Cisco 877 - Routing & NAT Issues

Unanswered Question
Jul 6th, 2007

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.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Panther256 Fri, 07/06/2007 - 16:06

You may disregard this message... Unless you want to check over the config and make comments. It turns out that we stopped using DHCP when we switched to the 877 and we did not add the WINS server to our workstations. I believe this may have been the first issue. The second issue is isolated to a specific remote machine and we are planning on analysing their router and checking with their ISP before looking at the 877.

Thanks all

Panther256 Fri, 07/06/2007 - 18:49


ok, the resolution problem persists. When I ping my internal email server by doiman.ext it does not resolve to the inside server's IP address. Instead it is resolving to the external IP of the 877 and dying there. Any ideas? I believe the 877 is set to the interior DNS servers but I did notice that the externals are listed as well...


This Discussion