While using the linux bridge module in 2.6.10, the kernel seems to munge the source IP address of broadcast UDP packets if they come from "0.0.0.1", and sticks on an address of the linux host. I humbly submit that re-writing the source address of packets is not proper behavior for a bridge, even if those source addresses are not traditionally valid. Sure, 0.0.0.1 isn't a valid address, but it's used by the XBOX games for "System Link" play. See http://caia.swin.edu.au/genius/020802A/ for more details, but basically XBOXes talk to each other by sending UDP port 3074 packets with 0.0.0.1 as the source address. When searching for other XBOX systems, these are broadcast packets addressed to 255.255.255.255/ff:ff:ff:ff:ff:ff. So I was trying to get two XBOXes to talk to each other through a Linux machine configured as a bridge, (mostly so I could watch the traffic) and it didn't work. Here's what tcpdump saw: $ sudo brctl show br0 bridge name bridge id STP enabled interfaces br0 8000.00112f9de921 yes eth0 eth2 $ sudo tcpdump -n -e -i eth0 port 3074 tcpdump: WARNING: eth0: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 19:28:27.715755 00:50:f2:f1:fb:07 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 102: IP 0.0.0.1.3074 > 255.255.255.255.3074: UDP, length: 60 ### line above appears to be xbox 1 broadcasting to find other hosts 19:28:28.772223 00:50:f2:ba:39:89 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 102: IP 66.92.162.116.3074 > 255.255.255.255.3074: UDP, length: 60 ### line above is linux bridge forwarding packet from xbox 2, I think. Note IP address is of linux box, not 0.0.0.1 $ sudo tcpdump -n -e -i eth2 port 3074 tcpdump: WARNING: eth2: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth2, link-type EN10MB (Ethernet), capture size 96 bytes 19:28:27.715816 00:50:f2:f1:fb:07 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 102: IP 66.92.162.116.3074 > 255.255.255.255.3074: UDP, length: 60 ### line above is linux bridge forwarding packet from xbox 1. Note IP address is of linux box, not 0.0.0.1 19:28:28.772135 00:50:f2:ba:39:89 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 102: IP 0.0.0.1.3074 > 255.255.255.255.3074: UDP, length: 60 ### line above is xbox 2 broadcasting to find other hosts
