Multi-link subnets and MIPv6 (was Re: [Mip6] Re: WG Review: Recharter of Mobility for IPv6 (mip6))

[Vijay Devarapalli <[e-mail]>]

Hi Jari and Dave,

Jari Arkko wrote:
> Hi Vijay,
>> can you send us more information on this? specifically
>> on what we are supposed to look for. document problems
>> that we might encounter when MIPv6 is run over multilink
>> subnets?

> The basic reference is the new IAB draft,
> draft-iab-multilink-subnet-issues-00.txt.

I went through this document.

first I was surprised when I saw the following
text

>    However, other WGs continued to allow for this concept even though 
>    it had been rejected in the IPv6 WG.  Mobile IPv6 [RFC3775] allows 
>    tunnels to mobile nodes to use the same subnet as a home link, with 
>    the Home Agent doing layer 3 forwarding between them. 

I was surprised to see the MIPv6 home link and the
tunnels to each mobile node being compared to a
multi-link subnet. its not a multi-link subnet as
described in draft-ietf-ipv6-multilink-subnets-00.txt.
the home agent does not bridge and forward link-scope
traffic onto the tunnels.

the draft later on says

>    A multilink subnet model SHOULD NOT be used.  IETF WG's using, or 
>    considering using, multilink subnets today should investigate moving  
>    to one of the other models.  For example, Mobile IPv6 should 
>    investigate having the Home Agent not decrement the Hop Limit, and 
>    forward multicast traffic. 

currently no link local traffic sent on the home
link is forwarded over the Mobile IP tunnel to the
mobile node.

regarding forwarding multicast traffic RFC 3775
says the following.

    Interception and tunneling of the following multicast addressed
    packets on the home network are only done if the home agent supports
    multicast group membership control messages from the mobile node as
    described in the next section.  Tunneling of multicast packets to a
    mobile node follows similar limitations to those defined above for
    unicast packets addressed to the mobile node's link-local and site-
    local addresses.  Multicast packets addressed to a multicast address
    with link-local scope [3], to which the mobile node is subscribed,
    MUST NOT be tunneled to the mobile node.  These packets SHOULD be
    silently discarded (after delivering to other local multicast
    recipients).  Multicast packets addressed to a multicast address with
    a scope larger than link-local, but smaller than global (e.g., site-
    local and organization-local [3], to which the mobile node is
    subscribed, SHOULD NOT be tunneled to the mobile node.  Multicast
    packets addressed with a global scope, to which the mobile node has
    successfully subscribed, MUST be tunneled to the mobile node.

> I would like to see documentation of how
> Mobile IPv6 is affected, and possibly, a short
> RFC that updates RFC 3775 to remove or
> reduce the problems. 

the current use of Mobile IP tunnels as an
extension of the home links does not introduce the
issues described with multi-link subnets in
draft-iab-multilink-subnet-issues. or I might be
missing something big.

comments?

Vijay

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