[Babel-users] babel and zeroconf

[Juliusz Chroboczek]

>  getting proper WAN-wide name registration and defending is _hard_.

Yes, if you want to be distributed.  You can always fake it with
a centralised server.

>  it takes about _three years_ to get it right - as no less than three
> of us found out for samba.

Yeah, but you needed to be bug-compatible with another system.  Doing
it from scratch would have been easier.

>  i just did some research on zeroconf a couple of hours ago: it turns
> out _again_ to be an extension of DNS which is very ironic given
> people's aversion to NetBIOS and "network neighbourhood" for being so
> "chatty"

AFAIK, Zeroconf was inspired by Appletalk, not NetBIOS.  Your point
still stands, though, as Appletalk was also criticised for being too
chatty.

>>  In a mesh network, the notion of link doesn't really
>>  exist, so zeroconf will give mixed results.

> ... this i don't follow.  you're using terms that have specific
> meanings with which i'm not yet familiar, and, as it's an area i
> really do need to understand, i'd very much appreciate some pointers /
> elaboration.

Sure.  In traditional (wired) networking, a link is a set of
interfaces that can communicate without going through a router.  It
used to be just a cable, nowadays it's usually a set of cables bridged
together.

In both IPv4 and IPv6, you usually assume that if a node belongs to
the same subnet prefix as you do then it is on the same link, and you
may speak to it directly (ignoring unnumbered links and multiple
prefixes per link for now).  In other words, you encode topology
information within the bits of the address.

Obviously, this is not the case for mesh networks, where the topology
varies over time and does not correspond in any way to the address
allocation.

> in particular, what does - or doesn't - babel provide for "mesh networks" ?

Babel is a routing protocol that, in its basic form, does not make any
assumptions about how prefixes map to links.  Hence, it will work on
any network topology -- wireless mesh, classical wired network --, but
might not be optimally efficient.

Babel can be made to be efficient on wired networks, but this requires
a little bit of per-node configuration.  Since most of our nodes are
wireless, and at any rate the inefficiency incurred by using
out-of-the-box Babel on wired networks is slight, that's satisfactory.

The only assumption that Babel makes about the underlying network is
that link-local multicast is able to reach all neighbours.  Hence, in
its current form, it will not work on non-broadcast (NBMA) networks,
such as ATM.

>  mm? *quizzical*.  i thought ipv6 didn't do multicasting?

IPv6 multicasts just fine.  However, non-local multicast requires
multicast routers, and Babel doesn't route multicast right now.

> the lowest speed network is a digital radio modem, with something
> like a 10 mile range (with TCP/IP on it).

How does that Simpsons line go again?  Mmmh... 800MHz.

> the other ones we have yet to specify but candidates include
> GPRS/EDGE or maybe 3G, and WIMAX or some other adhoc high speed
> networking.

What do you mean by ``ad-hoc''?  If you're using the term to mean that
stations can communicate between themselves, then WiMAX certainly
isn't, it's strictly a point-to-multipoint technology.  (Which is
something that Babel will handle beautifully, by the way.)

> please don't ask why all that's needed :)

Please do tell!

> so i am suddenly extreemely interested in decent and versatile routing
> software that can help here!

Babel is certainly versatile, and I like to think it's decent.  It can
deal with multiple interfaces, which appears to be what you are mainly
concerned with.

But you'll really need to tell us more about the network architecture
you're envisioning.  Whether Babel or some other technology is best
depends on a lot of factors, notably what kind of hand-off times are
tolerable, whether you're interested in multi-hop routing, how large
is your power budget, and whether you can count on link-layer notifications.

> so i will have - some time in the next few weeks - suddenly plenty of
> time on my hands to focus on this.  and perhaps some funding available
> too.

Cool.

                                        Juliusz