[OLSR-users] olsrd with 2 networks
Wed Feb 8 01:10:32 CET 2006
Bernd Petrovitsch wrote:
> On Tue, 2006-02-07 at 12:47 +0100, Kosta Welke wrote:
> The interface will have exactly one IP address.
> And actually I'm thinking on configuring /32 on the interfaces IP
> address because:
> - I don't have to explicitly delete the automatically added route
I do not completely understand what you mean, but please note that olsr
automatically deletes routes it created after process termination. (At
least, thats what I observed. Please correct me if I'm wrong or if this
is not 100% reliable)
> This may be a Linux-only problem and it doesn't hurt really, but it is
> far from elegant (and error prone during debugging).
> Think of hosts with several OLSR interfaces (e.g. on antennas,
> LANs, OpenVPN endpoints).
Do you mean that Linux automatically assigns a e.g. 10/8 netmask when
you only need a /24? Yes, the easiest solution is to adjust the netmask,
so that no networks that may be around interfere.
Depending on the size of your "one-hop limit", your netmask could be
narrower, of course.
> - IMHO this is the conceptually *only* correct interface address
> configuration since OLSRD routes (conceptually) only hosts and not
> subnets (with != /32 netmask).
> So relying on some "artificial" subnet declaration looks somewhat
> "fishy" to me.
I beg to differ. The subnet declaration is not artificial at all, it is
how IP works. The subnet tells the IP stack if it should send the packet
to a router or directly on the interface. So it makes sense to advertise
that you have a route to your subnets. Of course, if you have an
uncommon network layout, using netmask /32 and setting olsrd's broadcast
address to 255.255.255.255 *can* be the best (or only) solution.
> "artificial" because it has nothing to do with routing (except that it
> defines a broadcast address. But I can configure it also in the config
> file) or broadcast or collision domains but more a pure administrative
> given value.
As I mentioned earlier, I did not completely understand what you mean,
but note that the netmasks almost only purpose *is* routing decisions.
Defining a broadcast address is almost negligible :)
>> The broadcast option is only needed when you want to connect to nodes
>> that are in your one-hop radius, but have a different network address.
> Yes, but the next hop has potentially an address from a complete
> different subnet.
That why you use olsrd in the first place. Consider this simple example:
10.0/16 ---box1--- 1.2.3/24 --- box2 ---- 5/8
Thanks to olsr you can route from 10.0/16 to 5/8, out of the box, no
configuration needed (Except telling olsrd which interface to use...)
>> A (bad) example would be an ethernet where 10.0/16 and 192.168/16
> See it as an example setup for this discussion - there are several
> reasons why such setups may make sense and they are IMHO absolutely
> unavoidable in the mid-term.
If you have good reasons for such a layout, use the -b 255.255.255.255
option. Thats why its there :)
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