On 1/26/2015 8:41 AM, Dearlove, Christopher (UK) wrote:
Joe Touch
Routing is the transitive closure of unidirectional reachability.
You need known and usable unidirectional reachability. If A can reach
B, but A has no idea of that, then that's not usable for routing.
That's also known. Unidirectional links have been part of routing for a
very long time.
Yes, there could be an odd situation where IP HELLO datagrams can
transit a link where other IP datagrams cannot, but in that case RFC6130
would determine forwarding entries that wouldn't do much good.
(That is in fact a real problem when using IEEE 802.11 as your L2, but that's
not the point here.)
802.11 has a problem when *L2* reachability signals don't translate to
L3 reachability. RFC6130 gets around that by using control messages that
are sent inside L3.
Unless you have some sort of filter in place, if HELLO in IP gets there
then IP gets there.
And there's another issue that happens in RFC 6130 and ad hoc
routingprotocols. You don't know who can hear you until they let you know.
Some routing protocols assume bidirectional communication, i.e., if you
can send an IP datagram to me then I can send one to you. But that's
only a subset of routing protocols; routing protocols that support
unidirectional links have also been around for a long time.
> You find them using local broadcast.
The PILC doc explains why this is a bad idea unless L2 is known to
support broadcast. The L2 you're describing fails that assumption.
That RFC does imply that control message reachability implies IP
reachability.
Not until you've confirmed a return path, so, no to the above.
The RFC implies that control reachability implies IP reachability.
It does not imply that unidirectional reachability implies bidirectional
reachability. When B receives a HELLO from A, then B knows it can get IP
datagrams from A (that's a leap that the doc makes because it HELLOs are
sent inside IP datagrams).
No, local reachability information does not magically imply global
reachability information; that's what a routing protocol determines and
exchanges.
-----
It might help us understand what you want to do if you just say it:
A- are you trying to describe an L2?
B- are you trying to describe a L2 routing protocol?
C- are you trying to describe an L3 routing protocol?
Please pick *one* and start there. If you want to do (B) for an (A) that
hasn't been described, then start with (A).
Again, I still have not seen anything yet that's new.
Also, please do this in an update to your draft. You're asking us to do
your work at this point.
Joe
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