Original computing articles by a systems administrator

Category Archives: Networking

Creating a Histogram of TCP Window Sizes from a Packet Capture using Python

Although wireshark is a very useful tool there are some limitations that bother me: Wireshark Out of Memory errors can be frustrating Although advanced IO graphing provides a lot power it is still limited I have found that scapy and pylab can fill some of the gaps. Here is an example using the python interactiveContinue Reading

Cisco Lab: Router Redundancy with BGP and HSRP

Introduction: From what I have learned there are at least two typical scenarios for WAN level redundancy with BGP that you would use in a co-location environment. The first is when you get an AS from ARIN, and advertise your IP block to two different providers so you become an edge (aka border) router onContinue Reading

Quick Tip: Trick Not to Lock Yourself Out when Remotely Administering Cisco Routers

I remotely administer Cisco routers, which can be a bit stressful since I need make sure not lock my self out by do something like removing a NAT command, editing ACL, or screwing up a VPN tunnel. A Cisco support person pointed out to me that I can use the reload command to schedule reboots,Continue Reading

Moving a Front-End Exchange 2003 Server into your DMZ

Introduction: A common practice in networks is to have at least two Exchange servers, a front-end server in the demilitarized zone (DMZ, perimeter network in Microsoft terminology) and a back-end server in the company’s main network.  The front-end server hosts the public SMTP server and web mail.  The back-end server hosts the actual mail (informationContinue Reading

How-to: Setup up an Emulated Cisco Lab Using GNS3 in Ubuntu, Part1

Introduction: GNS3 is a graphical network simulator that is integrated with the Cisco router emulator Dynamips.  In this tutorial I will explain how to connect your Linux host to an emulated 7200 series router, then that router to another 7200 router, and finally that second router will be connected to a Linux VM running inContinue Reading