Subject: Re: [Mip6] GRE key

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 03 May 2007 17:43:27 +0200

Chowdhury, Kuntal wrote:
> 
>> -----Original Message----- From: Alexandru Petrescu 
>> [mailto:[email-masked]] Sent: Wednesday, May 02, 2007
>>  5:08 PM To: Chowdhury, Kuntal Cc: Alexandru Petrescu; Mohamed 
>> Khalil; [email-masked] Subject: Re: [Mip6] GRE key
>> 
>> Chowdhury, Kuntal wrote:
>>>> I think all other forms of IPv6-in-IPv4 (and in UDPv4) are 
>>>> capable to deal with the problem of overlapping private IPv4 
>>>> addressing you cite
>>> in
>>>> the draft.  Don't you think so?
>>> Alex,
>>> 
>>> If the LMA (or the HA) has overlapping IPv4 address pools, how 
>>> does it distinguish the incoming (tunneled) packets?
>> By means of mappings between addresses in the outer and inner 
>> headers. In no case by means of a new identifier (key) used as an 
>> address.
>> 
> [KC>] That is the problem. In case of overlapping IP4 HoA pools, two 
> users on the same MAG may get same IPv4 HoA, the inner and outer 
> headers will have identical information for two separate users.

How have we solved this problem in the non-mobility case?

If I have two computers, each having the same IPv4 address from
a different Enterprise, and connecting to the same Access Point, and
each having a VPN to its home - how can they talk to each other?

>>> Note that the LMA/HA needs to make this distinction for making 
>>> next hop decision. For private IPv4 addresses, that means 
>>> identifying the VLAN tag or tunnel id or the network interface on
>>>  the egress side of the LMA/HA.
>> Look, we don't even have a clear idea where _one_ NAT is placed in
> this
>> PMIPv6/v4 picture (the draft doesn't place _any_ NAT) and we 
>> speculate about two overlapping private spaces.
>> 
>> Where are the two NATs placed?
>> 
> [KC>] Let's assume that tunnels for both the users (with same IPv4 
> HoA) pass thorough the same NAT (if there is a NAT). The real issue 
> is, how to distinguish the tunnels at the LMA/HA.

I don't understand this.

You seem to assume Mobile IP is already used to give continuous access
and reachability to one IPv4 private Home Address.

> The NAT in the middle of the MAG/MN and the LMA/HA does not matter 
> since UDP transport addresses the NAT traversal problem.

But not reachability.

I'm afraid that until we have a more precise idea about where are the
NATs placed and what are the boundaries between different domains (and
the Internet) we can't say whether overlapping private address spaces is
a problem that can be dealt with by extending a protocol (the 'key') or
by using good administration.  They're exclusive.

Alex

> 
> 
>> Alex
>> 
>> 
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