[manet] Re: MANET WG Charter and MANET Internetworking

Thanks Chris. So, for MANET routers that configure an OMNI interface packets sent
over the OMNI link do not have the Hop Limit/ TTL decremented in the overlay even if
there may be many hops in the underlay. That is why IPv6 ND works unmodified; the
messages always come through with Hop Limit 255 no matter how many hops they
took in the underlay.

Fred

From: Christopher Dearlove <[email protected]>
Sent: Thursday, July 17, 2025 1:20 PM
To: Templin (US), Fred L <[email protected]>
Cc: Juliusz Chroboczek <[email protected]>; manet <[email protected]>; [email protected]
Subject: [EXTERNAL] [manet] Re: MANET WG Charter and MANET Internetworking

EXT email: be mindful of links/attachments.


A MANET router is an IP router. That was the conclusion from the Autoconf group. And it was a real sticking point in producing something that both worked (because radio connectivity is not transitive, despite some people wanting to assume ir is, contrary to the laws of physics) and fitted the IP router/host model that was non-negotiable.

So if a MANET router is an IP router, if it forwards an IP packet it’s going to reduce its TTL. Should be fine, plenty of hops to spare if you start at 255. But - and it’s been a while since I saw this discussion, so it’s not just details I’m forgetting - the MANET is not going act to like a simple subnet in at least that way, even if addressed that way. Does that matter? Maybe not. But  I recall some people thinking it might, especially if not just starting TTL at 255 (or another large value). Just another of those little details to get right. (Ideally there should be stuff in Autoconf records about these things - what was discussed and what conclusions reached or not reached - but I think it would be optimistic to assume that,)



On 17 Jul 2025, at 18:11, Templin (US), Fred L <[email protected]<mailto:[email protected]>> wrote:

-----Original Message-----
From: Juliusz Chroboczek <[email protected]<mailto:[email protected]>>
Sent: Thursday, July 17, 2025 9:06 AM
To: Templin (US), Fred L <[email protected]<mailto:[email protected]>>
Cc: Donald Eastlake <[email protected]<mailto:[email protected]>>; manet <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>
Subject: [EXTERNAL] Re: MANET WG Charter and MANET Internetworking


Julien,

Julius.  Completely different emperors.

Juliusz, apologies for that typo - an unintentional mistake on my part.


we need to get out into the open what the alternatives are and what
their advantages or limitations are before we can settle on charter
text.

I'd expect things to happen the other way around (charter first, solutions
later), but okay.

I think there is room to have both stateless and stateful autoconfiguration in
the charter - it might make everyone happy.


The two autoconfiguration alternatives are 1) stateless based on SLAAC,

SLAAC doesn't work with routers.  We've all tried, but it cannot possibly
work.

(There's no mechanism to break RA loops, so if a MANET router ever needs
to send an RA, say to an attached stub network, you lose.  You can design
all sorts of workarounds, such as those proposed by the SNAC group, but
I personally find them brittle and distasteful.)

I used the term SLAAC in an imprecise way. I did not mean SLAAC per the letter
of the law of RFCs 4861/2 which involves RS/RA messaging. Rather I meant that
if a MANET router already has a statistically unique 8 octet quantity that it can
use as an interface identifier, and it discovers through some means a /64 prefix
owned by a current Internet access point, then it should be able to statelessly
put 8+8 together to form a unique and globally routable IPv6 address. If all
routers in the MANET did this, then there may be temptation to consider the
MANET as an IPv6 subnet - but the multihop nature of the MANET would make
it a "multilink subnet" and RFCs 4903 and 5942 would have to be consulted.


stateful based on DHCPv6

I'm fairly sure you need state, but I don't see how that entails DHCPv6.

Can we conceptualize an 8+8 address autoconfiguration scheme where
the only "state" is the MANET router's unique interface identifier and
the current set of IPv6 prefixes advertised by a current working set of
Internet access points? This information could be propagated to all
MANET routers by the MANET routing protocol.


Here again, an overlay multilink network interface is needed to
coordinate the multiple interfaces.

I must have missed a step.  Why is that required?

To give all MANET routers the appearance of being on-link with the current
set of Internet access points and each other even if they may be multiple
hops away in the MANET underlay. The alternative in the DHCPv6 case is to
have all MANET routers also act as DHCPv6 relay agents, but that might not
work so well in dynamic MANETs with rapidly changing topologies.

Thank you - Fred


-- Juliusz

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