Yes, you still do not know whether the firewall or the server is the problem, but you can at least rule out basic networking problems being the cause. If that succeeds, you at least know that the host is up and responding to network traffic. For example, if the server in question is not only the web server but is also the ftp server, attempt to establish an FTP connection to the server. Another option is to attempt to access the server using a different, but permitted, protocol. If you can, it is a good bet that the problem has to do with the application itself, not the firewall. Doing so allows you to verify the fundamental ability to access the web server. For example, if you are having difficulties accessing a website that is being protected by a firewall, a good idea to verify connectivity is to just attempt to telnet to TCP port 80.
There is one warning firewall is not functioning correctly how to#
In these situations, it is important to understand the nature of the application or resource that is being troubleshot and to think outside the box in terms of how to test connectivity.
Consequently, trying to use tools and utilities such as PING and traceroute to verify connectivity can be difficult if not impossible to do. In most cases, this means that traffic such as ICMP traffic is going to be blocked by the firewall. The reason for this is simple: To protect the host, configure the firewall to provide the minimum required protocols and services necessary to allow access to the protected resource. Testing connectivity for traffic passing through the firewall is easier said than done, particularly when troubleshooting traffic destined for a protected host from an unprotected network. In most cases, it never dawns on them that the application itself may be experiencing problems (for example, if the server is down or the application itself is misconfigured). Many times, all they know is that the traffic goes through the firewall (and therefore the firewall must be the cause of the problem). In troubleshooting traffic through the firewall, this is particularly important because in most cases the user or technician reporting the problem likely has a limited understanding of what role the firewall plays in the communication process with the host on the other side of the firewall. The first step of troubleshooting is to always verify that the problem being reported is the problem that is occurring, and not merely a symptom of the problem. Review the firewall translation configuration.Īlthough these steps may seem to be many of the same steps as previously discussed, it is important to consider the context of the problem, namely passing traffic through the firewall, as you apply each step in the checklist. Verify that the remote application is running and accessible locally. This section covers each step from the flowchart in turn as follows: Troubleshooting Connectivity Through the Firewall The troubleshooting connectivity through the firewall flowchart is based on the general troubleshooting checklist but has been modified for this specific situation.įigure 13-2. A good approach to troubleshooting connectivity through the firewall is to use the flowchart in Figure 13-2.
There are any number of reasons for this, but the most common reasons involve problems with the firewall ruleset, problems with the firewall translation tables, problems with Network Address Translation (NAT), or problems with how the application communicates over the network.
No matter how well planned, tested, and implemented, sooner or later you will run into problems accessing resources through the firewall.
To assist in troubleshooting these situations, implement your firewall troubleshooting checklist as it applies to the scenario in question. Understanding this, you can further narrow down the process to two things: Three predominant situations with firewalls require some form of troubleshooting:Īccess to protected resources from unprotected networks is not functioning correctly.Īccess to unprotected resources from protected networks is not functioning correctly.Īccess to the firewall itself is not functioning correctly.
0 kommentar(er)
