[radvd-devel-l] poor man's routing daemon

Lukasz Stelmach stlman at poczta.fm
Sat Aug 20 17:43:14 EDT 2011

W dniu 20.08.2011 19:37, Sergei Zhirikov pisze:

> --- On Sat, 8/20/11, Lukasz Stelmach <stlman at poczta.fm> wrote:
>> But... is there any way to control radvd depending on uplink
>> availability?
> As far as radvd is concerned, there is no such thing as "uplink".

Yes I know.

> There is local network and prefixes to be advertised in it.
> Although, radvd does have a "bonus" feature that allows to
> change the advertised prefixes dynamically in case of 6to4
> tunnels, which may or may not be useful to you (you didn't
> mention what kind of tunnels you are using).

I've got "ordinary" tunnels, to SixXS POP.

>> I've got two networks each with a single IPv6 uplink
>> tunnel and I would like radvd to stop sending advertisments (or start
>> sending ones with zero times) when the tunnels stop working.
> If you really want that you could rewrite the radvd configuration
> file when necessary.

I know that too, but I don't like mangling config files if there
is an option to avoid it.

> But don't forget that advertising zero lifetimes
> will not reset the lifetimes advertised in the past
> (unless the advertisements are authenticated).

If I set "normal" lifetimes to about 5-15 minutes then prefixes
would be invalidated soon enough for me if only radvd stops
pushing hosts.

>> It's definitely routing daemon's job
> It's definitely not. Routing daemon couldn't care less about
> advertising prefixes.

OK. This time it is probably my lack of practical experience in
working with larger networks.

> The two things it cares about are talking to fellow routers and
> updating local routing tables.

So let me explain. I consider hosts to be very similar to
routers. Both have routing tables both need information to populate
those tables. No ordinary desktop machine runs BGP daemon, true.
What I am seeking is a means of control of hosts' routing tables.
Especially now when I (we?) use dual-stack hosts and tunnels which
may be down while IPv4 routing is still operational (just like
routers are passed information via BGP that a particular route is
down). Disabling the default IPv6 route on a host is the best way
to avoid delays when choosing between A and AAAA addresses provided
by DNS.

Of course there are other ways than changing router advertisements,
I was (am) curious if radvd radvd provides any viable solution to
my problem.

>> but in setups like these radvd is a de facto poor man's routing
>> daemon.
> I can't imagine how one could use radvd instead of a routing
> daemon. They perform different functions, use different protocols,
> they have basically nothing in common. May be I'm missing
> something here, could you please elaborate?

In the simplest setting (one uplink, one router, one LAN)
radvd+hosts act exactly the same way as routed broadcasting RIP
messages to hosts running RIP client listening to them (nb. Win98 or
even 95 had a RIP client). Routing daemons and protocols provide
enough information to build a complex routing table but for a LAN
with a single gateway information radvd provides is just enough.

Było mi bardzo miło.               Czwarta pospolita klęska, [...]
>Łukasz<                 Już nie katolicka lecz złodziejska.  (c)PP

Najwieksza baza samochodow nowych i uzywanych
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