A firewall, IDS, IPS, or other packet inspection device is blocking the WSA.įirst determine if the TCP RST is coming from the L4TM or from another device. The Cisco Layer 4 Traffic Monitor (L4TM) is blocking the WSA proxy from connecting the web server.Ģ. If the WSA receives a TCP reset packet on its upstream connection to the web server, the WSA will send a 504 Gateway Timeout error to the client.ġ. If the web server return path packets are being sent to the client instead of the WSA, the WSA will never see the servers SYN/ACK and will send a 502 Gateway Timeout error back to the client.ĥ04: The WSA is receiving a TCP reset (RST) terminating the connection with the web server. In order to use client IP spoofing, the network must be configured in a very specific way in order to facilitate that the packets are redirected properly.Without a special network setup, the return packet will be sent to the client instead of the WSA. The WSA sends the SYN, but instead, uses the client's IP as the source.When the packet comes back, it goes directly to the WSA. The WSA sends a SYN to the web server using its own IP address as the source.If explicitly proxying through the WSA or the telnet test is successful, this shows that the WSA can communicate directly to the web server, but when a client proxies through the WSA with IP spoofing, there is a problem. IP Spoofing enable, but not properly configured It is recommended that the firewall logs and/or packet captures from the firewall are analyzed for further details. If the ping is successful, but the telnet fails, there is a good possibility that a filtering device, such as a firewall, is preventing this traffic from getting through the network. See the instructions further in this article for performing a telnet test. If the ping succeeds, then we can know for sure that the WSA has a basic layer3 level of connectivity to the web server.Ī telnet test will verify if the WSA has the ability to establish a TCP connection on port 80 to the web server. It may mean that ICMP packets are getting blocked somewhere in the path. WSA> ping If the ping fails, it does not mean that the server is down. This can be done by using the following CLI command: The first step is to verify if the WSA can ICMP ping the web server. IP spoofing is enabled on the WSA, but is not properly configured (no return path redirection) A firewall or similar device is dropping either the WSA SYN packets or the web server's SYN/ACKĤ. A network issue on the WSA network is preventing the SYN packets from getting to the Internet.ģ. The web server or web server network is having issues.Ģ. ![]() If the web server does not respond to the WSA's SYN packets, after a certain amount of attempts, the client will be sent a 502 Gateway Timeout error.ġ. 504: The WSA has established a TCP connection with the web server and sent a GET request, but the WSA never receives the HTTP response.īelow are examples of each scenario and more details regarding potential issues:ĥ02: The WSA has attempted to establish a TCP connection with the web server, but has not received a SYN/ACK.504: The WSA is not getting a response from a required service prior to communicating with the web server, such as DNS is failing.504: The WSA is receiving a TCP reset (RST) terminating the connection with the web server.502: The WSA has attempted to establish a TCP connection with the web server, but has not received a SYN/ACK.Here are a few examples of the types of scenarios that may occur: Although these error responses are similar, it's important to understand the subtle differences between them. There are many reasons why WSA may return a 502 or 504 gateway timeout error. ![]() Users are receiving 502 or 504 gateway timeout errors when browsing to websites. Symptoms: Users are receiving 502 or 504 gateway timeout errors from the Cisco WSA when browsing to certain websites Why do we see 502 / 504 GATEWAY_TIMEOUT errors when browsing to certain sites?
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