Weird Cisco / Port 80 Web Site Access Issue

Fairly simple configuration, Westell DSL modem, and Cisco 1811W integrated services router configured with BVI interface and Dialer0 interface for DSL connection.

As of last night, did some DSL modem troubleshooting (changed DSL modem from "router" mode to "bridged ethernet" mode), and now client can browse any web site on the internet EXCEPT for Yahoo, and their web site hosted by Yahoo.

On the client PC I can telnet to Port 80 on and get a connection, and in Internet Explorer, for a split second, displays the page title in the title bar of the browser, then suddenly stops and displays "Cannot find server or DNS error".

This makes absolutely no sense to me. Suggestions? Urgent. :(
Who is Participating?
rpone605Connect With a Mentor Commented:
You might want to check the MTU settings on both the cisco and westel devices.
crawforditsConnect With a Mentor Commented:
Review the hosts file located in c:\windows\system32\drivers\etc.  Should look like this:

# Copyright (c) 1993-1999 Microsoft Corp.
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
# For example:
#          # source server
#              # x client host       localhost
Yves AccadConnect With a Mentor Network Security EngineerCommented:
Does this happen on all local machines?
Does it only happen in IE?
Please for testing purpouses, install firefox:
Do you have the same issues with firefox?
BrandonPotterAuthor Commented:
OK, tried all of the above comments, and stumbled upon the solution:

Apparently somewhere in the process of establishing the Dialer0 interface through Switch Device Manager, the "Inspect nonstandard HTTP traffic" was checked, with a policy action of "Drop".

Cleared this and all was well. However, unchecked "Inspect HTTPS traffic" and then HTTPS did not work at all. Weird, just checked it back and HTTPS is not blocked anymore.

Interesting Cisco animal, the 1811W + SDM.
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