Subject: Re: [RAM] ViP: Anycast ITRs in the DFZ & mobile tunnels

From: "Ved Kafle" <[email-masked]>
Date: Sat, 16 Jun 2007 18:53:46 +0900

> 
> Robin,
> 
> is it correct to say that ViP anchors an access (or edge) network's
> prefix at the V-router somewhere within the DFZ?
> 
> In this case, I would see a difference between ViP and LISP 
> in terms of
> responsibilities:
> 
> - In ViP, it is the responsibility of the destination access network
>   to set up (or subscribe to) the anchor router for its prefix.
> 
> - LISP relies on a router in (or at the border of) the source access
>   network to perform this functionality.
> 
> This ViP concept reminds me of Mobile IP (v4 or v6), where a 
> mobile host
> anchors its home network prefix with a home agent, the 
> location of which
> is independent of the peer that the mobile host communicates 
> with.  Both
> ViP and Mobile IP use tunneling between the anchor and the 
> destination.
> 
> In fact, ViP is a proposal for network mobility.  It enables an access
> network to change ISPs (which is nothing else but a topological
> "movement") without losing reachability via the original prefix.

To me, the ViP approach looks similar to the network mobility (nemo) support
approach being discussed in the IETF nemo WG. In nemo, the mobile router's
home agent advertises the mobile network prefix such that the packets sent
by a correspondent node to an address belonging to the nemo prefix go to the
home network of the moible network, where the home agent tunnels them to the
current location of the mobile router. The mobile router decapsulates and
forwards the packets to the addressed node.

Analogy:
(1) ViP routers are similar to the mobile network home agents, except that
the home agents are confined to home networks where as Vip routers may be
distributed in the Internet. If we suppose that home agents can be
distributed like ViP routers, then these two apporaches are exactly the
same. 
(2) ViP's ETRs are similar to nemo mobile routers, which update ViP routers
(home agent) with the tunnel-end addresses. 
(3) In nemo, a bidirectional tunnel is set up to avoid packet filtering at
border routers. Whereas in ViP, it is assumed that the BRs forward packets
with ViP-mapped addresses. 

There are some well known problems associated with such achor point-based
approaches, such as increased packet delivery delay, non-optimal routing,
tunneling overhead, possibilities of single point of faiture, etc. To avoid
these problems, route optimization mechanisms are being investigated in the
nemo WG. Shouldn't we look for the ID-loc split solutions that avoid such
problems as much as possible?

Ved

> Interesting...
> - Christian

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From: Christian Vogt <[email-masked]>
Date: Sun, 17 Jun 2007 00:31:35 +0300

Ved:

> approach being discussed in the IETF nemo WG.  [...]

Absolutely.  This is what I was saying.

> distributed in the Internet.

Actually, ViP routers are confined in the same way as home agents in
that both can only support "home" prefixes that correspond to their
topological location in the Internet.  After all, the idea of ViP
routers is to have them advertise sub-prefixes from their ISP's global
routing prefix so that the sub-prefixes can be aggregated with the
global routing prefix and do not require a separate slot in the DFZ
routing table.

[...]

> tunneling overhead, possibilities of single point of faiture, etc. 

Right.  And things don't get better if we do the indirection for all
hosts, not just mobile hosts or hosts moving with mobile networks.

>                                                             To avoid

Without an intention to prefer either mechanism, I just want to note
that the advantage of ViP is a better transition path, whereas LISP
performs better from the perspective of packet propagation latencies and
fault tolerance.  As a matter of fact, LISP is nothing else but route
optimization (in Mobile IPv6 terms) for ViP.

- Christian

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From: Robin Whittle <[email-masked]>
Date: Sun, 17 Jun 2007 21:48:08 +1000

I will reply to Christian and Ved in the thread: "Ivip (was ViP ...)".

  - Robin