ENVS 1000 Lecture Notes - Lecture 38: Web Server, Network Layer, Address Resolution Protocol
10 May 2018
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ENVS 1000 Lecture 38 Notes – Port Application
Introduction
• You are probably familiar with port number 80, which is commonly used for Web
services.
• The port numbers for some of the familiar applications.
• Port numbers can be modified by an application.
• A large number of user-defined port numbers are available for this purpose.
• To accommodate this option, the application of the sender can specify the port number
of the application to which the message is being sent.
• For example, if a user knows that the Web server being addressed is on port 8080,
instead of port 80 (a common trick used to hide a Web server from users who do not
have access privileges), she can specify the port number by appending it to the URL with
a colon thus: www.somewhere.org/hidden Server:8080.
• As noted previously, the application sends its message to the transport layer, together
with sending and receiving port addresses and sending and receiving IP addresses.
• The transport layer and network layers perform the tasks we described earlier.
• The port addresses will not be looked at again until the message reaches the transport
level at the receiver.
• The network layer uses IP addresses to forward datagrams to the receiving node.
• This is not the whole story, however, because the data link and physical layers require
physical addresses to identify the nodes to which they are attached.
• Physical addresses are associated with individual devices connected to a network.
• IP addresses are converted to physical addresses by an address resolution protocol at
the network layer.
• The details of this process are left
• Both physical and IP addresses are required because devices can be moved from one
network to another and because IP addresses can be assigned dynamically.
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