Not sure if this is a kernel issue (might be Buildroot ?), but it seems quite fundamental, so here goes:-
On our embedded Linux platform (roughly based on the NGW100 dev kit), we have 2 ethernet ports (eth0 and eth1). These are configured (via /etc/network/interfaces) as follows:-
auto lo eth0 eth1 iface lo inet loopback iface eth0 inet static address 10.0.101.2 netmask 255.255.0.0 gateway 10.0.0.1 iface eth1 inet static address 169.254.9.1 netmask 255.255.0.0 gateway 169.254.0.1
If I connect a cable *only* to eth0, from within the unit I can ping the router (10.0.0.1) and I can't ping anything on the 169.254 subnet, as I would expect (since there's no cable connected to eth1).
*BUT* from my PC (running Ubuntu), I can ping the embedded unit on either 10.0.101.2 *or* 169.254.9.1, !?!?!?!
Surely I shouldn't be able to do that ?
Using wireshark, I can see that the ping to the 169.254 address is getting replies from eth0, since the mac address in the ping reply packet matches eth0.
Here's the routing table, if that helps.
# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 169.254.0.1 0.0.0.0 UG 0 0 0 eth1 0.0.0.0 10.0.0.1 0.0.0.0 UG 0 0 0 eth0 10.0.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
If I change the eth1 ip to (say) 188.8.131.52, then the crossover ping stops.
Can you shed any light on this ?
Is it something to do with the magic "169.254" local ip address range ?