lenny: multicast not working?

[ctoo]

An observation on Bubba Server with the lenny image:

If I do the following on my laptop after some idle time:

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getent hosts bubba.local

I'm unable to resolve the IP address of my Bubba server.

Now, if I then jump to a remote shell on Bubba Server with the lenny image and do the following:

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avahi-browse -vrta

then all of a sudden I can resolve the IP address of my Bubba server from my laptop. Most likely because the avahi-browse command fills up the avahi cache on my laptop.

To investigate the issue further, I used wireshark on my laptop and tshark on bubba to monitor the network traffic at both ends. It seems that mDNS is not working because Bubba doesn't receive any multicast packets, even though ifconfig clearly states that eth0 has multicast enabled. I think I've seen similar problems reported for Bubba TWO and that this issue was being investigated by the excito developers? Is this correct.

Any ideas?

[ctoo]

Update on this. I saw that, in some cases, multicast packets did go through my router, so I didn't expect it to be the problem.

Now, just to be sure, I've tried two different settings for the routers handling of multicast (it's a Linksys WRT610N). There is actually a surprising effect (relative to what I had expected) of this setting: If I keep the "Filter Multicast" option unchecked, I am able to ping 224.0.0.2. If I set the "Filter Multicast" option checked, I can no longer ping 224.0.0.2. I actually expected that this setting only affected traffic from the WAN to the LAN and not traffic internally on the LAN.

In any case, that's a Linksys problem. The behaviour of Bubba is, however, the same - irrespective of the "Filter Multicast" setting on the router.

I've then tried to do

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ifconfig eth0 allmulti

and this did the trick!

Now, before issuing the above command, eth0 already had the MULTICAST flag set. As far as I've understood, the semanthics of the ALLMULTI and MULTICAST flags are as follows:

MULTICAST: When set, this ensures that the interface is able to send and receive multicast packets for multicast groups that the network node has joined.

ALLMULTI: When set, the network interface will receive all multicast packets - also those that the network has not joined.

It is then surprising to me that the ALLMULTI flag also needs to be set. I must admit, however, that I've also found several indications that the above is not the only interpretation of the two flags.

Does anyone know what the situation is?

[ctoo]

For those interested: A good place to ensure that ALLMULTI is set on eth0 could be /etc/network/interfaces. Here's mine:

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auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
   pre-up ifconfig eth0 allmulti
   address 192.168.1.33
   netmask 255.255.255.0
   gateway 192.168.1.1

NOTE: I haven't tested how this interacts with backend.pl of the Bubba WEB interface - I'm not sure such manual changes will survive if the network configuration is changed through the Bubba WEB interface.