What Is an Interior Gateway Protocol?

IGP (Interior Gateway Protocol) is a protocol that exchanges routing information between gateways (hosts and routers) within an autonomous network. Routing information can be used in Internet Protocol (IP) or other network protocols to explain how routing is carried out. IGP protocols include RIP, OSPF, IS-IS, IGRP, and EIGRP.

IGP (Interior Gateway Protocol) is a protocol that exchanges routing information between gateways (hosts and routers) within an autonomous network. Routing information can be used in Internet Protocol (IP) or other network protocols to explain how routing is carried out. IGP protocols include RIP, OSPF, IS-IS, IGRP, and EIGRP.

Chinese name

Interior gateway protocol

Foreign name

IGP

Including

RIP, OSPF, IS-IS, IGRP, EIGRP

Classification

Distance vector routing protocol

Internal and external protocol differences

The Internet is divided into multiple domains or multiple autonomous systems. A domain is a group of hosts and a collection of routers using the same routing protocol and is managed by a single organization. In other words, a domain may be the Internet managed by a university or other institution. The Interior Gateway Protocol (IGP) selects routes in a domain. The External Gateway Protocol (EGP) provides a method for exchanging messages and information between two adjacent routers located on the boundaries of their respective domains.

Classification of internal gateway protocols

Internal gateway protocols can be divided into two categories: distance vector routing protocols and link state routing protocols.

^[1] Distance vector routing protocol: Distance vector refers to a vector composed of distance and direction to advertise routing information. The distance is defined by metrics such as the number of hops, and the direction is the router or the outgoing interface of the next hop. Distance vector protocols often use the Bellman-Ford algorithm to determine the best path. Although the Bellman-Ford algorithm can eventually accumulate enough information to maintain a database of reachable networks, routers cannot understand the exact topology of the Internet through this algorithm. The router only knows the routing information received from neighboring routers.

The distance vector protocol is suitable for the following situations:

~ The network structure is simple and flat, and no special layered design is required.

~ The administrator does not have enough knowledge to configure and troubleshoot link state protocols.

~ Specific types of network topologies, such as Hub-and-Spoke networks.

~ No need to pay attention to the worst-case convergence time of the network.

^[2] Link-state routing protocol: A router configured with a link-state routing protocol can obtain information about all other routers to create a "complete view" (ie, topology) of the network. And choose the best path to reach all the destination networks in the topology (link state routing protocol is triggered to update, that is to say when there is a change).

The link state protocol is suitable for the following situations:

The network has been designed hierarchically, which is usually the case for large networks.

~ Administrators are familiar with the link-state routing protocols used in their networks.

~ The network requires extremely high convergence speed.

OSPF Interior Gateway Protocol OSPF

OSPF Open Shortest Path First is an Interior Gateway Protocol (IGP) for routing decisions within a single autonomous system (AS). In contrast to RIP, OSPF is a link state routing protocol, and RIP is a distance vector routing protocol. Link is another term for router interface, so OSPF is also called interface state routing protocol. OSPF establishes a link state database by advertising the status of network interfaces between routers, and generates a shortest path tree. Each OSPF router uses these shortest paths to construct routes. The main feature is the use of a distributed link state protocol instead of a distance vector protocol like RIP. Three main points: (1) Send information to all routers in the autonomous system. (2) The information sent is the link status of all routers adjacent to the router, but this is only part of the information known to the router. (3) Only when the link state changes, the router sends this information to all routers by flooding.

RIP Interior Gateway Protocol RIP

RIP (Routing Information Protocol), a routing information protocol, is the most widely used protocol in the interior gateway protocol. It is a distributed, distance vector-based routing protocol, which is characterized by a simple protocol. Suitable for relatively small autonomous systems, their diameter "hops" are generally less than 15. The characteristics of the RIP protocol are: (1) only exchange information with neighboring routes; (2) the information exchanged by the router is all the information known by the current router, that is, its own routing table. In other words, the information exchanged is: "My (shortest) distance to all networks in this autonomous system, and the next hop router to which that network should pass." (3) Exchange routing information at regular intervals, for example Every 30 seconds. The router then updates the routing table based on the received routing information.