I have just had PPPoE DSL service installed at a remote office location. The DSL modem/router is a Motorola Netopia 3000. The DSL service has five static IP addresses: x.x.x.241-245, with .246 as the gateway, and 255.255.255.248 as the mask. The DSL service is working properly; when I connect the DSL modem to the LAN with its DHCP server enabled, it leases addresses to the clients, and they are able to browse the web, etc.
Now, I have a Cisco ASA 5505 that I would like to use for a VPN connection to the main office.
In the past, I have dealt with only T1 and Cable, not DSL. With Cable, I would simply assign one of my public IP addresses to the outside interface on the ASA, assign a LAN address (e.g. 192.168.1.1) to the inside interface, and configure a static route using the service's gateway address -- and voilà! I'm in business.
Note: In the above scenarios, I have typically used internal DHCP and DNS servers. In this case, I have no server on the LAN; I would like to use the 5505 as a DHCP server, and point my clients to the ISP DNS servers.
So, I configured the ASA as noted above, enabling the DHCP server to hand out my ISP's assigned DNS servers. When I installed the ASA between the Netopia and my LAN switch, the DHCP server on the 5505 properly assigned everything to the clients on the LAN, but I had no DNS resolution (DNS server not reachable via nslookup) -- no traffic outbound at all, even bypassing DNS.
I have heard that DSL doesn't get along very will with Cisco equipment "out of the box", but having never worked with the two in tandem before, I'm not sure where to begin troubleshooting.