Subject: RE: Call for Comments on Issues ID

From: Charles Perkins <[email-masked]>
Date: Thu, 5 Mar 1998 16:45:12 -0800 (PST)

Erik, Chip,

> > More seriously, have we considered exactly how IP addresses
> > are expected to work in an ad-hoc network? Maybe we have,
> > and I'm just forgetting....
> > 
> > -- Chip
> 
> Unique numbering, which is used for addressing MANET hosts,
> seems to be critical to all the proposals.  When I have asked
> in the past, during WG meetings, where these numbers come
> from, the answer has been 'they are just there' - perhaps from
> a MAC address.  It seems like prenumbering is a requirement for 
> any MANET protocol.  Or would dynamic host configuration make 
> sense in an ad hoc protocol (MADHCP? Stateless MAADDRCONF?)

MADDRCONF or MADHCP have the appropriate first three initials.

If the addresses are assigned to facilitate renumbering, then
movement will require address reassignment.  That's MAD.

If the addresses are assigned randomly, then it might be very
hard to perform duplicate detection (DAD in ND).

If the addresses depend on the MAC address, then things are better
(assuming life in MAC World is better), and that's fine.

Let's just say the addresses are predefined.

Regards,
Charlie P.

---

From: Chip Elliott <[email-masked]>
Date: Thu, 05 Mar 1998 23:28:39 -0500

>Let's just say the addresses are predefined.

Charlie,

As usual, I cannot tell if I'm being a blockhead or not.
(And please do not ask my co-workers.)

Let me ask my question in very slow motion. Then someone
can correct my mistaken thoughts. Note that this question
is distinct from Erik's good question about node ID's.

1. Do we expect the radio interface on a computer
   (host/router) to have an IP address?

2. If so, isn't it true that this IP address is of the
   form [network,host], with a mask that shows the
   dividing line between these two portions?

3. Isn't it true that all the computers on this radio
   network must have the same network part, ie,
   agree on [network,*] and mask?

4. Isn't it true that all the computers on this radio
   network must have distinct host numbers, ie, each
   have a unique value for [*,host]?

I *think* all these things are true, but maybe some of
us don't believe some of these points. (Eg, maybe the
radio interfaces don't have IP addresses; but then
how could we communicate with a machine that only had
a radio interface. Eg, maybe the radio looks like a
bunch of point-to-point links. Eg, maybe agreement is
not required, and everyone can use any [network,host]
pair that they like.)

Come on guys, help me out here!

Now, we have sometimes also stated that one goal of
MANET was to have a bunch of people plunk down their
laptops on a big table, and have a network form
automatically.

5. Do all these people have to manually configure the
radio IP addresses so this will work?

6. Or is there some "missing piece" protocol that does
this for them, ie, a MADARP or MADHCP equivalent?

7. Or was this not really a goal, just a pleasant thought?

I know I'm beating a fairly dead horse, but I really
do not understand if this group has a common opinion
(and I'm the only one in the dark), or whether we all
think manual configuration is the right answer, or we
all acknowledge that there's a missing piece but consider
it outside the scope of this group, or what.

All help will be appreciated.

Cheers,

-- Chip

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From: "Vincent D. Park" <[email-masked]>
Date: Fri, 06 Mar 1998 10:02:53 -0500

Chip,

Thanks for bringing up this subject. I think that this is a topic that has
likely been discussed at length within small groups (i.e., two to three
individuals), but I don't think it has been sufficiently discussed in the
working group as a whole. I think this is potentially a big can of worms,
but it should be discussed. Some of my thoughts are below.

Unfortunately, I think that methods for addressing and subnet masking are
somewhat tied to the architecture (i.e., isolated -vs- connected to
Internet, single routing domain -vs- multiple routing domains, etc.) and
the desired functionality (i.e., are new host/routers allowed to
arbitrarily join a routing domain?, do we assume any such newcomers have a
preassigned address?, etc.). My answers below reflect the current direction
for the TORA and IMEP drafts. In a sense, a *near term goal* for a mobile
routing solution that is compatible with current IP practices and could be
used for routing within an autonomous system that may or may not be
connected to the Internet.

>   (host/router) to have an IP address?

Yes! As you know, in IMEP we are actually considering the case where a
host/router may have multiple wireless and/or hardwired interfaces. As with
current practice, each interface would have a separate IP address and
subnet mask.
>   dividing line between these two portions?

Yes. For any hardwired interfaces nothing is different (i.e., addresses can
be aggregated using the subnet mask). Thus, the mobile routing domain can
include "subnet routes" (e.g., a subnet route to an ethernet on a moving
platform). For the wireless interfaces, I think the ability to aggregate
*within* the routing domain is lost. Thus, within the routing domain, a
route to a wireless interface of a host/router would essentially be "host
route" (i.e., 32 bit subnet mask).
>   agree on [network,*] and mask?

A don't think this is necessary; however, for an autonomous system
connected to the Internet (or even just another routing domain) this may be
advantageous. The idea here is that routes advertised outside of the mobile
routing domain can aggregated using a subnet mask.
>   have a unique value for [*,host]?

I think all that is required here is the same level of uniqueness required
under current IP practices. For example, an isolated system need only
ensure that IP addresses are unique within that system. 

One last thought about host/routers arbitrarily joining an autonomous
system or routing domain. If the system is isolated (i.e., a subnet mask is
not being used to aggregate addresses for advertising externally) then as
long as host/routers are using globally unique IP addresses, a host/router
should be able to join and use its current address. If the system is
connected to the Internet or another routing domain, then this sounds like
a "mobile host" type problem. This not part of the *near term goal* being
addressed by TORA and IMEP.

Let me know if I'm talking in riddles or babbling nonsense ;^)

-Vince

+---------------------------------+
| Vincent D. Park                 |
| Information Technology Division |
| Naval Research Laboratory       |
| 4555 Overlook Ave.              |
| Washington, DC 20375-5000       |
+---------------------------------+

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From: "M. Scott Corson" <[email-masked]>
Date: Fri, 6 Mar 1998 15:04:35 -0500 (EST)

> current practice, each interface would have a separate IP address and

This is a rather crucial point. The real reason for using IP-level
routing in a MANET is to provide network-level consistency and integrity
for multihop networks consisting of devices using a *mixture* of physical-layer
media...in other words, a mixture of what are commonly thought of as
subnet technologies.  A MANET node principally consists of a router, which 
may be physically attached to multiple IP hosts (or IP-addressable devices),
which has potentially *multiple* wireless interfaces--each interface using
a *different* wireless technology.  Thus, a MANET node with interfaces
using technologies A and B can communicate with any other MANET node
possessing an interface with technology A or B.  The multihop connectivity of 
technology A forms a physical-layer multihop topology, the multihop 
connectivity of technology B forms *another* physical-layer topology
(which may differ from that of A's topology), and the *union* of these
topologies forms another topology (in graph theoretic terms...a multigraph),
termed the "IP routing fabric", of the MANET.  MANET nodes making 
routing decisions using the IP fabric can intercommunicate using either
or both physical-layer topologies simultaneously.  As new physical-layer
technologies are developed, new device drivers can be written and
another physical-layer multihop topology can be seamlessly added to
the IP fabric.  Likewise, older technologies can easily be dropped.
Such is the functionality and architectural flexibility that IP-layer
routing can support, which brings with it hardware economies of scale.  
If one only has a single physical-layer technology,
why not use, for example, HIPERLAN as a subnet and speak IP at the edges?

Future networks will almost assuredly employ multiple physical-layer 
technologies simultaneously.  The military has the requirement *now*.
Ships, tanks, planes, etc. using multiple technologies.  Future smaller
devices will likely be multimode (in terms of communications technologies).  
Glueing them together at the IP layer makes sense.

I think Charlie is correct in that using IP-layer MANET routing sort of 
breaks the subnet model.  It does in a way.  In fact, a MANET node
(a router physically attached to a group of hosts) resembles a *mobile* subnet.
The multihop topology of the MANET fabric interconnects these
"mobile subnets".

The concept of the "router ID" as put forth in IMEP is crucial to supporting
the multigraph topology of the routing fabric.  It is what *unifies* a
set of wireless IP interfaces on the same mobile platform.
Router IDs are used at the IP layer for routing computations.
To enable IP routing to hosts associated with the router, 
the subnet mask(s) (encompassing the hosts on the mobile platform)
should be advertised with the router ID to permit routing
table construction.

The methods for assigning router IDs needs thought, both near term and
far term.  Right now it's unspecified.

-Scott

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M. Scott Corson                                 Institute for Systems Research
[email-masked]                              A.V. Williams Bldg. (115)
Phone: 301-405-6630 (Rm. 2205 AVW)              University of Maryland     
Fax:   301-314-8586                             College Park, MD  20742

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