Category: Network Fundamentals

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GRE Tunnels and VRFs

GRE Tunnelling. It’s a tool that should be in every network engineer’s toolbox, but not one we like to use very often. But sometimes, it’s needed. Sometimes you need to just make something work, across somebody else’s network. This week’s task is to do just that, in support of an office migration for a client.

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Design Consideration – The effects of VLAN ID’s on Spanning-Tree convergence

When designing a network, consideration should be given to separating traffic into VLANs. This is done for logical separation, security and performance reasons. This affects the convergence of a Layer 2 Network. Most Cisco switches running STP (Spanning-Tree Protocol) will be running an instance per VLAN. This is called PVST (Per VLAN Spanning-Tree), or RPVST

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What is ARP?

A number of times in the last few weeks I have been asked by a number of people: What is ARP? There is the simple answer – which is simply a definition: Address Resolution Protocol (ARP) is a mechanism to resolve IP addresses into MAC addresses. However…that doesn’t really explain a lot. It probably doesn’t

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Why am I seeing packets on my server that aren’t for this server?

While troubleshooting a totally unrelated issue, one of my colleagues noticed that they were seeing packets in a tcpdump that were neither destined for nor sourced from the server. This is odd, when plugged into a switch, so we started digging. Server 1, was sending a stream of packets to Server 2 – in a