What Is a Routing Protocol?

Routing protocol (English: Routing protocol) is an online protocol that specifies how data packets are forwarded. The main node device of the Internet network is a router, and the router forwards the received data through a routing table. Forwarding policies can be manually specified (through static routing, policy routing, etc.). In networks with smaller scales, there is no problem in manually specifying the forwarding strategy. However, in a large-scale network (such as a multinational enterprise network or an ISP network), if you manually specify a forwarding policy, it will bring a huge workload to the network administrator, and it will also become difficult to manage and maintain routing tables Very difficult. To solve this problem, a dynamic routing protocol came into being. Dynamic routing protocols allow routers to automatically learn the networks of other routers, and automatically update the routing table when the network topology changes. The network administrator only needs to configure a dynamic routing protocol, and the workload is greatly reduced compared to manually specifying a forwarding policy.

The routing protocol passes in

The routing protocol mainly runs on

Common routing protocols include RIP, IGRP (Cisco Proprietary Protocol), EIGRP (Cisco Proprietary Protocol), OSPF, IS-IS, BGP, and so on.

RIP, IGRP, EIGRP, OSPF, and IS-IS are Interior Gateway Protocols (IGPs). They are applicable to the operation of a unified routing protocol for a single ISP. Generally, a network operated by an ISP is located in an AS (autonomous system), and there is a unified AS. number (autonomous system number). BGP is a routing protocol between autonomous systems and an external gateway protocol. It is mostly used to exchange routing information between different ISPs, as well as large-scale private networks such as large enterprises and governments.

RIP Routing Protocol RIP

Main article: Routing Information Protocol

RIP has long been used on the Internet and is the simplest routing protocol. It is an abbreviation of "Route Information Protocol", which mainly transmits routing information, maintains the relationship between adjacent routers by broadcasting the routing table every 30 seconds, and calculates its own route based on the received routing table information. Table information. RIP is a distance vector routing protocol with a maximum hop count of 15 hops. A network exceeding 15 hops considers the destination network unreachable. This protocol is usually used in small network environments where the network architecture is relatively simple. Now divided into two versions of RIPv1 and RIPv2, the latter supports VLSM technology and a series of technical improvements. RIP has a slower convergence rate.

OSPF Routing Protocol OSPF

Main article: Open shortest path first

The OSPF protocol is an abbreviation of "Open Shortest Path First" and belongs to a link-state routing protocol. OSPF introduced the concept of "area". All routers in each area maintain the same Link State Database (LSDB). Areas are divided into backbone areas (the backbone area must be numbered 0) and non-backbone areas (non-zero numbered areas). If a single area exists on a network running OSPF, the area can be a backbone area or a non-backbone area. If there are multiple areas in the network, there must be a backbone area, and all non-backbone areas must be directly connected to the backbone area. OSPF uses the maintained link state database to calculate the routing table through the shortest path first algorithm (SPF algorithm). OSPF converges faster. Due to its unique openness and good scalability, the OSPF protocol is currently widely deployed in various networks.

IS-IS Routing protocol IS-IS

Main article: Intermediate system to intermediate system

The IS-IS protocol is an abbreviation of Intermediate system to intermediate system. It belongs to the link-state routing protocol. The standard IS-IS protocol is defined by ISO / IEC 10589: 2002 formulated by the International Organization for Standardization. The standard IS-IS is not suitable for IP networks. Therefore, the IETF has developed an integrated IS-IS protocol (Integrated) for IP networks. IS-IS). Like OSPF, IS-IS also uses the concept of "area". It also maintains a link state database and calculates the best path through the shortest spanning tree algorithm (SPF). IS-IS has a faster convergence speed. The integrated IS-IS protocol is the most commonly used IGP protocol on the ISP backbone network.

IGRP Routing protocol IGRP

Main article: Interior gateway routing protocol

The IGRP protocol is an abbreviation of "Interior Gateway Routing Protocol". It was independently developed by Cisco in the 1980s and belongs to the Cisco proprietary protocol. IGRP, like RIP, is a distance vector routing protocol, so it has similarities in many aspects. For example, IGRP is also a periodic broadcast routing table with a maximum number of hops. Up). The biggest feature of IGRP is the use of mixed metric values, while considering the link bandwidth, delay, load, MTU, and reliability to calculate routing metric values, unlike other IGP protocols that simply consider one aspect. Calculate the metric. At present, IGRP has been replaced by the EIGRP protocol independently developed by Cisco. The Cisco IOS (Internetwork Operating System) version 12.3 and above does not support this protocol anymore, and there are few networks running the IGRP protocol.

EIGRP Routing protocol EIGRP

Main article: Enhanced internal gateway routing protocol

Due to various defects and shortcomings of the IGRP protocol, Cisco developed the EIGRP protocol (Enhanced Interior Gateway Routing Protocol) to replace the IGRP protocol. EIGRP is an advanced distance vector routing protocol (also known as a hybrid routing protocol). It inherits IGRP's hybrid metric. The biggest feature is that it introduces non-equal cost load balancing technology and has extremely fast convergence speed. The EIGRP protocol is widely deployed in Cisco equipment network environments.

BGP Routing Protocol BGP

Main article: Border Gateway Protocol

In order to maintain the independent interests of each ISP, the standardization organization has formulated the routing protocol BGP between ISPs. BGP is an abbreviation of "Border Gateway Protocol", which handles routing transmission between ISPs. However, BGP runs at a relatively core position and requires users to have a good understanding of the structure of the network, otherwise it may cause greater losses. ^[1]