What Is a Gateway Page?

Gateway (Gateway) is also called internet connector, protocol converter. The gateway realizes network interconnection above the network layer. It is a complex network interconnection device and is only used for network interconnection between two high-level protocols. The gateway can be used for both WAN interconnection and LAN interconnection. A gateway is a computer system or device that acts as a conversion task. Used between different communication protocols, data formats or languages, and even between two systems with completely different architectures, the gateway is a translator. Unlike a bridge that simply conveys information, the gateway repackages the received information to meet the needs of the destination system. In the same layer-the application layer.

Everyone knows that from one

Suppose your name is

The current IPV4 IP address is 32-bit, and is divided into three types of addresses: A, B, and C according to the first few digits. However, due to the rapid development of the Internet, IP resources are drying up, and fewer and fewer IP addresses are available for distribution. It is in serious conflict with the development of the Internet.

The full name of the RIP protocol is a routing information protocol, which is a

OSPF (OpenShortestPathFirst) is an Interior Gateway Protocol (InteriorGatewayProtocol, referred to as

If two routers that exchange routing information belong to two autonomous systems, they are called exterior neighbors, but if they belong to the same autonomous system, they are called interior neighbors. The protocol used by external neighbors to advertise reachability information to other autonomous systems is called the Exterior Gateway Protocol EGP (ExteriorGatewayProtocol), and the routers that use this protocol are called exterior routers. In the Internet, EGP is particularly important because the autonomous system connected to it uses it to advertise reachability information to the core system.

Gateway Three Functions

The first is that it supports the neighboracquisition mechanism, which allows one router to request another router to agree to exchange reachable information. We can say that a router acquires an EGP peer router (EGPpeer) or an EGP neighbor (EGPneighbor). EGP peer routers are neighbors only in the sense of exchanging routing information, regardless of their geographical proximity.

Second, the router continuously tests whether its EGP neighbors can respond.

Third, EGP neighbors periodically send routing update messages to exchange network reachability information.

Like GGP, EGP uses a query process to make the gateway aware of its neighboring gateways and continuously exchange routing and status information with its neighbors. EGP is a state-driven protocol, which means that it relies on a state table that reflects the condition of the gateway and a set of operations that must be performed when the state table entry changes.

Gateway nine message types

EGP message header: In order to achieve the above three basic functions, EGP defines the nine message types listed in the table below:

AcquisitionRequest requests the router to become a neighbor (peer router)

AcquisitionConfirm A positive response to an acquisition request

AcquisitionRefuse A negative response to an acquisition request

CeaseRequest (cancel request) request to terminate the neighbor relationship

CeaseConfirm Acknowledgement response to a request to abort

Hello (Hello) ask the neighbor to answer whether it is active

IHeardYou's answer to the Hello message

PollRequest (poll request) request to update the routing of the network

RoutingUpdate network reachability information

Error response to incorrect message

All EGP messages have a fixed header to describe the message type. The version field in the header takes an integer value and indicates the version number of the EGP used in the message. The receiver checks the version number to confirm that both parties use the same version of the protocol. The TYPE field indicates the type of the message, and the CODE field gives the subtype. The STATUS field contains status information related to this message. EGP uses the checksum field to confirm the correct arrival of the message. Its algorithm is the same as the checksum algorithm of IP. It treats the entire EGP message as a sequence of 16-bit integers, and uses the binary inverse of each integer as the checksum. Before calculating the checksum, initialize the CHECKSUM field to zero, and fill the zero to change the message length to an integer multiple of 16 bits. The Autonomous System Number (AUTONOMOUSSYSTEMNUM) field gives the number of the autonomous system in which the router sending the message is located, and the sequence number (SEQUENCENUMBER) is used for sending and receiving parties to communicate. The router assigns an initial sequence number to the neighboring station, and increases the sequence number every time it sends a message. The neighboring station sends back the received sequence number value. The sending value is used to compare the sent value with the value at the time of sending to ensure the correctness of the message.