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 […]

Here is a diagram of three servers: What we want to do is create a tunnel with SSH so that 10.50.101.100 can go directly to 10.50.100.72. There is no routing between the networks. The box in between is dual-homed and acting as a security buffer between the 10.50.100 and 10.50.101 networks. After we set up […]

In this story we showed how to upgrade IOS on a Cisco using a TFTP server available from Cisco that ran on Windows. Well, just suppose you wanted to load a new IOS image from a TFTP server on a GNU/Linux box. We will use Red Hat 8.0 to provide a TFTP server. First, install […]

Check out floppyfw for a simple firewall and IP sharing device. No hard drive is needed, and 16 megs of RAM is more than enough. The instructions on the site and in the comments in the config files are quite easy to follow. One somewhat tricky problem is if you are using a network card […]

HTTP: RFC 2068 POP3: RFC 1725 SMTP: RFC 821 FTP: RFC 959

Network Probe is a free network monitor and protocol analyzer that runs on Windows NT/2K/XP, Linux, FreeBSD, Solaris (Intel), and Mac OS X. We downloaded the Linux version by filling out the form here. The form wasn’t too intrusive, and the email with the download information came back quickly. We used version 0.4 for this […]

Network load balancing is a service that comes with Windows 2000 Advanced Server (not plain old Windows 2000). In this article we will set up Network Load Balancing on a cluster of two systems and test via the telnet service. The Network Load Balancing service is unlike other popular load balancing schemes like Red Hat […]

In order to use the WLBS CLI, you need to enable remote control: The WLBS CLI lives as wlbs.exe in system32. Query the cluster: C:\>wlbs query 10.50.100.10 /passw WLBS Cluster Control Utility V2.3. (c) 1997-99 Microsoft Corporation Password: Accessing cluster ‘10.50.100.10’ (10.50.100.40): Host 7 (10.50.100.17) reported: converged Host 1 (10.50.100.11) reported: converged as DEFAULT Host […]

MRTG is a monitoring tool for traffic loads on network-links. It will create HTML pages with visual representation of both the current and historical load on the device. The server we will use for this article is the Gentoo box we built in this article. With Gentoo, we simply run emerge and a bunch of […]

In this article, we set up MRTG to monitor an old Cisco 1720 router. Now, it is nice to have *two* interfaces on a lab router so that you can route between two physical interfaces. We tried adding a second FastEthernet module instead of the T1 module we have, but the firmware was too old. […]

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 […]

There are some nasty, nasty SNMP vulnerabilities that have recently been revealed. Many different products are affected. See the CERT Advisory Here. This inspired us to upgrade our Cisco. To upgrade the IOS on your Cisco router, you have a couple of options. You can either upgrade via TFTP, or you can use the console. […]

We picked up a Watchguard Firebox FB-10R from RE-PC (Tukwila) for 15 bucks. There is almost always some kind of auction on Ebay selling a Firebox FB-10. The motherboard on ours, it turns out, was damaged. Now the Firebox FB-10R is just a regular PC clone. It has three 3COM 3C509 NICs in it. We […]