BGP Basic Nomenclature BGP speaker – A router that implements BGP BGP identifier – Unique identifier of BGP speaker (IP address) Autonomous System (AS) -The classic definition of an Autonomous System is a set of routers under a single technical administration, using an interior gateway protocol (IGP) and common metrics to determine how to route  Full Article…

BGP Autonomous Systems An AS is a collection of networks under a single technical administration IGP operates within an AS BGP is used between ASs Exchange of loop-free routing info is guaranteed BGP features Open standard Exterior – designed for Inter-AS Domain Routing Designed to scale huge inter-network like Internet classless (supports VLSM, CIDR, auto  Full Article…

Single homed site a site with a single connetion to ISP is called single homed either use static routes, or advertise the site routes to the ISP and receive default route from ISP when customer is connected to SP via static routes, traffic from that customer on Internet is indistinguishable from traffic from the ISP –  Full Article…

BGP neighbors are routers forming TCP connection for exchanging BGP updates. They are also called BGP Peers or BGP Speakers. There are two types of BGP relationship: IBGP (Internal BGP) EBGP (External BGP) BGP Databases Neighbor table a list of all configured BGP neighbors neighbor has to be manually configured using neighbor command we have  Full Article…

Configuring BGP routing protocol #router bgp {AS no.}  #network {network ID} mask [subnet mask] – When you dont put mask the router will assume default classfull mask  #neighbor {IP address} remote-as {AS No.} BEWARE!! In BGP there is rule that states: router looks exactly what you type in network command with the mask also! If  Full Article…

In BGP there are two loop prevention mechanism: for EBGP there is AS-Path attribute which states that router will drop BGP advertisement when it sees it own AS number in AS path attribute for IBGP there is split horizon rule which states that update sent by one IBGP neighbor should be not send to another  Full Article…

Active neighbor It may happen that your neighborship is in state Active or Idle. It means that router has sent an open packet and is waiting for response. There could be several reasons for that: neighbor is peering with a wrong IP address neighbor doesnt have neighbor statement for this router AS number is missconfigured Interface  Full Article…

BGP supports authentication mechanism using MD5 mechanism. When authentication is enabled every TCP segment belonging to BGP session is verified and accepted only if the authentication match. If authentication fails, the BGP relationship is not established. You may configure BGP authentication with the command #neighbor {IP address | peer group name} password {XXX}

Peer groups simplifies the configuration by allowing to apply same policy rules to more neighbors. Updates are generated once per peer group. You configure new peer group by following commands: #neighbor {name of peer group} peer-group – you create peer group with its name #neighbor {name of peer group} remote-as {number} – you set the  Full Article…