Month: April 2014

BGP communities

O men, when you start to write about BGP it is probably the time then you seriously start questioning yourself where did I go with myself. That is probably the moment in which you realize that there is a network geek sitting somewhere inside you. At least that is what happened to me when I finished to write this huge post. Don’t be scared, it’s fun to know about this thing below.

Simple start

Every local network is managed by his own network administrator. If the network become big enough and there are more than few sub-segments inside that network there will probably be some kind of routing protocol running inside. That routing protocol will be IGP or interior gateway protocol more probably OSPF as it’s vendor independent.

When we want to connect our network to other networks across the world, we are trying to connect it to the internet. The Internet is the network connecting most of the networks today and in that way it became the biggest inter-networking system in the world. To be able to get that huge network to function and get our LANs to act jointly there must be a routing protocol that enables it.

BGP – Border Gateway Protocol is that one.

Every individual network has his own policies that are enabling that network to behave as the administrator want. When connection networks to the internet network all those policies need to be tied together with BGP protocol in order to influence outside communication entering the local network and communications initiated from the local network going outside somewhere on the internet. This is done using more that few different BGP attributes. Those attributes are forwarded across specific prefixes. Sometimes those attributes are not only forwarded but also modified on the way, one of which is the community attribute.

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VXLAN – Virtual Extensible LAN

As the time goes by and the network with more and more virtualised servers and other devices are making that network more complicated, overlay technologies are rising to save the day for network administrators.

Virtual Extensible LAN – VXLAN is a new encapsulation technology used to run an overlay network on current Layer 3 communication network. An overlay network is considered as a practical network that is set up on the top of current layer 2 network. It also considers additional layer 3 technologies to aid flexible computer architectures. VXLAN will make sure it is very easy for network engineers to level out the right cloud computing setting while reasonably separating cloud applications and tenants. A cloud computing environment is defined as a multitenant, every tenant needs its separately configured logical network, which in return needs it’s very own network ID or identification.

What the hell that means?

What it this VXLAN doing actually. To put it simple, VXLAN can create logical network to connect your virtual machines across different networks. It is enabling us to make a layer 2 network for our VMs on top of our layer 3 network. That’s why VXLAN is a overlay technology. In “normal” network if you are connecting virtual machine to get the connection to some other virtual machine on different subnet, you need to use a layer 3 router to make a connection between networks. With VXLAN we can utilize VXLAN gateway of some sort to connect them without even exiting into physical network.

VXLAN frame

Image: VXLAN frame – taken from blog.cisco.com website

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