Internal Gateway Protocol and external Gateway Protocol

Gateway-Gateway Protocol (GGP)

To Route packets correctly and efficiently, the core gateway needs to know the situation of other parts of the Internet, including routing information and subnet characteristics. This type of information is usually used when a gateway processes heavy loads and is the only way to access the subnet, other gateways in the network can cut traffic to reduce the load on the gateway.

GGP is mainly used to exchange routing information. Do not confuse routing information (including address, topology, and route delay details) with the routing algorithm. The routing algorithm is always fixed in the gateway and is not changed by GGP. The core gateways send GGP information and wait for a response to communicate with each other. Then, if a response containing specific information is received, the route table is updated.

Note that the latest GGP improvement SPREAD has been used in the Internet, but it is not as popular as GGP. GGP is called Vector-distance protocol. To work effectively, the gateway must contain complete information about all the gateways on the interconnected network. Otherwise, it is impossible to calculate a valid route to a destination. For this reason, all core gateways maintain a list of all core gateways on the Internet. This is a rather small table that the gateway can easily process.

External Gateway Protocol (EGP)

The external gateway protocol is used to transmit information between non-core neighboring gateways. Non-core gateways include the routing information of all directly adjacent gateways on the interconnected network and their connected machines, but they do not contain information of other gateways on the Internet. For the vast majority of EGP, only the LAN or WAN Information of their services is restricted. This prevents excessive route information from being transmitted between the LAN or WAN. EGP forces route information to be exchanged between non-core gateways.

Because the core gateway uses GGP and the non-core gateway uses EGP, both of which are applied on the Internet, there must be some ways for the two to communicate with each other. The Internet enables any autonomous (non-core) gateway to send "reachable" information to other systems. This information must be sent to at least one core gateway. If there is a larger autonomous network, it is often considered that there is a gateway to process the reachable information.

Like GGP, EGP uses a query process to let the gateway know its neighboring gateways and constantly exchange routing and status information with its peers. EGP is a State-driven protocol that relies on a state table that reflects the gateway situation and a group of operations that must be performed when the state table items change.

Internal Gateway Protocol (IGP)

There are several internal gateway protocols available. The most popular ones are RIP and HELLO. Another protocol is known as Open Shortest Path Priority Protocol (OSPF). None of these protocols are dominant, however, RIP may be the most common IGP protocol. Select a specific IGP based on the network architecture.

The RIP and HELLO protocols both calculate the distance to the destination. Their messages include the distance between the machine ID and the machine. Generally, because their route tables contain many items, messages are relatively long. RIP and HELLO maintain the 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 route table to Other gateways at regular 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 the time used by HELLO is not the distance used as the routing factor. This requires the gateway to have reasonable and accurate time information for each route. For this reason, the HELLO protocol depends on clock synchronization messages.

The Open Shortest Path priority protocol is developed by the Internet Engineering Task Group and is expected to become the dominant IGP. The routing process using the "Shortest Path" is inaccurate. The better name is "Optimal Path", which requires many factors to determine the optimal route to the destination.