Address mask requests

Address mask requests
8.2.5 This page will explain address mask request messages and how they are used.
When a network administrator uses the process of subnetting to divide a major IP address into multiple subnets, a new subnet mask is created. This new subnet mask is important to identify network, subnet, and host bits in an IP address. If a host does not know the subnet mask, it may send an address mask request to the local router. If the address of the router is known, this request may be sent directly to the router. Otherwise, the request will be broadcast. When the router receives the request, it will respond with an address mask reply. This address mask reply will identify the correct subnet mask. For example, assume that a host is located within a Class B network and has an IP address of 172.16.5.2. This host does not know the subnet mask so it broadcasts an address mask request:
Source address: 172.16.5.2
Destination address: 255.255.255.255
Protocol: ICMP = 1
Type: Address Mask Request = AM1
Code: 0
Mask: 255.255.255.0
This broadcast is received by 172.16.5.1, the local router. The router responds with the address mask reply:
Source address: 172.16.5.1
Destination address: 172.16.5.2
Protocol: ICMP = 1
Type: Address Mask Reply = AM2
Code: 0
Mask: 255.255.255.0
The frame format for the address mask request and reply is shown in Figure

. Figure

shows the descriptions for each field in the address mask request message. Note that the same frame format is used for both the address mask request and the reply. However, an ICMP type number of 17 is assigned to the request and 18 is assigned to the reply.
The next page will introduce the ICMP router discovery message.

Comments

OSI layers / Peer-to-peer communications / TCP/IP model

OSI layers 2.3.4 This page discusses the seven layers of the OSI model. The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. - Dividing the network into seven layers provides the following advantages: • It breaks network communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand. In the foll...

PC Basic...

• Backplane – A backplane is an electronic circuit board containing circuitry and sockets into which additional electronic devices on other circuit boards or cards can be plugged; in a computer, generally synonymous with or part of the motherboard. • Network interface card (NIC) – An expansion board inserted into a computer so that the computer can be connected to a network. • Video card – A board that plugs into a PC to give it display capabilities. • Audio card – An expansion board that enables a computer to manipulate and output sounds. • Parallel port – An interface capable of transferring more than one bit simultaneously that is used to connect external devices such as printers. • Serial port – An interface that can be used for serial communication in which only one bit is transmitted at a time. • Mouse port – A port used to connect a mouse to a PC. • USB port – A Universal Serial Bus connector. A USB port connects devices such as a mouse or printer to the computer ...

Windowing

Windowing 11.1.5 This page will explain how windows are used to transmit data. Data packets must be delivered to the recipient in the same order in which they were transmitted to have a reliable, connection-oriented data transfer. The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order. An easy solution is to have a recipient acknowledge the receipt of each packet before the next packet is sent. If a sender had to wait for an ACK after each packet was sent, throughput would be low. Therefore, most connection-oriented, reliable protocols allow multiple packets to be sent before an ACK is received. The time interval after the sender transmits a data packet and before the sender processes any ACKs is used to transmit more data. The number of data packets the sender can transmit before it receives an ACK is known as the window size, or window. TCP uses expectational ACKs. This means that the ACK number refers to the next packet that is...

CCNA :) Be a Good Network Administrator

Search This Blog