Subject: [manet] OLSRv2 - Routable Address

From: Teco Boot <[email-masked]>
Date: Tue, 27 Jul 2010 15:04:12 +0200

Question on OLSRv2: why would an anycast address not be a routable address?

Teco.

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From: Henning Rogge <[email-masked]>
Date: Wed, 28 Jul 2010 17:16:15 +0200

> Question on OLSRv2: why would an anycast address not be a routable address?
I think an anycast address would be just an attached network in the TC...

Henning Rogge

-- 
"Wo kämen wir hin, wenn alle sagten, wo kämem wir hin, und niemand
ginge, um einmal zu schauen, wohin man käme, wenn man ginge." (Kurt
Marti)

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From: Teco Boot <[email-masked]>
Date: Wed, 28 Jul 2010 20:09:10 +0200

> I think an anycast address would be just an attached network in the TC...

Sure. 

I can't see why the following restriction exist (page 6):
    ... Broadcast, multicast
    and anycast addresses, and addresses which are limited in scope to
    less than the entire MANET, MUST NOT be considered as routable
    addresses.

And (page 27):
   A router's Attached Network Set records information about networks
   (which may be outside the MANET) attached to other routers and their
   routable addresses.
/ (page 56):
   ... Only appropriate Routing Tuples
   (in particular only those that represent local links or paths to
   routable addresses) need be reflected in IP's routing table.
This would exclude anycast.

Handling anycast as routable could have side-effects. I didn't check draft on this.
Ideas?

Teco

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From: "Dearlove, Christopher (UK)" <[email-masked]>
Date: Thu, 29 Jul 2010 09:49:55 +0100

> less than the entire MANET, MUST NOT be considered as routable

Because the protocol can't handle them - it's a unicast routing
protocol. Considering any as a routable address causes problems.
(The limited scope one causes a different sort of problem.) Some
of these problems may be possible to overcome, but the question
is whether in the base protocol or an extension. In the case of
multicast addresses an extension is clearly called for for
various reasons (one being that SMF might do the job). By
excluding multicast as routable in the base spec, this leaves
the maximum amount of freedom for such an extension. (An extension
can always say "you know these addresses you were told to ignore,
now you can do this with them". It generally can't say "you know
those addresses you were told to do X with, now do Y instead".)

> (page 56):

> Currently OLSRv2 does not claim to support anycast, and thie
> reflects that. Note that it says "reflected in IP's routing table"
> not "present in IP's routing table". Something else could put
> such addresses in.

However extension to handle anycast addresses appears, at first
sight, to be relatively straightforward. Consider three classes
of address: routable (excluding anycast), anycast and other.
(This trerminology for this email only.) Then we allow anycast
addresses as attached networks, but not as interface addresses,
i.e. we relax the restriction on attached addresses only to be
"routable or anycast" rather than "routable". Other restrictions
are unchanged. (Attached addresses can already be shared by
routers.) Are there any other addresses that could be called
"attachable" beyond (unicast) routable and anycast? And note
that I said "at first sight" above, I reserve the right to
realise I've made an error and this idea doesn't work.

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From: Henning Rogge <[email-masked]>
Date: Thu, 29 Jul 2010 12:52:08 +0200

On Thu, Jul 29, 2010 at 10:49, Dearlove, Christopher (UK) > However
extension to handle anycast addresses appears, at first
> addresses as attached networks, but not as interface addresses,
I agree to this, this should work fine, most likely even without
changing the code (except the filter code that prevents setting up the
attached network addresses.

(our OLSRv1 implementation can handle anycast as HNA, just because
noone thought about implementing a filter to prevent them being set in
the configuration).

> realise I've made an error and this idea doesn't work.
Multicast is routable, but it's a special case that requires
additional work and information. So we should not allow it in the
normal attached network case.

Henning Rogge

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From: "Dearlove, Christopher (UK)" <[email-masked]>
Date: Thu, 29 Jul 2010 12:01:45 +0100

We need to rely on more than just luck with filters in a
specification. Roughly speaking this would

(a) Leave routable defined as is (excluding anycast).
(b) Define a new category of attachable, also administratively
    defined. Routable addresses SHOULD be attachable. Anycast
    addresses MAY be attachable. (There is, I think, no reason
    to make either of those stronger.)
(c) Local attached addresses MUST be attachable (rather then
    routable). Other uses of attached addresses modify accordingly
    (such as received message sanity checking rules).
(d) Attachable addresss can be put in the routing table.

Now are there any problems with this?

(Conceptually I quite like having the rules for attached addresses
separate from the rules for interface addresses, as they already
have reuse differences - interface addresses must be unique to a
router, attached addresses do not need to be.)

-- 
Christopher Dearlove
Technology Leader, Communications Group
Networks, Security and Information Systems Department
BAE Systems Advanced Technology Centre
West Hanningfield Road, Great Baddow, Chelmsford, CM2 8HN, UK
Tel: +44 1245 242194  Fax: +44 1245 242124

BAE Systems (Operations) Limited
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Registered in England & Wales No: 1996687

-----Original Message-----
From: Henning Rogge [mailto:[email-masked]] 
Sent: 29 July 2010 11:52
To: Dearlove, Christopher (UK)
Cc: Teco Boot; MANET IETF
Subject: Re: [manet] OLSRv2 - Routable Address

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