Border Gateway Protocol

Kashif Latif

What is BGP…?Border Gateway Protocol (BGP) is the protocol which is backing the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reach-ability among autonomous systems (AS).

It is described as a path vector protocol (which maintains the path information that gets updated dynamically).

Count… BGP is one of the most important protocols of

the Internet. BGP was created to replace the Exterior

Gateway Protocol (EGP) to allow fully decentralized routing.

BGP is used internally between the gateways to determine which gateway offers the best route to a given destination network.

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.

Types of BGP SessionsWhile the stated purpose of BGP is to allow for the conveyance of routing information between autonomous systems. Clearly, BGP routers must communicate differently when they share a common AS (as opposed to being in different ASs). In fact, this is the distinction between 1. Internal BGP (IBGP)2. External BGP (EBGP)

These two variations on the same protocol act virtually the same in most instances. The differences between them lie in three areas.3. Routing update processing4. Handling of route attributes5. Connectivity requirements

BGP Message TypesThere are four types of BGP messages, each with its own role in setting up, maintaining, or tearing down a BGP peering session.They are listed below:1. OPEN messages2. UPDATE messages3. KEEPALIVE messages4. NOTIFICATION messages

None of these messages may be exchanged until two BGP routers have first set up a TCP session between themselves on port 179. Errors on that TCP link will trigger BGP NOTIFICATION messages that will close the connection.

BGP Attribute Categories

Attributes are used in the routing decision process. They might also be used in the input and output policy definition process.The four categories of attributes are described below:

1. Well-known Mandatory2. Well-known Discretionary3. Optional Transitive4. Optional Nontransitive

BGP Routing ProcessMost 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 ProblemsWith 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 scalability2. Instability3. Routing table growth4. Load-balancing problem5. 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

Thank

You…!

Kashif Latif