[Babel-users] Version 1.6.0

[Ondrej Zajicek]

On Sun, May 01, 2016 at 03:32:58PM +0200, Toke Høiland-Jørgensen wrote:
> Ondrej Zajicek <santiago at crfreenet.org> writes:
> 
> >  - in some cases (e.g. babel_handle_route_request()), check for plen == 0
> >    or check if prefix is IPA_NONE is used where check for AE 0 should be
> >    used instead. Note that these are two different cases - there is the
> >    default route ::/0 (with AE 2), which is a regular route, and there is
> >    'wildcard' AE 0, which represent all routes.
> 
> This was actually deliberate on my part: I have considered the different
> AEs as solely a matter of encoding on the wire, and not carrying any
> significance as to the semantics of the prefix. I.e. and update with AE
> 0 and no prefix and one with AE 2 encoding ::/0 are identical in my
> reading.

There is an implied semantics of address family:

   The address family of an address is either IPv4 or IPv6; it is
   undefined for AE 0, IPv4 for AE 1, and IPv6 for AE 2 and 3.

Obviously, there is a difference between AE 1 encoding 0.0.0.0/0 and
AE 2 encoding ::/0, therefore AE 0 cannot be identical to both of them.


> If this is not the case, I think the RFC needs to specify what, exactly,
> is meant by a "wildcard address". I've always thought of ::/0 as the
> wildcard address; and doesn't "default route" also mean "wildcard
> route"?

'default route' is just a name for the least specific route, i.e. 0.0.0.0/0
or ::/0, but it is a route like any other. While meaning of AE 0 is more
like unspecified/any route. Its exact meaning depends on specific TLV:

IHU TLV (address implied/irrelevant):

  it MAY be 0 if the TLV is sent to a unicast address, if the association
  is over a point-to-point link, or when bidirectional reachability is 
  ascertained by means outside of the Babel protocol.

Update TLV (all routes):

  AE MAY then be 0, in which case this Update retracts all of the routes
  previously advertised on this interface.

Route Request TLV (all routes):

  The (AE) value 0 specifies that this is a request for a full routing
  table dump (a wildcard request)


> >  - babel_read_update() - does BABEL_AE_IP6_LL make sense?
> 
> Not sure it makes much sense to announce a route for a link-local
> address, but I suppose it could be used to set a router ID? (Not sure
> why anyone would do that, but it would not technically be out of spec).

Well, most routing protocols explicitly forbid to propagate link-local
routes. So this may be omission in RFC 6126, OTOH it might make sense
on ad-hoc wireless networks, where everybody is in one network but there
is no full mutual visibily.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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