Subject: [mobile-ip] comments on draft-kempf-mobileip-arch-00.txt

From: "Hesham Soliman (EAB)" <[email-masked]>
Date: Tue, 4 Mar 2003 10:44:44 +0100

cc'ing the charter list because this draft is making 
recomendations based on the rationale presented. 

I have intentionally avoided addressing any of the WG split
discussions in my comments because I'd like to understand
this draft first. 

Also there is no editorial comments.

Comments:

Abstract
   "A natural architectural split exists in Mobile IP between the 
   mechanisms involved in global routing change and the mechanisms 
   involved in local link routing change"

Mobile IP does not handle routing changes. Routing protocols
do that. MIP handles host movement. So I think that 
this description is not accurate.

What is "Global routing change"? and what is "local routing change"?

   "The global mechanisms modify 
   the mapping between a Mobile Node's routing identifier (care of 
   address) and its global node identifier (home address)"

Perhaps "routing identifier" can be replace by "locator". 

   "The local 
   mechanisms allow the Mobile Node to obtain IP connectivity on the 
   subnet and provide measures to locally mitigate routing failure 
   while the global routing change is occurring"

"Local mechanisms" do not alow the MN to obtain IP connectivity.
I think ND does that. 

Where is the "routing failure"? Routing does not fail, it
still works and packets are delivered to other nodes. 
What happens is that the MN moves. Perhaps you could
say that there is a loss of connectivity, link failure ..etc
but there is no routing failure here. 

Section 1.
----------

     "A change in the global routability of packets due to movement 
     betweens subnets"

"Global routability" ? I don't understand this term.

Section 2
---------

   "The Internet routing architecture uses an IP 
   address for two purposes: 
    
   - To provide a globally unique node identifier for use by the 
     transport layer, which is the node identifier, "

Actually, Internet routing does not use IP addresses for
this purpose. MIP does though for reachability and 
transparency to upper layers.

   "In addition, packets 
   from the Mobile Node are typically also reverse tunneled through the 
   Home Agent, if ingress filtering in the access network is operating."

Reverse tunnelling is (at least for v6) independent of 
the presence of ingress filtering. It will always happen.

Section 3
---------

   "3.0   The Local Routing Problem "

I don't see any "routing" problem. The MN moves, 
that is not a routing problem. To avoid repeating myself
please regard this as a general comment on the draft. 

  "The local routing problem consists of two parts: 

  1) The need for a mechanism by which the Mobile Node obtains a new 
     care of address on a new link,  
  2) The need for a mechanism to temporarily repair the local routing 
     failure due to a switch in link prior to the change in global 
     routing at the Home Agent (and, in route optimized, Mobile IPv6 
     Correspondent Nodes) taking place. "

(1) is already addressed in ND in v6. 

   "In many 
   respects, the Foreign Agent looks like an on-link Home Agent. It 
   maintains a binding between the care of address (typically the 
   global address of the Foreign Agent itself) and the link layer 
   address of the Mobile Node, similar to the binding cache maintained 
   by the Home Agent."

I don't think this is correct. 

   "At the extreme, a regional routing proxy may be required 
   for every subnet, like a Foreign Agent, or for every aggregation 
   router serving a collection of subnets through a low capacity edge 
   link, like a T1 line. "

Why "low capacity edge link like a T1 line"? This seems
to be influenced by a low bandwidth access network scenario. 
It could also be a high speed link like 100Mbps Ethernet.

   "Because both the mechanism and expected deployment pattern of the 
   regional routing proxy involve mechanisms more similar to the global 
   Mobile IP architectural elements, "localized" mobility management 
   should more properly be called "regionalized" mobility management, 
   and therefore regional routing proxies are more properly considered 
   part of the global, not local, Mobile IP architecture. "

Naming conventions aside, I think the rationale of this
paragraph is a bit weak. So because the agents are
"regional" (which is a name the draft proposes) and
because they "act like HAs", they should be considered
part of the "global problem" ?? Shouldn't this 
classification be made based on the problem that they
solve rather than _how_ they solve it? 

I have a few more comments and will send them later.
This email is becoming too long.

Hesham

---

From: "James Kempf" <[email-masked]>
Date: Tue, 4 Mar 2003 11:26:26 -0800

Hesham,

Thanx for the comment. Some responses to your comments.

> this description is not accurate.

My copy of Webster's New Collegiate Dictionary (1979, i.e preInternet) defines
"routing" somewhat circularly:

     routing: to send by a selected route, to divert in a specified direction

and for a route (in this context):

    route: a traveled way, a line of travel, an established or selected course
of travel or action

To the extent that a home agent diverts packets in a specified direction toward
a mobile node, it is performing routing. To the extent that a binding update
causes that specified direction to change, there is a routing change.

> What is "Global routing change"? and what is "local routing change"?

Defined in the text, but perhaps we need to call this out more clearly in the
next draft.

> Perhaps "routing identifier" can be replace by "locator".

OK.

> "Local mechanisms" do not alow the MN to obtain IP connectivity.

Right, that's exactly the point. ND is one of the mechanisms that allow the MN
to deal with mitigating the routing failure. FIMP is another.

> but there is no routing failure here.

My Webster's defines failure as:

    failure: a falling short

To the extent that the packets directed to the MN fall short of the MN (by
virtue of their getting dropped at the old AR) when the MN moves, there is a
failure, until the binding update occurs.

> Section 1.

Websters on global:

    global: of, related to, or involving the entire world

Routablity is derived from the above, namely the capability to be sent in a
particular direction. Thus global routability implies capability of directing
across the entire world. Considering the Internet's current span, I think this
is accurate.

> transparency to upper layers.

The TCP (and now SCTP) uses the IP address to identify an outstanding connection
to a node. Perhaps we should have qualified this as "the Internet architecture"
rather than "routing architecture" because it involves the Transport Layer which
is not directly involved in routing.

> the presence of ingress filtering. It will always happen.

OK. The draft spans v4 and v6.

> please regard this as a general comment on the draft.

See above. The movement causes the routing problem.

> (1) is already addressed in ND in v6.

The draft is discussing architectural considerations, not specific mechanisms.

> I don't think this is correct.

Uh, why?

> It could also be a high speed link like 100Mbps Ethernet.

OK, we can drop this. This is an implementation consideration independent of the
architeture question. It was meant to be an example.

> solve rather than _how_ they solve it?

I agree that regional mobility management may be in a separate category. This
issue came up in other email, next version will break this out.

            jak

---

From: "Xiaoming Wang" <[email-masked]>
Date: Wed, 5 Mar 2003 11:01:54 +0900

Hi, James, I'd like to cut in the discussion to present my opinion. Please
correct if I'm misunderstanding.

> causes that specified direction to change, there is a routing change.
I think it's better to achieve consensus on the definition of "routing". In
the field of network protocol, it's more proper according to technical
conventions to interpret "routing" as "IP routing", which specifically
regards routing in IP layer. The definition from Webster, which you refered
above, is a general one and can not be used in the draft without explicit
notation. So if you prefer this word to continue to appear in the next
version of the draft, could you please give explicit notation first, which
will assist better understanding?

For me, MIP is consumer of IP (correct me if I'm wrong). MIP is built upon
IP layer, similar to ICMP, which serves as accessorial component and
provides additional function for IP. From this viewpoint, MIP doesn't
involve in IP routing. In steady it utilizes routing function of IP to
perform Binding Update and packet forwarding.

> Defined in the text, but perhaps we need to call this out more

I agree. Moreover, I'd like to see more clear criteria of delimiting these
two parts. Here I would present my understanding. First of all, I suggest to
replace "routing" with "location" in these two phrases. IMHO, it seems more
understandable. Here I use *** to denote the word of "routing" or
"location". From the draft, "global *** change" can be understand as a
global view of mobility, which focuses on the global effect of changing CoA
and whose core issue is maintainence of mapping between HoA and CoA, while
"local *** change can be understand as a local view of mobility, which
focuses on the local effect of MN's moving between ARs and whose core issue
is to maintain connectivity during this period, which cannot be covered by
MIP perfectly.

> issue came up in other email, next version will break this out.

I think the draft needs a better rationale for catergorization. A fuzzy one
cannot be understood and accepted.

MIP working group will be divided into two working groups: one for MIPv4 and
another for MIPv6. The motivation is from vast difference in these two
parts. So is it good to contain related contents for both of MIPv4 and
MIPv6? IMO, the contents for MIPv4 and for MIPv6 are also very different
from each other, which inherite from the relationship between MIPv4 and
MIPv6. What do you think about it?

Anyway, thanks for your work. It helps me to achieve better understanding of
the current messy world. More work is needed on the draft before it becomes
more valuable.

xiaoming

---

From: "James Kempf" <[email-masked]>
Date: Wed, 5 Mar 2003 11:30:18 -0800

Xiaoming,

The point I was trying to make is that routing involves getting packets from
here to there. To the extent that the home agent is doing that, Mobile IP is
involved in routing. To the extent the the MIP protocol provides for messages
that allow an MN to change where its packets are going, routing change is
involved.

            jak

----- Original Message -----
From: "Xiaoming Wang" <[email-masked]>
To: "James Kempf" <[email-masked]>; "Hesham Soliman (EAB)"
<[email-masked]>; <[email-masked]>
Cc: <[email-masked]>
Sent: Tuesday, March 04, 2003 6:01 PM
Subject: RE: [mipcharter] comments on draft-kempf-mobileip-arch-00.txt