Subject: [MEXT] Mobile Network Prefix forwarding

From: Vijay Devarapalli <[email-masked]>
Date: Wed, 12 Mar 2008 10:49:23 -0700

Hello,

This is the third issue.

RFC 3963 says the home agent sets up forwarding for the mobile
network prefixes when it receives a binding update from the
mobile router. If there is no binding cache entry for the mobile
router, the home agent does not have any forwarding state
associated with the mobile network prefixes.

When the mobile router boots up on a point-to-point link we have
an issue. We haven't yet standardized a mechanism for prefix
delegation, but the issue would exist irrespective of whatever
we use.

Since the mobile router is on the home link, it does not send a
BU to the home agent. But since the mobile router is only
reachable via the home agent over the p2p link, we need
forwarding entries for the mobile network prefixes on the home
agent. These forwarding entries would point to the p2p link with
the mobile router. We need to describe how the home agent sets
up these forwarding entries.

I don't have a good solution for this yet. Suggestions welcome.

If the mobile router boots up on the visited link, then there
is no issue. There is a binding update from the mobile router
to the home agent that sets up forwarding for the mobile network
prefixes. Whether we use implicit or explicit mode described in
RFC 3963 is irrelevant.

Vijay
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From: RYUJI WAKIKAWA <[email-masked]>
Date: Thu, 13 Mar 2008 04:43:08 +0900

Hi Vijay,

> associated with the mobile network prefixes.

Why does HA need the forwarding state at the home?
When MR is attached to the home link, it acts as a regular router.

The forwarding state is routing entry.
When MR boots up at the home link, it MUST operate PD for MNP.
It means HA will get indication of MN's attachment to the home link.

> up these forwarding entries.

MR can send routing update over the p2p link.
HA can create the routing entry for the MNP.

ryuji

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From: Alexandru Petrescu <[email-masked]>
Date: Wed, 12 Mar 2008 21:09:21 +0100

> This is the third issue.

Hi Vijay, this is a issue I think having seen on the slides today.

> network prefixes when it receives a binding update from the mobile 
> router. If there is no binding cache entry for the mobile router, the
>  home agent does not have any forwarding state associated with the 
> mobile network prefixes.

I'm not sure why it is said so, and I could discuss further.

However, I would like to keep in mind a perspective of the scenario and
the address architecture of where and how these point-to-point links are
used.  This is a picture I'd like to see drawn to make sure we're on the
same page.

Is the ptp link ending in the MR and in the HA?  Or is it ending into
some other entity than HA?  Is there a subnet formed between HA and the
MR when ptp link is up?

> When the mobile router boots up on a point-to-point link we have an 
> issue. We haven't yet standardized a mechanism for prefix delegation,
>  but the issue would exist irrespective of whatever we use.

MR booting up on a ptp link has nothing to do with HA having or not
having a routing table entry towards it.  I don't see what this has to
do with ptp links.

Let's think shared links.  MR booting up at home in the home link
doesn't provoke inserting routing table entries in the HA either.

The use of 'HA sets up forwarding for each of these prefixes to the MR's
CoA' is up to anyone interpretation of what 'forwarding' means.  In my
understanding that means a transparent redirection that is invisible to
routing table - the MNP-related entries in the routing table are already
there prior to HA receiving BUs.  That redirection says instead of going
to a physical interface of the HA go to an always-encapsulated-to-CoA mode.

> Since the mobile router is on the home link, it does not send a BU to
>  the home agent. But since the mobile router is only reachable via
> the home agent over the p2p link, we need forwarding entries for the 
> mobile network prefixes on the home agent. These forwarding entries 
> would point to the p2p link with the mobile router. We need to 
> describe how the home agent sets up these forwarding entries.

These should be set up prior to BU and this is true for when shared
links are used too, not necessarily ptp links.  Otherwise LFNs aren't
reachable when MR at home (neither on ptp links nor on shared links).

> I don't have a good solution for this yet. Suggestions welcome.

Static routes, dynamic protocol inserts, icmp redirects, dhcpv6 inserts
of some future implementations.  Nothing specific to ptp links, IMHO.

Trying to figure out what's specific to ptp links here...

> If the mobile router boots up on the visited link, then there is no 
> issue. There is a binding update from the mobile router to the home 
> agent that sets up forwarding for the mobile network prefixes. 
> Whether we use implicit or explicit mode described in RFC 3963 is 
> irrelevant.

Well yes, it's irrelevant and ptp vs shared links is irrelevant too in
this case.  Whether MR boots up on ptp link or on shared link the MNP
entries _have_ to be there in the HA's table prior to BU, otherwise LFNs
aren't reachable when MR at home (at home either on ptp or on shared link).

What _may_ be relevant here is whether HA is a one-interface machine on
the home link or is it _the_ router gatewaying together the MNs' ptp
links to the Internet.  And this is a matter of topology, architecture
and illustrating figures... with which we can discuss.

Alex

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From: Vijay Devarapalli <[email-masked]>
Date: Wed, 12 Mar 2008 14:23:09 -0700

> When MR is attached to the home link, it acts as a regular router.

No. The mobile router is not required to support running a
dynamic routing protocol like OSPF. The support for dynamic
routing protocols is considered optional in RFC 3963.

IMO, It is reasonable to expect a mobile router that depends
on its home agent for routing packets to it without it having
to run a routing protocol ever. We should enable this. RFC
3963 already enables that for the cases when the mobile node
is on the visited link.

> HA can create the routing entry for the MNP.

This would work, but would require the mobile router to be
able to run a routing protocol and then for the p2p link to
allow for running a routing protocol between the MR and the
HA.

Vijay

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From: Julien Laganier <[email-masked]>
Date: Thu, 27 Mar 2008 14:43:07 +0100

Hello Vijay,

<WG chair hat off>

Trying to understand better the issue. See below:

> 3963 already enables that for the cases when the mobile node

Okay. But is dynamic routing really required? Why can't the HA be simply 
set up with a static routing entry for the NEMO prefix pointing to the 
MR's address on the home link? When the MR is away that static route 
entry would be overidden by the BCE for NEMO's prefix.

> allow for running a routing protocol between the MR and the

Again, why can't we just rely on static routing entry for the NEMO's 
prefix pointing to the MR's address on the home link?

--julien

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From: "Teco Boot" <[email-masked]>
Date: Thu, 27 Mar 2008 15:53:35 +0100

> entry would be overidden by the BCE for NEMO's prefix.
[Teco:] 
There could be LFN routers or other mechanisms providing a MNP.
It makes sense both implicit and explicit modes are support.

> prefix pointing to the MR's address on the home link?
[Teco:] 
Again, there could be LFN routers or other mechanisms;-)