Subnet Toolsand other network tips

The best ‘bug’ I have ever seen…


Way back in October 2013 Cisco slipped out this little field notice to customers and engineers across the globe. The position and function of the mode¬†switch is such that it can be pressed by the protective boot on certain types of cables and cause a reset to factory settings. Problem Description Certain types of snagless […]

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MAC Address Lookup Tool

This tool uses a copy of the Wireshark manufacturer database which is compiled from a variety of sources and is the most complete reference for MAC addresses that I have been able to find. This database includes the 24 bit vendor organisationally unique identifiers (OUI) as well as specifically reserved or commonly used MAC addresses […]

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Updated bulk MAC address lookup

In an earlier post I wrote a small powershell script to do lookups of vendor OUI. I have since updated this to use my own API which uses an up to date copy of the OUI database and now takes input of the filename of the list. MAC addresses still need to be in a […]

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Router migration using dual-as


I am working on a project that involves moving a router from one BGP ASN to another. The topology above shows the current situation and we want to move R2 to ASN20 and have it hooked up to R4 instead of R3. Normally this would be pretty trivial however the owner of R1 in ASN […]

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VRF Lite with redistribution between BGP and EIGRP


Some of my posts are just things that I was pretty sure worked but wasn’t 100% on how it worked and what the exact config looked like. In these situations if I can’t find something in a blog or on the Cisco site I post something to make it easier for the next guy trying […]

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Route summarisation

I found a very clever site that does route summarisation from a list. This is ideal if you dump out a copy of your routing table and want to see where the routes can be summarised. It’s also useful if you have subnets for a firewall rule that you want to consolidate.

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Getting your underpants inside out over NAT


A colleague asked me to write a post on NAT and so this one is for him. I’m going to use a very basic three router lab to go through the common types of NAT and where they are used. First off there is the convention of inside and outside interfaces.¬†The golden rule here is […]

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Logical look at masks


Having done an introduction to wildcard masks and the cool things you can do with them I thought it might be worth writing about the logic behind both subnet masks and wildcard masks. Masks use two of the most basic logical functions that computers can perform, a logical AND and a logical OR. Logical AND […]

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Getting Wild[card masks]


If you ask most people what a wildcard mask is they’ll probably say it’s an inverse subnet mask. That is a massive under-representation of the power of a wildcard mask and does not do fair justice to the range of useful tricks you can do with a wildcard mask. We’ll start with why people think […]

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Stats on concurrent SSL VPN sessions.


In the past I always used ‘sh cry is sa’ to give me a view of the number of concurrent VPN sessions on an ASA. I am involved in an Anyconnect SSL VPN roll out and today I was asked to pull off stats on how many users are connected to each solution. The following […]

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