A Brief Introduction to the working mechanism of BGP protocol

In network protocols, the use of BGP is complex to many extent. This is caused by different IP addresses of different hosts, different network connections, different terminals and hardware interfaces. Therefore, there are many types of routing protocols in our network protocols. BGP is an external gateway protocol designed for TCP/IP Internet and used between multiple autonomous domains. It is neither based on pure link state algorithms, it is not based on pure distance vector algorithms. Its main function is to exchange network accessibility information with BGP in other autonomous domains. Each autonomous domain can run different internal gateway protocols. BGP updates include the paired information of the network number/autonomous domain path. The autonomous domain path includes the autonomous domain string to be passed to a specific network, these updates are transmitted over TCP to ensure transmission reliability ｡

1. BGP protocol Introduction

BGP (Border Gateway Protocol) is a dynamic routing discovery Protocol between autonomous systems. Three earlier versions of BGP were released as BGP-1 (see RFC1105), BGP-2 (see RFC1163) and BGP-3 (see RFC1267), the current version is BGP-4 (see RFC1771). BGP-4 applies to distributed structures, CIDR (Classless Inter-Domain Routing) supports Classless Inter-Domain Routing. BGP can also be used to implement user-configured policies ｡

BGP-4 is rapidly becoming the de facto Internet external routing protocol standard, and BGP is often used between ISPs ｡

2. BGP Working Mechanism

The BGP system runs on a specific router as a high-level protocol. When the system starts, the BGP router exchanges route information by sending the entire BGP Route table and peer, and then only exchanges update messages) the system checks whether the connection is normal by receiving and sending the keep-alive message ｡

The router that sends a BGP message is called the BGP speaker. It continuously receives or generates new route information and advertises it (advertise) to other BGP spokespersons. When a BGP spokesman receives a new route advertisement from other autonomous systems, if the route is better than the current known route, or the current route is not yet available, it advertises this route to all other BGP spokespersons in the autonomous system. a bgp spokesman also calls the other BGP spokespersons that exchange messages with it peer ), A number of related peers can form a peer group )｡

The BGP protocol runs in the following two modes on the vro:

IBGP (Internal BGP)

EBGP (External BGP)

When BGP runs inside the same Autonomous System (AS), it is called IBGP. When BGP runs between different autonomous systems, it is called EBGP ｡

The BGP protocol machine runs through message-driven messages. There are four types of messages: open messageupdate, notification message, messagekeep-alive, and message.

An open message is the first message sent after a connection is established. It is used to establish a connection relationship between BGP protocol peers ｡

Notification message is an error notification message ｡

Keep-alive message is a message used to check the connection validity ｡

Update message is the most important information in the BGP system. It is used to exchange route information between peers. It consists of up to three parts, namely unreachable and path attributes) and network accessibility information NLRI (network layer reach/reachable information )｡