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BGP (Border Gateway Routing Protocol)

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BGP (Border Gateway Routing Protocol) BGP (Border Gateway Routing Protocol) is a standardizedexterior gateway protocol designed to exchange routing and accessibility information between autonomous systems (AS) on the Internet. The Border Gateway Protocol makes routing decisions based on paths, network policies or rule-sets configured by a network administrator, and are involved in making core routing decisions. BGP is a very robust and scalable routing protocol, as evidenced by the fact that BGP is the routing protocol employed on the Internet. INTRODUCTION It is a routingprotocol. RIP and OSPF are interior for exchanging routing information between gateways (commonly routers) within an Autonomous System (for example, a system of corporate local area networks). so BGP is different from these protocols. it is ERP(exterior routing protocol) which is used to connect two or more autonomous systems. it connects two or more organization networks with each otherand may be used bya single big organization to connect theirsystems. It is used by ISP(internet service provider) like(BSNL,MTNL,DOLPHIN etc.)that's why it is also known as routing protocol of internet. Introduction(Conti…) If any big organization having two or more internet connections then in this situation they can also use this BGP protocol to connect with more than one ISPs to keep connection with all ISP’s internetconnection. This is known as multi homing. Multi homing refers to a computeror device connected to more than one computer network. It can be used, for example, to increase the reliabilityof an Internet Protocol network, such as a user served by more than one Internet service provider. History Before bgp there was an exteriorgateway protocol(egp). It got replaced by BGP and since 1994 we are using BGPv4. And it supports CIDR method means classless internetdomain routing with the help of this we can perform subnetting and supernetting. we can also keep our routing table small and effective. OSPF is link state protocol and RIP is a distance vectorprotocol. But BGP is neither link state ordistance vector.it is path vectorrouting protocol. routing decisions are made basedon: 1.path 2.network policies. 3.rules 4 Types of messages 1.Open: . In this firstly we create a connection with TCP. After this we can send an open message. Open message carries several parameters thorough which they check validity of each of them . These parameters decide thatwe should communicateor not . .That can be agreed by BGPneighbors(AS). 2.Update: . After getting open message we can send update message. It contains the actual rout updates. It composedof: o NLRI(network layer reachability). o AS-path. o AS-attribute. Types of messages 3.Keep alive: . Keep the session running when there are no updates. Let BGP speakers know that they are still there. If we don’t get any keepalive message then BGP will remove all the informations about that particular peer which was stored in the routing table. 4.Notification: . It is used to send the error message. It may be any kind of messagelike: o Update corrupt message. o If router needs to turn off a session unexpectedly. BGP states Idle:it starts TCP connwith BGP peers.it won’t acceptBGP connetion until Tcp conn isestablished. Connect:after tcp connect,.peersends open msg to peer. Active state:if tcp is unsuccessful then it stays in active state . Restart theprocess. Open sent :if connect state is sucessful.open msg arelistened and validity is of msg ischecked. If open sent is successful send keepalivemesssage Keepalive msg:maintains the sessions .contains timer. Open confirm:bgprouter recieves keepalive msg. If success the established state; Established:if successful ,Bgp protocol exchanges updated routing info. Among routers involved in thecommunication. Communication It uses TCP port no179. TCP used for reliability. Because it sendsacknowledgment. Slowest routing protocol. Actually it is designintentionally to be slow because by this it can take routing decision slowly because in internet ,links and networks goes up and down time by time if it will take fast decision then may be which link or network went down will go up after some time then it has to take routing decision again. So it will consume more energy to routeand we wouldn't be use other network resourcesproperly. BGP terminology BGP Peers and peering: *BGP neighbors are known as BGPpeers. *when BGP routers exchange routes with another BGP called peering. *in this we can establish peering by manual configuration. BGP Peering Peering is the term used to describe the transit arrangements between ISPs. There are really two levels of peering, either you are a peer or a client. Peer networks agree to carry traffic of a peer without charging for it. Connections between networks can be private point-to-point links or through an exchange. Many NSPs are tending to move to private connections due to the overload situation at many of the NAPs. BGP is the protocol used to exchange routing information between the various networks. BGP AS(Autonomous system) Autonomous systems are group of routers. They share similar routingpolicies. Operatewithin a single administrative domain. Typically belongs to oneorganization. AS numbers can be between 1 to65535. TYPES OF AS Types of AS system: 1.Stub AS: it has only connection to the anotherAS. The host in the AS can send data traffic to other AS similary it can receive data coming from other AS. However, the data can’t be pass through the stub AS because it acts as a sourceora sink. Ex: local ISP. 2. Multi homing:Multi homing refers to a computerordevice connected to more than one computer network. It can be used, for example, to increase the reliability of an Internet Protocol network, such as a user served by more than one Internetservice provider. 3. Transient: It is also a multihome ISP that supports transientdata. Ex:NSPs and ISPs. BGP NLRI The Network Layer Reachability Information (NLRI) is exchanged between BGP routers using UPDATE messages. An NLRI is composed of a LENGTH and aPREFIX. The length is a network mask in CIDR notation (eg. /25) specifying the number of network bits, and the prefix is the Network address for that subnet. The NLRI is unique to BGP version 4 and allows BGP to carry supernetting information, as well as performaggregation. The NLRI would look something like oneof these: /25, 204.149.16.128 /23, 206.134.32 /8, 10 Only one NLRI is included in an UPDATE Message, though there may be multiple AS-paths and AS-pathattributes. BGP Types 1.Internal BGP(I-BGP): Neighbors that belong to the same AS. These neighbors needn't to be directly connected. 2.External BGP(E-BGP): Neighbors that belong to the different AS. These neighbors need to be directlyconnected. BGP Attributes The matrix used by BGP are called path attributes. -as path. -next hop. -local preference , etc. BGP Routing Process Most routing protocols receive routing information, use it to build and maintain a routing table, and share that table (or a subset of the table) with other routers in the network. BGP Problems With a lots of benefits and importance of BGP in network, it also have some problem on it’s maintenance. The main problems are follow: 1. Internal BGP scalability 2. Instability 3. Routing table growth 4. Load-balancing problem 5. IP Hijacking Implementations Bird Internet routing daemon, a GPL routing package for Unix-like systems. GNU Zebra, a GPL routing suite supporting BGP4. OpenBGPD, a BSD licensed implementation by the OpenBSD team. Quagga, a fork of GNU Zebra for Unix-like systems. XORP, the extensible Open Router Platform, a BSD licensed suite of routing protocols. VNE, a C# software library implementing BGP .
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