When a client configured for explicit forward proxy needs to access an HTTP/HTTPS site, it first sends an HTTP CONNECT request to the configured HTTP proxy. This CONNECT request tells the proxy that TMS is asking permission to connect directly to the HTTP/HTTPS server, endpoint etc...
5. The Proxy Denied the request since you are using a browser that is not supported by one of the Proxy policies. What this means? In this scenario the proxy scans for UA (user agent ) within the header hence is getting blocked by a policy or ACL of your proxy.
From the capture the UA is not the browser is TMS, look below:
User-Agent: TMS Http User Agent (compatible; MSIE 5.5; Windows NT 5.0)\r\n
Resulting in this (TCP/403)
The Proxy may be blocking anything that is not IE Mozilla/5.0 (compatible; MSIE 10.6; Windows NT 6.1; Trident/5.0; InfoPath.2; SLCC1; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET CLR 2.0.50727) 3gpp-gba UNTRUSTED/1.0
This is one of the scenarios there is another scenario were the proxy challenge TMS for authentication resulting in the same denied 403 since TMS/server does not know what to do with a TCP response of 401/407 challenge. Basically TMS/server does not send the credentials hence the Proxy blocks the request and the results will be the same causing TMS to report "No http response" "No SNMP response" after a (TCP/403) denied.
They are 2 ways of deploying proxies 1 with and explicit connection 407 and 2 with a redirection (WCCP) 401 meaning no proxy setting requires in your browser. Basically this means the client does not know there is a proxy VS pushing all traffic to the proxy via IE, FireFox etc...
If I check the bypass proxy for local address, will it work on a transparent proxy?
How to know when TMS is being challenge by authentication from a proxy?
In WireShark filter http.response.code==401 you can see TMS is challenge by authentication 401 NOT 407. But in this scenario it will not matter because your proxy on that network is using some kind of redirection like WCCP (Web Cache Protocol) hence it will denied access.
When requests are being redirected to the Proxy transparently, the Proxy must pretend to be the destination, since the client is unaware of the existence of a proxy. On the contrary, if a request is explicitly sent to the Proxy, the Proxy will respond with it's own IP information.
There are a few differences between explicit and transparent client HTTP requests:
1. An explicit request has a destination IP address of the configured proxy. A transparent request has a destination IP address of the intended web server (DNS resolved by the client)
2. The URI for a transparent request does not contain the protocol with the host: Transparent GET / HTTP/1.1 Explicit GET http://www.google.com/ HTTP/1.1 Both will contain an HTTP Host header that specifies the DNS host
To fix this issue, I recommend the following options:
1. Creating a Policy on your Proxy that will allow any access to the inside network. 2. Creating a Policy that will allow all for TMS. 3. Creating a ACL in your router or ASA that will allow any incoming or outgoing traffic from host 172.16.107.54
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