Subject: [Autoconf] On the LL issue

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Mon, 27 Jul 2009 17:07:53 +0200

Hi all,

	After (silently) hearing all the discussions on the LL issue during the
meeting, here is my understanding (just to check if I got it right):

	- Ensuring uniqueness of LL addresses in a MANET is hard, because of
the dynamic nature of MANET links (i.e. a neighbour now might not be my
neighbour anymore 1ms after).
	- IPv6 specs state that any node MUST have an LL address configured.
They don't say this address has to be used. Therefore, one approach is
autoconf to propose a way of configure an LL address (maybe as simple as
just using EUI64 from MAC addresses), but then warn routing protocols
and applications not to use LL in MANETs.
	- Routing protocols might use ULAs or global addresses to work.
However, there seem to be protocols that say that LL MUST be used (some
routing protocols, as Teco commented, or just sending RAs, RS).
	- One of the proposals in the room was to focus autoconf on just
working on a practical way of configuring unique ULAs/global addresses
(it was also recommended not to make a distinction in the document) and
forget about LL.

	This is my summary, please comment on those things I might have got
wrong.

	Now, my opinion about how to progress (I'm listing the approaches that
could be on the table, ordered by my personal preference) is the
following (I'm just trying to answer to chairs' request to comment on
the ML, since I'm voted against making DT document a WG document):

	- 1st preference: although it'd be easier to forget about LLs, we
should try to do something better. We may try to come up with something
that ensures that LL addresses configured in a MANET are not only unique
within the link-scope (as required by IPv6 specs), but also within the
MANET scope (whatever scope this is, we have to agree on that scope
anyway even for ULA uniqueness). This would make the solution harder,
but it would not break anything I could think of now. My fear is that by
not paying attention to LL, we may end up forgetting about some protocol
that is broken (or requires to be revised) in MANETs.

	- 2st preference: autoconf just focuses on autoconfiguration of
ULAs/global addresses, BUT does NOT forget completely about LLs. We may
just recommend using EUI64-like SLAAC for LLs and comment that due to
the MANET characteristics, 'users' of LL addresses might not assume that
LLs are unique within the link (because the link is very dynamic). This
would not preclude people from using LLs.

	- 3rd preference: we forget completely about LLs and just focus on
ULAs/globals. I'd personally prefer not going there.

	Comments?

	Thanks,

	Carlos

-- 
Carlos Jesús Bernardos Cano     http://www.netcoms.net
GPG FP: D29B 0A6A 639A A561 93CA  4D55 35DC BA4D D170 4F67

---

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 27 Jul 2009 18:23:16 +0200

> would not preclude people from using LLs.

I agree with this approach.  An AUTOCONF mechanisms auto-configures 
ULAs/globals by assuming link-local addresses are already there and 
ensured existence.  AUTOCONF mechanism would not auto-configure 
link-local addresses, just reuse them.

E.g. the src address of the first AUTOCONF packet is a link-local 
address, pre-defined in earlier RFCs.

> ULAs/globals. I'd personally prefer not going there.

Alex

---

From: "Teco Boot" <[email-masked]>
Date: Mon, 27 Jul 2009 18:37:22 +0200

Hi Carlos,

Comments and questions inline.

|-----Oorspronkelijk bericht-----
|Van: [email-masked] [mailto:[email-masked]] Namens
|Carlos Jesús Bernardos Cano
|Verzonden: maandag 27 juli 2009 17:08
|Aan: [email-masked]
|Onderwerp: [Autoconf] On the LL issue
|
|Hi all,
|
|	After (silently) hearing all the discussions on the LL issue
|during the
|meeting, here is my understanding (just to check if I got it right):
|
|	- Ensuring uniqueness of LL addresses in a MANET is hard, because
|of
|the dynamic nature of MANET links (i.e. a neighbour now might not be my
|neighbour anymore 1ms after).

Do you think it is more easy to come up with unique globals?
What makes the difference?

|	- IPv6 specs state that any node MUST have an LL address
|configured.
|They don't say this address has to be used.

Some protocols clearly specify link-locals MUST be used.
ND RA is an example. OSPFv3 (with the MANET extensions) is another.

| Therefore, one approach is
|autoconf to propose a way of configure an LL address (maybe as simple as
|just using EUI64 from MAC addresses), but then warn routing protocols
|and applications not to use LL in MANETs.

I do not see any reason that we cannot use link-locals for MANET routing
protocols. It provides exactly what is needed: routing protocol packets
shall not be forwarded. Using link-locals provides this. We asked for a
link-local multicast address (RFC5498). And we got one !!!

|	- Routing protocols might use ULAs or global addresses to work.
|However, there seem to be protocols that say that LL MUST be used (some
|routing protocols, as Teco commented, or just sending RAs, RS).

RS does not have the link-local requirement.

Regards, Teco.

|	- One of the proposals in the room was to focus autoconf on just
|working on a practical way of configuring unique ULAs/global addresses
|(it was also recommended not to make a distinction in the document) and
|forget about LL.
|
|	This is my summary, please comment on those things I might have
|got
|wrong.
|
|	Now, my opinion about how to progress (I'm listing the approaches
|that
|could be on the table, ordered by my personal preference) is the
|following (I'm just trying to answer to chairs' request to comment on
|the ML, since I'm voted against making DT document a WG document):
|
|	- 1st preference: although it'd be easier to forget about LLs, we
|should try to do something better. We may try to come up with something
|that ensures that LL addresses configured in a MANET are not only unique
|within the link-scope (as required by IPv6 specs), but also within the
|MANET scope (whatever scope this is, we have to agree on that scope
|anyway even for ULA uniqueness). This would make the solution harder,
|but it would not break anything I could think of now. My fear is that by
|not paying attention to LL, we may end up forgetting about some protocol
|that is broken (or requires to be revised) in MANETs.
|
|	- 2st preference: autoconf just focuses on autoconfiguration of
|ULAs/global addresses, BUT does NOT forget completely about LLs. We may
|just recommend using EUI64-like SLAAC for LLs and comment that due to
|the MANET characteristics, 'users' of LL addresses might not assume that
|LLs are unique within the link (because the link is very dynamic). This
|would not preclude people from using LLs.
|
|	- 3rd preference: we forget completely about LLs and just focus on
|ULAs/globals. I'd personally prefer not going there.
|
|	Comments?
|
|	Thanks,
|
|	Carlos
|
|--
|Carlos Jesús Bernardos Cano     http://www.netcoms.net
|GPG FP: D29B 0A6A 639A A561 93CA  4D55 35DC BA4D D170 4F67

---

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Mon, 27 Jul 2009 18:53:59 +0200

Hi Teco,

	More inline...

> What makes the difference?

Well, depending on the solution (this is solution space) it might be the
same, I agree, but from a high level viewpoint, ensuring uniqueness for
64bits is harder than for 128 :-D

> ND RA is an example. OSPFv3 (with the MANET extensions) is another.

Agree, I think I mentioned this on my mail.

> link-local multicast address (RFC5498). And we got one !!!

Well, using link-local is one approach. Using ULAs/globals with Hop
Limit=1 would be another. I'd also like to use LLs, but if it makes my
life easier to use ULAs/globals, I'd not have a problem using them
either.

> RS does not have the link-local requirement.

Agree, my mistake.

Carlos

---

From: "Charles E. Perkins" <[email-masked]>
Date: Mon, 27 Jul 2009 14:20:30 -0700

Hello Teco,

> What makes the difference?

For global addresses or ULAs, we can use those addresses in
packet headers of protocol messages that can be forwarded.
Link-local addresses cause packets to not be forwardable.

Since global uniqueness is a non-local property, in some
situations we do have to forward packets to insure global
uniqueness.

Regards,
Charlie P.

---

From: "Teco Boot" <[email-masked]>
Date: Tue, 28 Jul 2009 07:47:30 +0200

Hi Carlos,

More on:
|> Do you think it is more easy to come up with unique globals?
|> What makes the difference?
|
|Well, depending on the solution (this is solution space) it might be the
|same, I agree, but from a high level viewpoint, ensuring uniqueness for
|64bits is harder than for 128 :-D

OK, let's go for a /4 for MANET local :-).
But then, any idea how we can use the 124 bits for a global?

So with my foots on the ground, we have 62 bits for random.
If we run DAD on Interface-ID (or skip this for reasons), 
we are done for link-locals, ULA and globals. The latter for
whatever /64 prefix is delegated for usage in the MANET.
See Fred's doc App.A for discussion on DAD.

Teco.

---

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Tue, 28 Jul 2009 09:14:50 +0200

Hi Teco,

> See Fred's doc App.A for discussion on DAD.

I know, and I fully agree that it'd be enough to use random IID. You can
also check
http://tools.ietf.org/html/draft-soto-mobileip-random-iids-00, it is
also a good reading.

Carlos