Common classification of routing protocols

Gateway-Gateway Protocol (GGP)

The core gateways need to know what is happening in other parts of the Internet, including routing information and subnet features, in order to route messages correctly and efficiently.

This type of information is typically used when a gateway handles heavy load and makes the speed especially slow, and the gateway is the only way to access the subnet, and other gateways in the network can tailor traffic to reduce the load on the gateway.

GGP is primarily used for exchanging routing information, not confusing routing information (including address, topology, and routing delay details) and algorithms that make routing decisions. Routing algorithms are usually fixed within a gateway and are not GGP changed. The core gateways communicate with each other by sending GGP information and waiting for an answer, and then updating the routing table if they receive a response that contains specific information.

Note that GGP's latest improvements spread already used on the Internet, but it's not as popular as GGP. GGP is called the vector-distance protocol. To work effectively, gateways must contain complete information about all gateways on the Internet. Otherwise, it would be impossible to compute a valid route to a destination. For this reason, all the core gateways maintain a list of all the core gateways on the Internet. This is a fairly small table that the gateway can easily handle.

External Gateway Protocol (EGP)

The external gateway protocol is used to transmit information between non-core neighboring gateways. Non-core gateways contain the routing information and the machine information of all the gateways directly adjacent to the Internet, but they do not contain information about other gateways on the Internet. For most EGP, only the LAN or WAN information that maintains its services is restricted. This prevents excessive routing information from being transmitted between a local area network or a wide area network. EGP enforces the exchange of routing information between Non-core gateways.

Because core gateways use GGP, and Non-core gateways use EGP, both of which are applied to the Internet, there must be some way to communicate between the two. The internet enables any autonomous (Non-core) gateway to send "accessible" information to other systems, at least to a core gateway. If there is a larger autonomous network, it is often assumed that there is a gateway to handle these accessible information.

Like GGP, EGP uses a query process to let the gateway know its neighboring gateways and continuously exchange Routing and state information with its neighbors. EGP is a state-driven protocol that means it relies on a state table that reflects the gateway situation and a set of actions that must be performed when the state table entry changes.

Internal Gateway Protocol (IGP)

There are several internal gateway protocols available, the most popular are rip and Hello, and the other is called Open Shortest Path Priority Protocol (OSPF), none of which is dominant, but rip may be the most common IGP protocol. Select specific IGP to be based on the network architecture.

Both the RIP and Hello protocols compute the distance to the destination, and their messages include the machine identification and the distance to the machine. Generally speaking, because their routing table contains many items, the message is relatively long. RIP and Hello always maintain connectivity between neighboring gateways to ensure that the machine is active.

The Routing Information Protocol uses broadcast technology. It means that the gateway broadcasts the routing table to other gateways at certain intervals. This is also a problem with RIP because it increases network traffic and reduces network performance.

The difference between the Hello protocol and RIP is that Hello uses time rather than distance as a routing factor. This requires that the gateway have reasonable accurate time information for each route. For this reason, the Hello protocol relies on clock synchronization messages.

The Open Shortest Path priority protocol is a protocol developed by the Internet Engineering Task Force, and it is hoped that it will become the dominant IGP. The routing process describing the protocol with "shortest path" is inaccurate. A better name is the "best path", which takes many factors into account to determine the best route to the destination.