upper layer) identifier (which can be both a locator
and an identifier (like HoAs)). 

IMHO this is the difficult part (security, preservation of established
connections)

>  Separation of location and identity comes in because of
This is solution for a more general problem but it also addresses this
particular issue. If the identifier and the locator are already
separated and the architecture provides tools to bind them safely, i
would say that you have solved the mh problem. 

Regards, marcelo

-- 
marcelo bagnulo <[email-masked]>
uc3m

---

From: Masataka Ohta <[email-masked]>
Date: Wed, 19 Mar 2003 02:43:46 +0859 ()

Noel;

> *not* what supports multi-homing - what makes multi-homing work is use of

Supporting multiple addresses becomes extremely simple with ID/locator
separation, extremely complex otherwise.

> *other* concerns that people have.

Simplicity of specifications and implementations, which are essential
requirement to have multihoming or anything else.

> and would change as the topology changed.

You are saying to use multiple addresses as the topology change.

You also ignore that if a topology allows for multiple pathes
between hosts, there can be multiple addresses of a host.

And, it is a scalability problem for a registry to reassign addresses
upon topology change to all the affected hosts.

							Masataka Ohta