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IP Routing Functions


There is no doubt that one of the most important functions of the Internet protocol (IP) is that of routing.   The datagrams that are routed by IP can be generated either on the local host or another remote device.  If they are generated from a remote host, then in order to process the datagram it…

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Introducing Snort – Open Source NIDS


Anyone who has studied or spent time working in network security will have heard of Snort.  It is an open source NIDS (Network Intrusion detection System) which has been installed on millions of systems across the world.  It was written initially as a packet sniffer by Marty Roesch but is now supported by many more…

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UDP – User Datagram Protocol


UDP is a relatively simple protocol compared with something like TCP for one simple reason – it has none of the fields that ensure reliable delivery of information.  With UDP there is no guarantee that data transmitted will be delivered, the idea is that applications and other transport mechanisms will handle this function. However there…

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DNS Caching for Proxies


Resolving names can often lead to performance issues on busy networks.  For instance in most large networks internet access is handled through central proxies, mainly for security reasons.  Organisations can control access to the internet if all traffic is funneled via a specific server, these can also be the only machines allowed through a firewall…

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Authentication Systems and Techniques


Authentication is one of the most important parts of any computer system, application or network.  Without an adequate authentication method a network operating system will quickly become overloaded and insecure.  In the early days of computers a simple username and password would be sufficient, and although this is still the case in many networks more…

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Capacity Planning for Proxy Servers


There is one factor which is crucial when we are considering capacity planning for a proxy server and that is the ‘peak load’.  This point will vary greatly between organisations or companies yet it is essential that it is first identified and measured correctly.  For some networks it might be first thing in the morning…

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Network Troubleshooting – TCP Flow Control


This is the 2nd article in our series on troubleshooting network performance problems, in it we are going to look at another area which will help this function. Retransmissions and duplicate ACKs are part of TCPs functionality which helps prevent packet loss.  If you have network or server performance problems then it’s likely you will…

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Troubleshooting a Slow Network – Introduction


Over the years I’ve worked in IT, this is probably the most common and frustrating issue I’ve seen in corporate networks. It’s often extremely hard to solve and often has a huge impact on all aspects of an organisation. When you sit and watch a domain logon take over twenty minutes regularly on a state…

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Address Resolution Protocol – ARP


On a network both physical and logical addresses play a role in communication.   The use of logical addresses allows for the communication between more than one single network and also access to devices that may not be directly connected to that network.  Whereas Physical addresses are primarily used to facilitate communication on the single…

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Learning to Dissect Packets


For many years if you wanted to analyse the data on your network you needed expensive tools and software.  However nowadays this isn’t the case, there are now a whole host of free tools which you can use in addition or even instead of the commercial options.  It might sounds a little unnecessary to actually…

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