Re: Elements of a DMM Solution

Hi, Marco,

Marco Liebsch wrote:
> Hi Pete,
> 
> I support your proposal. Please see (so far brief) feedback inline.
> 
>> -----Original Message-----
>> From: [email protected] [mailto:[email protected]] On Behalf Of
>> Peter McCann
>> Sent: Dienstag, 30. Juli 2013 13:09
>> To: [email protected]
>> Subject: [DMM] Elements of a DMM Solution
>> 
>> I think that the DMM work can be subdivided into a small number of
>> "modules", each of which can be implemented in a number of different
>> ways.
>> 
>> 
>> I. Limited-scope (localized) network-based mobility scheme
>> 
>> This is probably what most people have in mind when they think of a DMM
>> "protocol".  This is the mechanism that gets packets to the current
>> point of attachment.  We have seen the following proposed as options
>> for this module:
>> 
>>   A. Something based on PMIP
>>   B. Something based on GTP
>>   C. Something based on a routing protocol (e.g., BGP)
>>   D. Something based on SDN
>> We should be able to "plug in" any of the above solutions to an overall
>> DMM framework.  This module needs to be signaled when an MN attaches or
>> changes its point of attachment.  An identifier of the MN and an
>> identifier of the attachment point should be provided in this signal.
>> This module needs to interact with the address allocation/management
>> module to obtain the set of IP prefixes currently in use by the mobile
>> node, so that redirection/tunneling of packets destined to those
>> prefixes can be set up.  This may require a network- queryable database
>> of prefixes that can be indexed by mobile node identifier. This
>> database could be stored in something like an HSS or in a DNS
>> server.
> 
> Yes, or an IP mobility anchor control plane function, or a registry
> associated with an SDN controller, or.. something that can treat the
> MN's IP address (prefix) as identifier and select an appropriate
> routable locator IP address. I fully support that view that any DMM
> solution should consider hooks to external (non- mobility) protocols to
> optimize (D)MM operation and is well aligned with the methodology in our
> framework draft.

I don't think the MN's IP address (prefix) will necessarily be the identifier
of choice.  Perhaps an NAI or other identifier authenticated at the time of
access is the right one to use.

It's good to have this discussion; once we pin down the interface between
Module I and the rest of the system we can work independently on the pieces.


>> II. Address allocation/management
>> 
>> This module lives in both the MN and the network.  The MN maintains a
>> pool of addresses, each one topologically related to the point of
>> attachment at the time it was assigned.  The MN should be made aware of
>> which of its addresses are currently on-link at its current attachment
>> point, courtesy of Module I.  The MN should maintain information about
>> how it is using each address so that unused addresses can be released
>> and in-use addresses can have their leases renewed at the appropriate
>> times.  Address allocation/deallocation should NOT be coupled to node
>> mobility.  It should be possible to have a mobility event without
>> allocating a new address (to avoid excessive numbers of addresses being
>> allocated) and even if Module I cannot provide network-based relocation
>> of a prefix, mobility to an attachment point where an address is not
>> on-link SHOULD NOT trigger deallocation of the address, because the MN
>> might have a client- based mobility scheme that enables it to continue
>> using the address (Module III). Some mechanism to renew the lease on
>> the address from a remote location should be provided, such as
>> obtaining a global unicast IP address of a DHCP server.  Security
>> considerations for such remote renewal need to be investigated and
>> addressed.
> 
> So, on-link addresses are routable addresses associated with the MN's
> current anchor, whereas other addresses (off-link?) are associated
> with the previous anchor (or point of attachment) and considered deprecated.
> Correct? 

I really dislike the term "anchor".  It seems to imply there is a fixed 
point in the network through which the MN's traffic is flowing and is also
semantically linked to tunnel-based solutions.

When I say "on-link" I mean the prefix is currently advertised in an RA
on the current link (in IPv6 terms).  The degree to which it is topologically
aggregateable may vary depending on how far the MN has moved.  It may or
may not be marked as "deprecated" by the advertising AR; in any case, it 
is available for use by ongoing sessions or possibly new sessions according
to logic inside the MN.

Addresses that are not advertised on-link, if they are still needed, should
be supported with a client-based tunnel.

> Dependent on the solution for DMM, this IP address is not
> routable anymore if imported to the current anchor to enable IP
> address continuity or remains routable through the MN's previous
> anchor. In the latter case the MN may have multiple anchors which may
> have to be added to the address management module, at least in case of
> client-based mobility.

Again, don't like "anchor".  Hopefully the above explanation tells you how
I am defining my terms.

>> Module I must be provided with a list of prefixes currently allocated
>> to the MN. The database storing this information could be updated by
>> the network element that allocates the address (e.g., DHCP server) or
>> could be updated by the MN.  A network element initiated update may be
>> more appropriate for an HSS-stored database, whereas an MN-initiated
>> update may be more appropriate for a DNS- based database.
> 
> Well, in general this is about a dynamic binding in a database between
> one or more IP addresses of the MN and associated locator(s).
> Important is that this can be something else than what is provided by
> Mobile IP protocols. And this makes sense, as it applies to the
> routing space above mobility anchor level (southbound to MM U-Plane
> function, or attachment point according to your terminology).
> Who updates the database is up to a particular solution.

Again, I think the binding is from some other identifier (like NAI) to
a set of currently allocated/assigned IP addresses.  While there are 
mechanisms to allocate IP addresses using Mobile IP, I don't think they
necessarily will be used by DMM because most addresses should be 
topologically correct a the time they are assigned instead of being
routed through a home agent.

Agree that database update details are a property of individual solutions.

>> III. An optional global, client-based mobility scheme
>> 
>> Any network-based mobility scheme will necessarily have a limited
>> scope.  This is especially true in the DMM case because the Internet
>> attachment points are by definition close to the MN in the access
>> (visited) network.  Consider a roaming mobile node with home network H
>> that attaches to visited network V1. It obtains DMM service from V1,
>> obtaining an IP address topologically routed from the Internet directly
>> to V1.  Now consider this MN performing a handoff from V1 to another
>> visited network V2.  V2 has a roaming agreement with H (otherwise the
>> MN would not be able to get service) but has absolutely no business
>> arrangement with V1. Therefore, it is impossible for the network-based
>> mobility scheme to support re-routing or tunneling the packets destined
>> to the original V1 address to network V2.  We must therefore support
>> fall-back to a client-based OTT global mobility scheme, using the fact
>> that both V1 and V2 offer connectivity to the same Internet, if the MN
>> wants to keep using the address it got while connected to V1.
>> 
>> Allocation of a global mobility anchor should be coupled to allocation
>> of the address for which global mobility is needed.  There are already
>> DHCP extensions to carry HA IP addresses which could be used for this
>> purpose.  The MN-HA security association should also be bootstrapped at
>> this time, so that the establishment of security does not add latency
>> at the time the global mobility service is invoked.  We need to
>> investigate whether the current DHCP extension provides the right kind
>> of HA identifier to the MN or whether a DNS name would be more helpful
>> in bootstrapping security.
>> 
>> The global mobility anchor may invoke Module I to get the HoA-
>> addressed packets delivered to itself before tunneling them to the MN's
>> CoA. The MN should make use of Module I for its CoA in its new visited
>> network to minimize the number of global mobility location update
>> messages it needs to send to the anchor point.
>> 
>> 
>> IV. Security
>> 
>> Module I depends on a secure network access control protocol to provide
>> an authenticated MN identity.  Similarly, Module III requires
>> bootstrapping a security association between MN and HA.  So far, the
>> AAA suite of protocols have been used for this purpose.  However, it
>> may be possible to further optimize this process and unify the
>> credentials used by the various nodes if new solutions are
>> investigated.  Eliminating the round-trip to the home AAA server would
>> dramatically improve the performance of network attachment and MN- HA
>> SA establishment.  Making use of DNS-based public key credentials that
>> can be locally cached may allow the elimination of this round-trip and
>> improve the scalability of home network infrastructure.
>> 
>> These enhancements to security can be decoupled from the rest of the
>> architecture and investigated separately.
>> 
>> 
>> 
>> 
>> I think it's important for the DMM working group to investigate all 4
>> of the above solution components, even though most people in the group
>> are probably focused on Module I for now.  We need to understand how
>> the pieces will fit together into an overall system. To the extent we
>> need to make changes to MN implementation practices, we should publish
>> advice in Informational RFCs. To the extent we need to modify protocols
>> that are outside the scope of DMM, we should send requirements to other
>> working groups and encourage the work to get done.
> 
> 
> Makes sense to me.

Ok, good.  Maybe if we can get agreement on the various pieces we can
arrive at an updated framework document.

-Pete

> 
> marco
> 
>> 
>> 
>> --
>> Peter J. McCann
>> Huawei Technologies (USA)
>> [email protected]
>> +1 908 541 3563
>> Rm. C-0105, 400 Crossings Blvd. (2nd floor), Bridgewater, NJ
>> 08807-2863  USA
>> 
>> 
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