SeventhBit

BGP Border Gateway Protocol or BGP is an exterior gateway routing protocol or EGP. Exterior Gateway Routing Protocols are routing protocols used to route between autonomous systems. An autonomous system is just a way of saying a set of routers under a single administration. So, BGP is used to route between different autonomous systems, like between service providers as an example. BGP also can be used within an AS, which is referred to as iBGP and has different behavior than eBGP, which is used to route between different AS's. The image below, from vmware docs, shows what we are talking about with eBGP. The clouds represent a single autonomous system and the links between clouds are eBGP links allowing the exchange of routing information between AS's. Autonomous system numbers are how we represent each administrative domain. These numbers were 16-bit decimal numbers ranging from 0 - 65535 until RFC 4893, BGP Support for Four-Octet AS Number Space came out extending it

            DNS or the Domain Name System is a service that is provided to map layer 3 IP Addresses to names that we can remember. Since computers don't speak in terms of 'names' you need to have some sort of mapping service to tell the computer, what IP a certain name is referring to. This is a lot like a phone book(if your old) or a contact list on your phone. We, as humans, are not very good at remembering numbers so we create contacts in our phones that 'maps' a persons name to their phone number. This makes it easier for us to be able to communicate with a lot more people. This DNS service is usually ran on a server and there are DNS servers on your LAN as well as ones that service the Internet. These DNS servers handle the DNS queries that machines send when they need to figure out what a particular name maps to.       There are multiple types of queries - recursive, iterative, and non-recursive . Before we talk about the queries we must talk about the DNS re