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

[Andreas Tønnesen]

Hi,

Comments inline.

>>The patch looks ok(at first glance) and I can implement something
>>similar for 0.4.8... However - this sounds like a strange setup to me -
>>multiple devices using the _same_ IP address sounds like something that
>>would mess up your regular IPv4 routing if these devices are not just
>>something available to the upper layers.
> 
> 
> Why? Sometimes such setup is needed - why to limit olsrd usability only to 
> interfaces with different IP addresses? I'm currently running the patched 
> olsrd on 3 boxes which have multiple interfaces with one IP and it doesn't 
> break anything - just works.
> 

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.

>>Can't 
>>the switch device be accessed as one interface since all ports are using
>>the same address?
> 
> 
> 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 - the problem has no meaning concerning 
the WLAN and ethernet interface - only conserning the ports on the 
switch. you can run olsrd on eth0, wlan0 and sw0 just fine.

> 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?

> 
> 
>>How does you routing table look(having four devices 
>>set up within the same subnet) - and on what ports are a regular
>>broadcast (10.2.255.255) routed?
> 
> 
> All interfaces have netmask 255.255.255.255 and broadcast 10.255.255.255 set 
> up.
> 

Ok - so you've got something like

DST           IFACE
10.2.0.0      vlan1
10.2.0.0      vlan2
10.2.0.0      vlan3
10.2.0.0      vlan4

in your routing table?

> 
>>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?

> 
>>Does 
>>the patch fix your problems(the sockets bind ok to the vlan devices?).
> 
> 
> Yes, it does completely. There was no problem (in stock version) in binding on 
> multiple interfaces, only in adding a discovered route "on wrong 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. 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'm not saying that what you are suggesting is not a way of doing things 
- and I'm not arguing just to yank you chain :-) But the fact is that I 
do not agree that the port devices set up should count as devices for 
layer 3 routing. A switch is a device that should be seen as a single 
device by layer 3 mechanisms AFAICS, and the seperation of the ports on 
that switch should be done by layer 2 mechanisms.
But then again - I can be convinced othervice :-) I'm CCing this to the 
users list as well since there are more subscribers there and maybe 
others has some optinions on this.


regards,
Andreas