[B.A.T.M.A.N.] problem starting batmand (v799)

[B.A.T.M.A.N.] problem starting batmand (v799)

[Sebastian Hagen]

Hello *,

I'm the author of the mipip olsrd patch mentioned by rene. The olsrd code
was very close to doing the Right Thing (see below), my patch just fixed a
few minor internal API issues that prevented it from working out correctly.

I haven't seriously looked at the b.a.t.m.a.n. code, so I don't know exactly
why it's causing problems for rene.

Axel Neumann wrote:
> IMO that does only work if the interfaces of a node are NOT connected to the 
> same physical/logical link (e.g. B1 and B2 are operating on different 
> channels or with different cell IDs,...). Otherwise specifying the outgoing 
> interface is not enough. Even if node A has only one interface (A1). If there 
> is a link A1<->B1 and a link A1<->B2 the problem remains:
>> > How could it set up the routing table to ensure that a packet
>> > to a distant node C should be routed via B1 (and NOT via B2)?
> The outgoing interface of node A is A1, for both cases. Setting the outgoing 
> interface to A1 has no effect. 
> 
> Maybe there is a way to configure the next-hop-mac address instead of the 
> next-hop-ip address. But then you rather have layer 2 routing and not layer 
> 3.
This is an interesting case. You're correct that in this configuration, a l3
routing daemon on A can't make a deliberate choice of which interface of B
to send data to. This is obviously suboptimal, and should be avoided.

However, there are plenty of cases where this will predictably not occur.
For instance, in the opennet mesh network in Rostock, we have quite a lot of
nodes which have one wired interface and one wireless interface, both of
which are used for communication with other nodes in the mesh cloud.
Assigning separate IP addresses to the different interfaces on those nodes
would be wasteful of our address space.

Imo, the choice whether to assign different IP addresses to the different
interfaces on a specific meshnode should ideally lie with the (hopefully
competent) network admins, and routing daemons should decently support
either configuration, with the implicit understanding that having different
interfaces a) in the same broadcast domain AND b) with the same IP addresses
may lead to silent performance degradation.
That's what the newer versions of olsrd do.

Regards,
Sebastian Hagen

[B.A.T.M.A.N.] problem starting batmand (v799)

[rene]

Hi,

starting batmand, the daemon sometimes doesn't seem to recognize the
network the right way.


root@25:~# killall batmand
root@25:~# batmand eth1:1 vlan0:1
Using interface eth1:1 with address 192.168.42.25 and broadcast address
192.168.43.255
Using interface vlan0:1 with address 192.168.42.25 and broadcast address
192.168.43.255
-------------------------------------------------------
 This is a tcpdump from a neighbor node:

root@ap14:~# tcpdump -i eth0 src 192.168.42.25
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
05:12:09.512310 arp who-has 192.168.43.255 tell 192.168.42.25
05:12:10.512178 arp who-has 192.168.43.255 tell 192.168.42.25
05:12:11.699795 arp who-has 192.168.43.255 tell 192.168.42.25

-------------------------------------------
on the other node:
root@25:~# killall batmand
root@25:~# batmand eth1:1 vlan0:1
Using interface eth1:1 with address 192.168.42.25 and broadcast address
192.168.43.255
Using interface vlan0:1 with address 192.168.42.25 and broadcast address
192.168.43.255
root@25:~#

----------------------------------------------
tcpdump:

05:12:28.621940 IP 192.168.42.25.4305 > 192.168.43.255.4305: UDP, length 20
05:12:28.873246 IP 192.168.42.25.4305 > 192.168.43.255.4305: UDP, length 25
05:12:28.892343 IP 192.168.42.25.4305 > 192.168.43.255.4305: UDP, length 15


now batmand is running successfully.

Any Ideas?

regards,
Rene

Re: [B.A.T.M.A.N.] problem starting batmand (v799)

[Axel Neumann]

Hi,

On Dienstag 20 November 2007, rene wrote:
> Hi,
>
> starting batmand, the daemon sometimes doesn't seem to recognize the
> network the right way.
>
>
> root@25:~# killall batmand
> root@25:~# batmand eth1:1 vlan0:1
> Using interface eth1:1 with address 192.168.42.25 and broadcast address
> 192.168.43.255
> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
> 192.168.43.255

> -------------------------------------------
> on the other node:
> root@25:~# killall batmand
> root@25:~# batmand eth1:1 vlan0:1
> Using interface eth1:1 with address 192.168.42.25 and broadcast address
> 192.168.43.255
> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
> 192.168.43.255
> root@25:~#
>

What is definitively not correct is that your capture indicates 4 times the 
same IP address (192.168.42.25) on 4 different interfaces. 
Can you check whether your capture, the alias-interface configuration (what is 
the output of ip a ?), or the daemon is wrong?
There MUST be a different IP address for each BATMAN interface in the network 
(also if a single BATMAN node has more than one interface). 
All BATMAN interfaces SHOULD  have the same netmask and broadcast address.

ciao,
axel

Re: [B.A.T.M.A.N.] problem starting batmand (v799)

[rene]

Hi,

Axel Neumann wrote:
> Hi,
> 
> On Dienstag 20 November 2007, rene wrote:
>> Hi,
>>
>> starting batmand, the daemon sometimes doesn't seem to recognize the
>> network the right way.
>>
>>
>> root@25:~# killall batmand
>> root@25:~# batmand eth1:1 vlan0:1
>> Using interface eth1:1 with address 192.168.42.25 and broadcast address
>> 192.168.43.255
>> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
>> 192.168.43.255
> 
>> -------------------------------------------
>> on the other node:
>> root@25:~# killall batmand
>> root@25:~# batmand eth1:1 vlan0:1
>> Using interface eth1:1 with address 192.168.42.25 and broadcast address
>> 192.168.43.255
>> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
>> 192.168.43.255
>> root@25:~#
>>
> 
> What is definitively not correct is that your capture indicates 4 times the 
> same IP address (192.168.42.25) on 4 different interfaces. 
This is two times the same node, first time it recognizes the broadcast
the right way, second time not.

> There MUST be a different IP address for each BATMAN interface in the network 
> (also if a single BATMAN node has more than one interface). 
Is this implemented like this (where?)? Can't work BATMAN with the
interfaces (or can't we change it to work this way), it would make the
whole configuration much easier to assign to every node only one single
IP address (or two, one for olsr and ne for BATMAN)? We are doing this
with olsr and this really makes the network-structure much cleaner -
every node has one IP.

Is the described problem with the misconfigured broadcast related to the
'same IP on different interfaces' issue?

regards,
Rene

Re: [B.A.T.M.A.N.] problem starting batmand (v799)

[Axel Neumann]

Hello,

On Dienstag 20 November 2007, rene wrote:
> Hi,
>
> Axel Neumann wrote:
> > Hi,
> >
> > On Dienstag 20 November 2007, rene wrote:
> >> Hi,
> >>
> >> starting batmand, the daemon sometimes doesn't seem to recognize the
> >> network the right way.
> >>
> >>
> >> root@25:~# killall batmand
> >> root@25:~# batmand eth1:1 vlan0:1
> >> Using interface eth1:1 with address 192.168.42.25 and broadcast address
> >> 192.168.43.255
> >> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
> >> 192.168.43.255
> >>
> >> -------------------------------------------
> >> on the other node:
> >> root@25:~# killall batmand
> >> root@25:~# batmand eth1:1 vlan0:1
> >> Using interface eth1:1 with address 192.168.42.25 and broadcast address
> >> 192.168.43.255
> >> Using interface vlan0:1 with address 192.168.42.25 and broadcast address
> >> 192.168.43.255
> >> root@25:~#
> >
> > What is definitively not correct is that your capture indicates 4 times
> > the same IP address (192.168.42.25) on 4 different interfaces.
>
> This is two times the same node, first time it recognizes the broadcast
> the right way, second time not.
of course, ive been somwhow distracted by "the other node"
>
> > There MUST be a different IP address for each BATMAN interface in the
> > network (also if a single BATMAN node has more than one interface).
>
> Is this implemented like this (where?)? 
Yes it is implemented/designed like this. It operates on layer three and 
above. IP addresses are used to differentiate between different links to the 
same neighbors. For example two nodes A and B, each with two wireless 
interfaces 1 and 2. All interfaces operating in the same channel, bssid, ...
How could node A differentiate between the link A1<->B1 and A1<->B2 if it is 
not aware of any MAC addresses. But even if it is aware of MAC addresses. How 
could it set up the routing table to ensure that a packet to a distant node C 
should be routed via B1 (and NOT via B2)?
 
> Can't work BATMAN with the 
> interfaces (or can't we change it to work this way)
i guess its not that easy but if you are familiar with protocol design and c 
coding go ahead...
Or you take a look on batman-advanced, but thats another story :-)
> , it would make the 
> whole configuration much easier to assign to every node only one single
> IP address (or two, one for olsr and ne for BATMAN)? We are doing this
> with olsr and this really makes the network-structure much cleaner -
> every node has one IP.

Actually, I did not even know that this is possible - is such a configuration 
proposed somewhere. I can imagine that this somehow works but how shure are 
you that this does not introduce any negative side effects?

ciao, 
axel

>
> Is the described problem with the misconfigured broadcast related to the
> 'same IP on different interfaces' issue?
>
> regards,
> Rene
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