Here is a text version of /etc/services that might be useful for determining whether a port is being used by a trojan, etc: TCP and UDP Service Listing

There is some apparent voodoo on what, exactly, is needed to add an IP address to an interface using Red Hat style scripts. We have tested this on Red Hat Enterprise 3 and CentOS 4, and it appears that the convention is quite forgiving. This makes sense, really, since if you hose up these interfaces, […]

If you wish to bring up a Cisco router that has an IP address that conflicts with existing hosts on your network, there are a variety of ways to change it. We just happened to have a crossover network cable sitting on our work bench, and a GNU/Linux host on the LAN with an extra […]

Nmap can be used to fingerprint operating systems. Here is a typical session: [root@srv-1 usr-1]# nmap -O –min_rtt_timeout=6000 10.50.100.1-80 Starting nmap 3.70 ( http://www.insecure.org/nmap/ ) at 2006-05-05 12:49 PDT Interesting ports on 10.50.100.1: (The 1656 ports scanned but not shown below are in state: closed) PORT STATE SERVICE 22/tcp open ssh 111/tcp open rpcbind 6000/tcp […]

There is a limit on the number of concurrent socket connections that an application can accept in BSD, Windows, and other operating systems. This is set at compile time, but it can be overridden. Here is a discussion of this limitation by Microsoft, and here is further discussion. One application that is sticking this on […]

There is a cool option on some versions of ping. With the -f option, a dot is printed for each ping sent, and a backspace is printed when a ping is received. This gives you an instant visualization of the lost packets. Hit ctrl-c to end the task, and you will then see the latency […]

We wrote up a tool that will generate a latency and trace report based on your IP address. Note that this is the IP address that the web server detects your client has. First it pings your IP address with 50 pings or 5 seconds worth of pings, whatever is the most restrictive. If 50 […]

In this article we will show how to monitor network health from the client perspective using our AreWeDown tool. We will then disrupt communication from the client perspective to the server by using a ping flood, and will solve the problem using traffic shaping. Let’s start out with a healthy network: | 2005-08-06 08:13:50 | […]

Here is our subnet reference guide and The Perl script used to generate it If you want an easy to use subnetting calculator, Subnet-Calculator.org is one of the best ones we’ve seen online. Subnet Reference Guide — Value of individual bits in an eight bit byte if true: Bit 7 = 128 Bit 6 = […]

If you have a WAN, then one very important concern should be latency. Latency, in this case, is the time that a package of information takes to reach the other end of the slow link. This package of information could be a DNS query, ping, file, or a transaction in a client/server application. Notice that […]