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

<< Back to Knowledge Search



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 (

Additional Information
Bug Number
InQuira Doc IdKB1215

Article Feedback

Hide Properties
First Published      10/01/2014
Last Modified      10/01/2014
Last Published      10/01/2014
Article Audience
Product      ProxySG
Topic      Content Access, Debugging, Errors / Event Logs / Alerts, Networking
Article Number      000016907
Was this helpful?
Previous MonthNext Month