I'm trying to understand the logic behind the failure in the following scenario:
a. If a linux bridge with 2 interfaces, eth0 (LAN) and eth1 (WAN) is behind an ISP device e.g. a cable modem, it does not receive an ip address even if the bridge interface (br0) is set to do so. Instead, it forwards the DHCP offer to the device behind the bridge i.e. whatever device is connected to eth0.
dhclient br0 indicates that no leases get offered at all and dhclient then goes back to the leases recorded in dhclient.leases, which are old and irrelevant.
b. if the bridge is inside the LAN itself with eth1 being exposed to an internal DHCP server, it does retrieve an ip address. And so do the devices behind it.
The /etc/network/interfaces contains:
auto lo eth0 eth1 br0 iface eth0 inet dhcp iface eth1 inet dhcp iface br0 inet dhcp bridge_ports eth0 eth1 bridge_stp off
- This is puzzling. Any idea why this is happening? What's different in b vs. a?
- Is there a way to force br0 to obtain an ip address first and not pass it downstream?