Clavister Firewalls: Top 5 useful console commands

This document provides a short description of the most widely used Clavister (click here for more information) console commands from experience. Note: for more information about any of the commands listed below, please type in help [command]. The below commands apply to Clavister CorePlus v8.9.x pcapdump This command starts up the packet capture mechanism on … Continue reading Clavister Firewalls: Top 5 useful console commands

Bringing IPv6 to the home : Part 2

The article is a more in-depth look at residential IPv6, the final installment of the 2 part series. If you've missed it, the 1st article can be found here. After having established a successful connection to an IPv6 broker server, I fired up wireshark to see what is going on over the wire. We immediately … Continue reading Bringing IPv6 to the home : Part 2

Bringing IPv6 to the home : Part 1

World IPv6 day came and went, but for most of us nothing much changed. In Malta especially, there currently seems no interest for ISPs to start using IPV6, very probably due to the challenges it poses. So I went on a mission to bring IPv6 connectivity to my home network (FYI, there are already some … Continue reading Bringing IPv6 to the home : Part 1

Using OpenNetAdmin for network documentation

It’s probably a familiar situation for every sysadmin… at some stage, your network grows to be too large for your trusty spreadsheet to keep track of. In enterprise networks this is especially true, where the number of servers can easily be in the hundreds. While looking for a good, open source solution to this problem, … Continue reading Using OpenNetAdmin for network documentation

Cisco network traffic monitoring with NfSen/NfDump and NetFlow

A while ago I wrote a quick article on using NTOP to monitor network utilization by using cisco’s NetFlow functionality. This is an excellent tool, and it’s high level reporting is definitely a strength. However, I was after a more detailed report about what happened when. In a network, it is often necessary to keep … Continue reading Cisco network traffic monitoring with NfSen/NfDump and NetFlow

Using cisco’s embedded event manager to aid in troubleshooting

In my previous post I explained a setup in which multiple cisco nodes send syslog messages to a centralised syslog server which network admins would check during troubleshooting. As an extension to that, we had another requirement proposed. To facilitate troubleshooting, we wanted to display the interface description when an error occurred on an interface. … Continue reading Using cisco’s embedded event manager to aid in troubleshooting

TCP zero windows

Yet another reason downloads can fail… Issue : Large file is being downloaded (eg an ISO running above 500MBs). The file starts off downloading fine, but eventually stops downloading, leaving the file incomplete. Cause (in this case) : TCP zero windows caused the server to reset the connection Troubleshooting : In wireshark, run the following … Continue reading TCP zero windows