I recently upgraded a venerable Cisco 678 to a Cisco 877 for my POTS ADSL. I have setup a basic configuration as closely to what the 678 had using the 877. Since switching there have been some strange routing issues that have affected all systems on my internal network and one issue that affects external access:
Internally I have one Cisco baseline switch and all workstations and servers plug directly into it, including the 877. The 877 is configured as the default gateway on all systems (the same way it was configured when the 678 was in service). I have a single Web server and a single DC. Both servers are running DNS for the internal network. Intermittantly when I try to use a network name, I get resolved to the external address of the 877. I have had to hardcode network addresses into the WIndows HOSTS file to keep the network operating. Am I missing a vital command to allow the 877 to ignore or bounce back internal network traffic?
The second issue is with NAT. We have configured NAT entries for our POP and SMTP server. The POP NAT works fine... The SMTP does not (on the default port). I added a high port and mapped it to 25 and got it to work. Have I done something wrong or missed a step with SMTP and NAT?
I had the firewall on for a few days but turned it off while troubleshooting these issues. Any help would be greatly appreciated. Thanks. Attached is my current configuration.