Error: Network error (tcp_error) when browsing the Internet; 503 error returned

Solutions ID:    KB1215
Version:    4.0
Status:    Published
Published date:    03/02/2009
Updated:    03/07/2012

Problem Description

Error: Network error (tcp_error) when browsing the Internet
You get a Network error (tcp_error) when browsing the Internet

You get: Request could not be handled when browsing the internet.
In a packet capture you see a 503 error returned by the proxy to the client.


There are many reasons a Network Error (tcp_error) is returned from the ProxySG. Below are several examples that Blue Coat Technical Support has encountered.

For a new implementation or topology change, the IP gateway may be misconfigured, there may be a Layer 2 / 3 loop on the network, asymmetric routing or something upstream is not passing the proxy's traffic to the Internet.

Consult your Blue Coat Sales Engineer or Reseller if this is a new implementation or any topology change that affects traffic flow to or from the ProxySG.

If the problem occurs with a specific URL/destination, it may be due to one of the following:

  • 3-way TCP handshake fails between the Proxy and the origin content server (OCS)
  • A reset (RST) packet coming from upstream towards the proxy on a specific tcp session
  • Something upstream is not passing the proxy's traffic out to the Internet
  • Layer 2 / 3 loop on the network for a specific URL/destination

Please obtain a packet capture when the problem occurs.  It is very important to see what is happening on the wire. You can take packet capture from the proxy by going to the URL below:


A packet capture taken from a ProxySG can be viewed by Wireshark (

Rate this Page

Please take a moment to complete this form to help us better serve you.

Did this document help answer your question?
If you are finished providing feedback, please click the RATE CONTENT button. Otherwise, please add more detail in the following text box and then click RATE CONTENT.

Your response will be used to improve our document content.

Ask a Question