Subject: [nemo] Re: Another Comment on the Nemo Basic Draft

From: Vijay Devarapalli <[email-masked]>
Date: Thu, 20 Nov 2003 11:04:54 -0800

hi Jim,

> Another possible issue with the Nemo basic draft occured to me this weekend.
> Suppose a mobile router is on its home link and there are nodes on the
> egress interface that are using the mobile router directly in order to reach
> the subnet. When the mobile router moves, these nodes will be left without
> route service for some period of time until they discover that the mobile
> router has moved.
> 
> One way to fix this problem is to have the mobile router send Redirect
> messages to any nodes in its neighbor cache, redirecting traffic from it to
> the home agent.

it will be hard for the mobile router to figure out that is moving
and then send a redirect before moving. it could lose connection to
the home link abruptly. it is also possible that at this point the
mobile router does not yet have a list of Home Agents (i.e. it
hasnt performed DHAAD yet).

but here is another suggestion. how about the Home Agent sending
a redirect for the Mobile Network Prefix when it receives a Binding
Update from the mobile router? hosts on the home link would process
the redirect and update the routes to point to the Home Agent. the
redirect is not sent if the mobile router just refreshes an existing
binding.

for the period between the Mobile Router leaving the home link and
sending a Binding Update to the Home Agent, the mobile router would
be unreachable.

this was discussed earlier in the design team. I dont remember why
we didnt add any text. :)

Vijay

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From: Vijay Devarapalli <[email-masked]>
Date: Thu, 20 Nov 2003 11:04:54 -0800

hi Jim,

Vijay

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From: "James Kempf" <[email-masked]>
Date: Thu, 20 Nov 2003 11:08:08 -0800

> we didnt add any text. :)

Rereading RFC 2461 Section 8, I now see that this isn't an issue because
Redirects only apply to the first hop router. In the scenario I described,
the mobile router is not the first hop router for a host, but rather is the
ingress router for the mobile subnet. The first hop router would be another
router on the subnet connecting the mobile router and the host, or possibly
the home agent if it is a first hop router. Thus, such a host would send
packets destined for the mobile subnet to the first hop router, which would
forward them to the mobile router.

Sorry for the confusion.

            jak

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From: "James Kempf" <[email-masked]>
Date: Thu, 20 Nov 2003 11:08:08 -0800

Sorry for the confusion.

            jak

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From: Alexandru Petrescu <[email-masked]>
Date: Thu, 20 Nov 2003 20:52:42 +0100

Vijay Devarapalli wrote:
> hi Jim,
> 
>> Another possible issue with the Nemo basic draft occured to me this
>>  weekend. Suppose a mobile router is on its home link and there are
>>  nodes on the egress interface that are using the mobile router 
>> directly in order to reach the subnet. When the mobile router 
>> moves, these nodes will be left without route service for some 
>> period of time until they discover that the mobile router has 
>> moved.
>> 
>> One way to fix this problem is to have the mobile router send 
>> Redirect messages to any nodes in its neighbor cache, redirecting 
>> traffic from it to the home agent
> 
> 
> mobile router does not yet have a list of Home Agents (i.e. it hasnt
>  performed DHAAD yet).

Yes.

> but here is another suggestion. how about the Home Agent sending a 
> redirect for the Mobile Network Prefix when it receives a Binding 
> Update from the mobile router?

Sounds good.

This is especially useful if the FN's have already been redirected by HA
in the first place towards MR (when MR was at home).

> this was discussed earlier in the design team. I dont remember why we
>  didnt add any text. :)

One issue with Redirects was that Redirects can be one of the "external"
means by which HA will learn the routes towards MR in implicit mode, if 
the HA is not GW and needs to talk to MR and MR not at home (GW will 
Redirect and HA will thus learn a route).

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 20 Nov 2003 20:52:42 +0100

Yes.

Sounds good.

Alex