I have 2x cisco routers connected back to back with an ethernet connection to my cable modem. The router connected to my cable modem is configured with irb and setup as a transparent IPS. The second router is configured with the new cbac zone based firewall which then connects to my Private network.
The setup works fine for a number of days then I find I cannot connect to the internet. When I look at the router connected to my LAN it has no ip address. With debugging I can see the DHCP requests but I am getting no replies. If I plug my cable modem directly into my first router (bypassing the irb router) it gets an address no problem. I can then reconnect the irb router and it works fine again for a period of time.
When its in the failed state I see the arp table on the irb router shows my public IP address as incomplete and debugging on my first router shows no UDP packets recieved yet I see plenty on the IRB router.
Does anyone know what the problem is or how I can look at the mac addresses in the UDP packets? Is there any other tables I should be looking at?