[OLSR-users] Re: [olsr-dev] olsrd on multiple interfaces

Pawel Foremski (spam-protected)
Sun Sep 26 21:56:57 CEST 2004

On Sunday 26 of September 2004 19:53, Andreas T√łnnesen wrote:
> The concept of IP routing is based on the fact that one has an unique
> outgouing interface for a given IP address. If you set up multiple
> interfaces and add the same route through these this would mess up the
> whole IP routing basics. If i set up a box with two interfaces eth0 and
> eth1 and add the route 192.168.10/24 to both of them - then chances are
> that all traffic destined for that network will end up being routed
> trough the interface with the first entry in the routing table. This is
> IMO not because the routing mechanism lacks some feautre - but because
> the whole setup is bad.

Well, I know that normally each interface should have different IP address, 
but as I said sometimes it's useful to use only one IP address for one 
machine - for example just for easiness and simplicity :).

> > 1. Even if I were using all ports as switch, there is also the WiFi
> > interface - eth1, which I also need to run olsrd on.
> Are you saying that _all_ physical devices use the same IP address? The
> WLAN, eth and switch??  


> If not (...)
> > 2. I need all ports to be separated (security, flexibility, more control,
> > etc..).
> Ok - this is where you need to convince me with more arguments. Why is
> this separation of ports on a switch needed on the _routing_ layer?

I'm building a wide wireless network with Internet access. I use WRT54Gs to 
build my backbone - some of them are connected by WiFi and some by Ethernet. 
Then, I run PPPoE on some interfaces ("access" interfaces) to be sure that 
only registered users can connect. The interface(s) PPPoE is running on can't 
forward traffic - only PPP interfaces created by PPPoE sessions are allowed 
to forward.

I divided all of the interfaces available on WRT54G to "backbone" and "access" 
- "backbone" connects to WRT54Gs and "access" will have some Access Points, 
hubs or switches connected. Because some interfaces are trusted and the other 
not (especially these with "open" Access Points) I must separate them.

> >>How does you routing table look(having four devices
> >>set up within the same subnet) - and on what ports are a regular
> >>broadcast ( routed?
> >
> > All interfaces have netmask and broadcast
> > set up.
> Ok - so you've got something like
> DST           IFACE
>      vlan1
>      vlan2
>      vlan3
>      vlan4
> in your routing table?

On Sunday 26 of September 2004 21:16, Andreas T√łnnesen wrote:
> Ups... seems I overlooked the fact that your interfaces were set up with
> a netmask of Please disregard the suggestion of the
> routingtable that I gave. I guess there is no arrgegated routing done
> via these interfaces.

Yes, you're right.

> >>Are the vlan devices layer2 tagging
> >>devices(VLAN) - or just some way of accessing the individual ports?
> >
> > Well... both? :)
> Ok - are using different 802.1q tags for every port on the switch?

Yes. Practically each port is one interface.

> >>To me it seems that a routing protocol should
> >>consider the switch _one_ interface, not four.
> >
> > As I wrote - even if vlan1 to vlan4 were considered as eg. vlan0, there
> > is always eth1. And apart of that, I also can't bridge all of my
> > interfaces due to security reasons.
> I'm not saying you should bridge your interfaces.

I know :), just a word about possible work-around...

> OLSR works fine on 
> multiple interfaces if the prequesite that all interfaces use uniqe IP
> addresses is fulfilled - which I again belive is a basic of IP routing.
> The problem here is that you are using multiple interfaces configured
> with the _same_ IP address. What I am saying is that olsrd should IMO
> run on your etherneth interface(beein the "Internet port" on the WRT),
> you WLAN interface and your switch(the switch as _one_ device).

I know, I know, I know :). I'm not trying to deny any of networking 
principles. In my situation it's just the best to assign one IP address to 
the box, not to a particular interface. I noticed olsrd doesn't support it, 
wrote a patch and sent it - that's all. I don't want to explain all of my 
intentions, as this mailing list isn't about it :). I know what I'm doing and 
that it's not the "perfect way". Just thought it might be useful - if not - 
just ignore it - it's your project.

Kind regards.

Pawel Foremski

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