Well-Known Ports

Transport Layer is the forth layer in #Open Systems Interconnection (OSI) Model. It has the same name under #Internet Protocol Suite (TCP/IP). Its main purpose is to transfer the chunk of data from Application Layer onto the network. Sometimes, it will cut down the sizes of the data and send them as several packets (its #Protocol Data Units (PDU)). Their header will identify the Well-Known Ports# or socket numbers of the sender and receiver.

Socket Programming aims to connect two computers or processes by specifying with socket, which is a pair of IPv4 Address# and port number#. By establishing a socket, both of them could communicate in duplex mode or both directions, in and out, using Internet Protocol Suite (TCP/IP)#. However, in socket programming, we usually define two entity: server and client. Server as the sender who send the messages, client as the receiver who receive and/or process the messages.

The managers issue GetRequest, GetNextRequest, and SetRequest messages to port# 161 which the agents should reply with GetResponse message to the same port. The managers listen to the port 162 in case there is a Trap message issued by the agents due to changes in Management Information Base (MIB) and underlying node.

RIP will periodically broadcast the router’s routing table to its neighbours’ #port 520 every 30 seconds (default). The RIP message is transferred using #User Datagram Protocol (UDP). There are two types of message: request message and response message. Request message is sent out on startup by RIP enable interface which requests all RIP enabled neighbours to send routing table to it. Response message on the other hand is the response to the request message, which sends the data containing routing table to the requesting interface.

Note: The backend’s service port is often used to connect to the 202201311634’s, specified by the name, port. See 202202181236.