Hi,

We are trying to use some openwrt boxes (one Linksys WRT54GL, one RouterBoard150, both MIPS) on a network with heavy(?) IP multicast traffic.
The network is a 100Mbps switched ethernet, and there's a constant multicast traffic of about 10Mpbs. The IP multicast traffic appears as Ethernet broadcast.
The openwrt boxes should not receive multicast, so I have turned IP_MULTICAST off in their kernel.

Once connected to the network, the openwrt boxes become extremely slow, and I can see about 50-60% "softirq" with top.
(For now, there's nothing running on them just a dropbear server).
Again, the boxes should not receive the multicast, it is just "present" on the network.

If I decrease the amount of multicast (experimentally), the softirq loads go down as well, and once below cca. 20%, the boxes become responsive again. The 2 boxes behave the same way.

Questions:

1. Is this normal ? Why ? I assume the kernel should immediately drop all broadcast pkts (or not receive them at all).
2. Is there anything else to configure about this ?
3. What is "high" and why ? What bandwidth of "coexistent" multicast traffic is too high for such a box ? PCs and other devices (e.g. IPTV SetTopBoxes with similar HW) seem to have no problems on this network.

thanks,
Tivadar