Fiddler not capturing WCF traffic from the web server to the application server - fiddler

Question

I have two possible flows:
ConsoleClient -(1)-> ApplicationServer
or
SilverlightClient -(2)-> WebServer -(3)-> ApplicationServer
Fiddler successfully captures the HTTP traffic on the (1) and the (2), but not on the (3). Here is a sample capture on (1):
POST /WcfDemo/ws HTTP/1.1
Content-Type: application/soap+xml; charset=utf-8
Host: il-mark-lt
Content-Length: 521
Expect: 100-continue
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing"><s:Header><a:Action s:mustUnderstand="1">http://tempuri.org/IWcfDemoService/Add</a:Action><a:MessageID>urn:uuid:d7fde351-12fd-4872-bc26-52ff97f126e9</a:MessageID><a:ReplyTo><a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address></a:ReplyTo><a:To s:mustUnderstand="1">http://il-mark-lt/WcfDemo/ws</a:To></s:Header><s:Body><Add xmlns="http://tempuri.org/"><x>4</x><y>5</y></Add></s:Body></s:Envelope>
HTTP/1.1 200 OK
Content-Length: 399
Content-Type: application/soap+xml; charset=utf-8
Server: Microsoft-HTTPAPI/2.0
Date: Sat, 17 Sep 2011 20:57:16 GMT
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing"><s:Header><a:Action s:mustUnderstand="1">http://tempuri.org/IWcfDemoService/AddResponse</a:Action><a:RelatesTo>urn:uuid:d7fde351-12fd-4872-bc26-52ff97f126e9</a:RelatesTo></s:Header><s:Body><AddResponse xmlns="http://tempuri.org/"><AddResult>9</AddResult></AddResponse></s:Body></s:Envelope>
And here is an example of (2):
POST /WcfDemoService.svc/ws HTTP/1.1
Host: localhost:56970
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0.2) Gecko/20100101 Firefox/6.0.2
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8,application/json
Accept-Language: fr-FR,fr;q=0.9,en-US;q=0.8,en;q=0.6,he-IL;q=0.5,he;q=0.4,ru-RU;q=0.3,ru;q=0.1
Accept-Encoding: gzip, deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Connection: keep-alive
Referer: http://localhost:56970/ClientBin/SilverlightClient.xap
Content-Length: 581
Content-Type: application/soap+xml; charset=utf-8
<s:Envelope xmlns:a="http://www.w3.org/2005/08/addressing" xmlns:s="http://www.w3.org/2003/05/soap-envelope"><s:Header><a:Action s:mustUnderstand="1">http://tempuri.org/IWcfDemoService2/Add</a:Action><a:MessageID>urn:uuid:e8420d3e-f568-49ce-bfc7-5631d5bf3fd0</a:MessageID><a:ReplyTo><a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address></a:ReplyTo><a:To s:mustUnderstand="1">http://localhost:56970/WcfDemoService.svc/ws</a:To></s:Header><s:Body><Add xmlns="http://tempuri.org/"><x>11</x><y>22</y><serverChannelKind>ws</serverChannelKind></Add></s:Body></s:Envelope>
HTTP/1.1 200 OK
Server: ASP.NET Development Server/10.0.0.0
Date: Sat, 17 Sep 2011 20:59:23 GMT
X-AspNet-Version: 4.0.30319
Content-Length: 401
Cache-Control: private
Content-Type: application/soap+xml; charset=utf-8
Connection: Close
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing"><s:Header><a:Action s:mustUnderstand="1">http://tempuri.org/IWcfDemoService2/AddResponse</a:Action><a:RelatesTo>urn:uuid:e8420d3e-f568-49ce-bfc7-5631d5bf3fd0</a:RelatesTo></s:Header><s:Body><AddResponse xmlns="http://tempuri.org/"><AddResult>33</AddResult></AddResponse></s:Body></s:Envelope>
Now, I am absolutely sure the (3) does get through. So, it all boils down to some misconfiguration on the WebServer, but I cannot nail it. The Web server is just a trivial ASP.NET application hosted within IIS. It even has the following lines in the web.config:
<system.net>
<defaultProxy>
<proxy bypassonlocal="false" usesystemdefault="true" />
</defaultProxy>
</system.net>
Still, this does not work.
To further strengthen my suspicion on the web server configuration, I have checked the SilverlightClient --> ApplicationServer flow and it is captured just fine.
I am using the Asp.Net development server.
Edit
Running procmon reveals that the following suspicious registry key is consulted (amongst others):
HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\ProxyBypass
And on my machine it was set to 1. I have changed it to 0 and seems like it solved my issue. The only problem is that when I change it back to 1 Fiddler continues to capture the problematic leg! Very interesting.
Anyway, I am satisfied, for now.

Answer 1

You are calling "localhost" right?
Fiddler is not able to capture the local traffic if you are using "localhost" as hostname.
Solutions:
Use servername (e.g. myserver)
Use ip4.fiddler (e.g. http://ipv4.fiddler:8787)

Answer 2

Not sure if these are causing it ... but,
A few things to check:
In IIS7 the appPool has a loadUserProfile setting. It causes the session to load a user profile which means it can get system proxy settings.
Check the code making the request from the webServer - even if you configure to use the system proxy and bypass onLocal (which only applies to names without dots in it), code making the request can still explicitly set to use or not to use a proxy.
Far fetched but you may want to play with the account the appPool runs as - local account with profile vs. Network Service.
Hope that helps - these network things have a lot of variables between two points :)