Subject: [Autoconf] comments on draft-ietf-autoconf-manetarch-07.txt

From: Thomas Narten <[email-masked]>
Date: Tue, 04 Dec 2007 08:43:58 -0500

2007-11-30 review of -7

Overall. I still do not think this document is ready for
publication. It is still to vague/muddy on the key architectural
points  that it is supposed to explain.

My major concern is that you still do not lay out an understandable
"architecture" that allows one to understand what an IP subnet would
look like in MANETs.

Interface terminology is non-standard and confusing. Should use "link
type". Really. If you want the rest of the community to be able to
understand this stuff, you cannot redefine terminology that is already
widely in use and understood to mean something different than who it
is used in this document.

   Neighbor
      In the context of routing, two routers are neighbors if one can
      send/receive routing protocol IP packets to the other without
      passing through any intermediaries at the same layer.

Why "router"? Definition of neighbor from from 2460 should be used
instead:

   neighbors   - nodes attached to the same link.

Why (or why isn't) the RFC2460 definition sufficient?

   Interface
      A node's point of attachment to a communication link.

This is mostly fine as written, but...

   Semi-Broadcast Interface (SBI)
      A broadcast capable interface that may exhibit asymmetric
      reachability.  Multiple access wireless radio interfaces are often
      SBI.  Note that since a SBI *may* exhibit asymmetric reachability,
      it also may not.

Call it a "link" not an "interface".

Manets provide IP with a conceptual link, that has certain
properties. What I thought the MANET architecture would provide is a
description of the properties of that link type.

   MANET Interface
      A MANET interface is distinguished by its potentially significant
      time-varying asymmetric reachability (e.g., SBI) amongst potential
      neighboring routers.  A more detailed discussion of MANET
      interface characteristics is presented in Section 4.2.  The
      addressing constraints for a MANET interface are discussed in
      Section 5.2.

No. A MANET _link_ has these characteristics. Not the interface.

Etc.

   MANET Router (MNR)
      A MANET router is distinguished by having one or more MANET
      interfaces.  A MANET router may also have zero or more non-MANET
      interfaces.  A MANET router is responsible for hiding MANETs'
      challenging characteristics from nodes that are not MANET-aware.
      A MANET router with a single MANET interface is illustrated in
      Figure 1.

No. the "interface/link" hides the challenging characteristics from
IP. Not the BR itself. This is a critical point (architecturally) to
get right.

You really (I think) need to define an abstraction that defines an
link type of "manet" that handles all the "interesting"
characteristics of MANETs (like non-transitive connectivity) but that
also presents itself to IP as a single IP subnet that has the normal
properties.

   MANET Neighborhood
      a set of neighboring routers that can communicate via MANET
      interfaces without passing through any other routers
      (intermediaries at the same layer).

If A can reach B, B can reach C, but A cannot reach C, are A&C in the
same neighborhood? from the wording, I think the answer is no, per the
definition of "neighbor". Do I understand that correctly? 

   MANET
      a routing domain containing MANET routers.  A example MANET is
      illustrated in Figure 3.

This is too vague (i.e, it's a meangless definition). If I have two
manet routers connected to each other, plus 100 ethernet links
connected by routers, is the entire set considered to be part the
"MANET"?

   receive the packet from PR1 on its interface and determine that it
   must retransmit the packet over the same interface as the one where
   the packet was received, in order for the packet to reach PR3.  From

s/retransmit/forward/

   Wireless interfaces often exhibit more challenging characteristics
   when compared to wired interfaces.  Many protocols (e.g., IPv6
   neighbor discovery [RFC4861]) were not designed to operate in
   wireless networks with asymmetric reachability.  Wireless interfaces
   may also exhibit very dynamic time varying performance (e.g., packet
   loss, data rate), and the factors have a significant impact on local
   communication.

Be more precise. ND assumes  a standard IP subnet model that all nodes
on the same subnet are neighbors.

Also, it is wrong to say "wireless vs. wired". What you really mean is
that the link characteristics of things like typical ethernet differ
from the link characteristics of other technologies.

The challenge for MANETs is to figure out how to work around that
assumption.

   Ad hoc networking further compounds problems by allowing nodes to
   join and leave the network, or even form new networks, at will.

Do you mean "links"? or "subnets"? Saying "network" is vague.

4.2.  Challenges

   MANET characteristics result in many challenges.  These challenges
   reveal themselves in many forms, and MANET specific protocols must
   often be developed.

I don't like this wording. what is unclear here is _what_ protocols
will need to do this, and to what degree these are MANET-specific
(hidden under an abstraction of an interface looking like a normal IP
subnet, with emulation underneath to deal with the manet challenges)
or something else.

   In MANETs' with SBI, MANET routers within the same small geographic
   region are often densely connected with other nearby MANET routers.
   These routers form a set of extended neighbor relationships.  This
   set is referred to as a MANET neighborhood.  A MANET neighborhood is
   typically composed of several MANET routers, with each MANET router
   being densely connected to other MANET routers.

Shouldn't this be in the defintion section?

   logical.  For example, in an Ethernet network nodes are often told
   that a particular range of addresses are "on-link".  In MANETs' a
   MANET router often cannot make assumptions that a particular set of
   MANET routers is always (directly) reachable.  Instead, MANET routers
   must detect and determine neighboring MANET routers, and handle
   changes to this set over time.

Again, I find the term "MR" vague here. The issues here have to do
with MANET-specific things, and refer only to the MANET links. Yet,
the MR definition is broader, and simply says "a router with at least
one interface to a MANET".

I would expect section 5.2 to clarify what the basic MANET subnet
model is. But it does not.

   Unique Prefixes
      MANET interfaces that are known to exhibit the above mentioned
      properties must be configured with unique prefixes.  The reason
      for this requirements is so that no two MANET interfaces are
      configured to appear within the same IP prefix.  One way to
      achieve this is /128 (IPv6) or /32 (IPv4) prefixes.  It is worth
      noting that prefix lengths shorter than /128 (IPv6) or /32 (IPv4)
      are possible on the MANET interfaces, as long as the prefixes are
      unique to a single MANET interface.  Note that the above
      statements are not an exception, but simply a clarification that
      MANET are no different from other networks in this respect.

Don't understand this. More specifically:

      MANET interfaces that are known to exhibit the above mentioned
      properties must be configured with unique prefixes.  The reason
      for this requirements is so that no two MANET interfaces are
      configured to appear within the same IP prefix.

Why? Is this a requirement specific to MANETs, or is this a more
general requirement?

      One way to
      achieve this is /128 (IPv6) or /32 (IPv4) prefixes.  It is worth
      noting that prefix lengths shorter than /128 (IPv6) or /32
      (IPv4)

Sorry, but a /128 or /32 is an address, not a prefix (practically
speaking). If you really mean "an address", why don't you say so. 
      
      are possible on the MANET interfaces, as long as the prefixes are
      unique to a single MANET interface.  Note that the above
      statements are not an exception, but simply a clarification that
      MANET are no different from other networks in this respect.

If this is really a standard requirement of IP, I still don't get what
issue you are trying to raise or why you are point this out.      

Link-local Multicast/Broadcast Scope
      On a MANET interface, a packet sent to a link-local multicast or
      all-ones broadcast address reaches the MANET interfaces of
      neighboring MANET routers, regardless of their configured
      addresses.  Link-local multicast/broadcast packets are never
      forwarded and since a MANET may span several hops, nodes cannot
      assume that a packet sent to a link-local multicast/broadcast
      address will reach all routers within a MANET.

Sorry, this is bogus. "link-local multicast" is defined by IP and
means that a packet sent to that address is delivered to all nodes on
the "link". This latter part, that says "never forwarded" does not
make sense.  They are never forwarded beyond the link, but they may be
forwarded by MRs (your terminology) if required by the "link
model". You cannot just say that multicast doesn't work in MANETS, and
then imply protocols at the IP  layer need to take that into
account. That would be changing the basic IP model.

Thomas

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---

From: "Teco Boot" <[email-masked]>
Date: Tue, 4 Dec 2007 17:55:04 +0100

Some comments inline.

> -----Oorspronkelijk bericht-----
> Van: Thomas Narten [mailto:[email-masked]]
> Verzonden: dinsdag 4 december 2007 14:44
> Aan: [email-masked]
> Onderwerp: [Autoconf] comments on draft-ietf-autoconf-manetarch-07.txt
> 
> 2007-11-30 review of -7
> 

Maybe better definition could help.
I think it is easy to understand that a MANET Interface is an interface that
may suffer from certain link characteristics. We have similar kind of
interface types, like NBMA and P2MP. Now we want to define another.
Term MANET Interface is well known, e.g. it is used in MANET Routing
Protocol documents, including the OSPF ones.

Maybe term Semi-Broadcast Interface (SBI) should be removed, this is about
the link characteristics. Hint for editer: Change SBI into MANET and some
textual cleanup will do.

<snip>

> IP. Not the BR itself. This is a critical point (architecturally) to

If this is true, we do not have to do anything special.

> also presents itself to IP as a single IP subnet that has the normal

I think there are two MANET implementation models.
One is hiding MANET form IP, e.g. a sub-IP MANET model. This is more or less
out-of-scope for IETF.
The other model is described in this document. Now we have to face the
reachability issues. I think the MANET Router shall hide this for IP hosts
and non-MANET routers. If this is arranged by using a single IP subnet or
using another addressing model is solution space.
 
There might be a discussion on supporting connectivity to (mobile) hosts via
the MANET Interface. I will post on this separately.

Teco.

---

From: "Templin, Fred L" <[email-masked]>
Date: Tue, 4 Dec 2007 09:06:51 -0800

> -----Original Message-----
> From: Thomas Narten [mailto:[email-masked]] 
> Sent: Tuesday, December 04, 2007 5:44 AM
> To: [email-masked]
> Subject: [Autoconf] comments on draft-ietf-autoconf-manetarch-07.txt
> 
> 2007-11-30 review of -7
> 

I agree with Thomas, and I believe also confirmed by Teco.
IMHO, this is an INT area document (not RTG) and it needs
to speak to the terminology of the INT area.

Thanks - Fred
[email-masked]

---

From: Thomas Narten <[email-masked]>
Date: Tue, 04 Dec 2007 14:45:23 -0500

> Maybe better definition could help.

Well, yes! :-)

> interface types, like NBMA and P2MP.

No. NBMA is a link type, not an interface type. IPoverATM, for
example, looks to IP just like a traditional IP-friendly link. There
is a layer of software between IP and ATM that emulates the necessary
services that IP needs (like ARP/broadcast). The ATM "interface",
however, is just a normal interface. The IP layer does not know about
the quirks of ATM and doesn't need to worry about the "challenges" in
semantics in order for IP to work.

Another way to view things. Stuff that is "interface-specific" is
normally implemented by a device driver (for the specific link layer),
and not by IP.

> Now we want to define another.

The term "interface" is also well-known outside of MANET. If you look
at RFC1122, for example, interface is about the interface beween
layers (e.g, between IP and the link layer). The more general term
"interface" (in terms of network software) is the data abstraction
used to access the facilities of a particular network.

> If this is true, we do not have to do anything special.

Well, I'm trying to understand whether this is the case or not.

> One is hiding MANET form IP, e.g. a sub-IP MANET model. This is more or less

This could be done in the IETF, and maybe this is  a direction the WG
may want to pursue. But is this even a model the WG is currently
considering?

IMO, this is the _obvious_ model to implement, or rather, if any other
model is needed, the case first needs to be made why the above model
is not good enough (or better).

> The other model is described in this document.

And what model is that? The problem I have currently is I don't
understand the scope of the problem. What is the abstraction. Where is
the MANET-specific stuff implemented, and what is the boundary between
this and what IP sees?

E.g., the MR model suggests that I can have an ethernet interface and
two manet interfaces. Where does the MANET stuff sit (just above the
two MANET interfaces?) What part is visible to IP (and why?) Does the
MANET specific stuff get exported across the Ethernet? Why or why not?

Very basic questions, but the document doesn't make this clear at all.

> Now we have to face the reachability issues. I think the MANET
> Router shall hide this for IP hosts and non-MANET routers.

Hide it from whom? What is the scope of where this information is
supposed to be exported? It's not good enough to say "within the
MR". Where within the MANET router?  What part of the MR code is
"normal, unmodified IP" and what part has to be MANET-aware?

Thomas

---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 04 Dec 2007 13:52:34 -0800

Thomas Narten wrote:
[...]
>>> You really (I think) need to define an abstraction that defines
>>> an link type of "manet" that handles all the "interesting" 
>>> characteristics of MANETs (like non-transitive connectivity) but
>>> that also presents itself to IP as a single IP subnet that has
>>> the normal properties.
> 
>> One is hiding MANET form IP, e.g. a sub-IP MANET model. This is
>> more or less out-of-scope for IETF.
> 

As a member of this WG I can say that I currently consider a model where
the MANET protocol is run at sub-IP and offers a IP-friendly MAC
already.   I mean the sub-IP may run MANET, or may not.  I'm interested
in the interface that sub-IP provides to my stack, and needing that
interface to be a Ethernet MAC.

I would also like to learn from other WG members.

Alex

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---

From: "Templin, Fred L" <[email-masked]>
Date: Tue, 4 Dec 2007 14:08:52 -0800

> From: Alexandru Petrescu [mailto:[email-masked]] 
> Sent: Tuesday, December 04, 2007 1:53 PM
> To: Thomas Narten
> Cc: [email-masked]
> Subject: Re: [Autoconf] comments on 
> draft-ietf-autoconf-manetarch-07.txt
> 
> Thomas Narten wrote:
> [...]

We talk about sub-IP MANET model in 'draft-templin-autoconf-dhcp'
(which contrary to the name is not only about dhcp solutions).
It makes life nice for IP, but may not be sufficient for MANETs
made up of heterogeneous link types.

Fred

---

From: "Bound, Jim" <[email-masked]>
Date: Tue, 4 Dec 2007 22:08:50 +0000

Teco,

MANET is not a "link-type" as Thomas N relays it is an interface but the choice of calling it that could be optimized, though it works for me as input to the WG.  For example MANET interface will have different L2 drivers to those link types for 802.11g, 802.11s, Military Classified L2's, GSM, CDMA, and ones not invented yet.  I think the bug is in the orginal 2461 ND spec using the term NBMA and back to ATM networks.  NBMA is not a link type but an architecture approach to operate IP over links.  MANET is like NBMA in the abstract but completely different.  MANET is really to me a reference architecture for an implementation of a network architecture and that is new to us in the IETF except in the MANET WG arena.  The next order derivative to MANET the interface is how it approaches routing, advertisements, solicitations, etc.  That is what must be written in a manner that it is comfortable and clear to the IETF IP community.  To me the spec is fine but as you I live in the MANET world almost daily as architect and one who is concerned with products and time to market for MANET.  We probably need to make it more IP community friendly and that will help the market too to adopt this spec.

/jim

> From: Teco Boot [mailto:[email-masked]]
> Sent: Tuesday, December 04, 2007 11:55 AM
> To: 'Thomas Narten'; [email-masked]
> Subject: RE: [Autoconf] comments on
> publication.
> > It is still to vague/muddy on the key architectural points
> that it is
> > supposed to explain.
> >
> I think it is easy to understand that a MANET Interface is an
> interface that may suffer from certain link characteristics.
> We have similar kind of interface types, like NBMA and P2MP.
> Term MANET Interface is well known, e.g. it is used in MANET
> Routing Protocol documents, including the OSPF ones.
>
> Maybe term Semi-Broadcast Interface (SBI) should be removed,
> this is about the link characteristics. Hint for editer:
> Change SBI into MANET and some textual cleanup will do.
>
>
> <snip>
>
> >    Interface
> > What I thought the MANET architecture would provide is a
> description
> One is hiding MANET form IP, e.g. a sub-IP MANET model. This
> is more or less out-of-scope for IETF.
> The other model is described in this document. Now we have to
> face the reachability issues. I think the MANET Router shall
> hide this for IP hosts and non-MANET routers. If this is
> arranged by using a single IP subnet or using another
> addressing model is solution space.
>
> There might be a discussion on supporting connectivity to
> (mobile) hosts via the MANET Interface. I will post on this
> separately.
>
> Teco.
>
>
>

---

From: "Teco Boot" <[email-masked]>
Date: Tue, 4 Dec 2007 23:27:08 +0100

> interface that

OK, now we have something as "IP-friendly". Fully meshed, full broadcast. If
this is the case, we can use IP protocols as is.

In reality, some links are not that friendly. I think this is explained in
the MANET Architecture document quite well, but using some wrong terms. 
On wrong terms: For example section 4 "MANET Interface Characteristics" is
about the links. It should be "MANET Link Characteristics".

I think it is useful keeping the term MANET Interface, being used as "a
MANET Router's attachment to a MANET link". 
I am not sure if we should use MANET Interfaces for hosts.

I would like to use the RFC4861 based definition:
      interface       - a node's attachment to a link.
Any objection to:
      MANET Interface - a MANET Router's attachment to a MANET link
?

> Well, I'm trying to understand whether this is the case or not.

I think it is obvious that if MANET is sub-IP, IP is not aware and all
protocols run well.

If you mean you want to know why this is a bad idea in some cases, I agree
that this should be described. It is, in the bottom of Section 6: MANETs'
Place in the Network Stack.

This is also described in RFC2501 5. IP-Layer Mobile Routing.
Maybe a reference to this section would help.

> that

I think there are multiple models and there are valid reasons for this.

> And what model is that? 

L3 MANET.
I agree the readability of the document would be improved if both MANET
models are introduced very early in the document.

> The problem I have currently is I don't
> supposed to be exported? 

Discussed in 5.3.  Routers and Hosts in a MANET.

Maybe we shall update RFC4294 IPv6 Node Requirements one day and add a
section on MANET.

> It's not good enough to say "within the

Good questions, but more related to a Router Architecture. Do we work on
this or is it up to the implementers?

Teco.

---

From: "Templin, Fred L" <[email-masked]>
Date: Tue, 4 Dec 2007 15:38:33 -0800

Teco,

>       MANET Interface - a MANET Router's attachment to a MANET link

That is what it says now in 'draft-templin-autconf-dhcp',
so I have no objections.

Fred

---

From: "Bound, Jim" <[email-masked]>
Date: Wed, 5 Dec 2007 01:17:13 +0000

I agree with the update and very clear and distinct for autoconf work.  It also kills the NBMA issue I have in 4861.

/jim

> From: Templin, Fred L [mailto:[email-masked]]
> Sent: Tuesday, December 04, 2007 6:39 PM
> To: Teco Boot; Thomas Narten
> Cc: [email-masked]
> >       MANET Interface - a MANET Router's attachment to a
> MANET link ?
>
> That is what it says now in 'draft-templin-autconf-dhcp', so
> I have no objections.
>
> Fred