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Chapter 2 User access administration
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Before you continue, familiarize yourself with the basic concepts of Internet
addressing protocols.
Three kinds of Internet addressing
There are three kinds of Internet addressing:
•
IP addresses are direct communications over the Internet to the appropriate
destinations. All connections on the Internet are made using IP addresses.
Each IP address consists of an actual IP address and a port number. The
format is nnn.nnn.nnn.nnn:#. You can use one to three digits between each
decimal point in the address (such as, 206.210.192.99). IP addresses and port
numbers are separated by a colon (:). For example, 198.67.8.99:80.
•
Host names are human readable versions of IP addresses, such as
nortelnetworks.com or instant.net. The list of allowed/denied host names
controls only the ability to look up the IP address associated with a host name.
For example, if you open a browser and type in “www.xyz.com”, the browser
first asks the DNS proxy to look up the address of that name. Instant Internet
then checks the access controls having to do with host names and decides
whether or not the site is allowable. The access controls therefore determine
whether or not a name can be resolved into an address.
•
Port numbers can be any number from 0 to 65535, where the first 1024 are
well-known port numbers that define specific tasks. For example, Web
browsing occurs on port number 80, file transfer protocol (ftp) uses ports 20
and 21, and simple mail transfer protocol (SMTP) uses port 25.
Access to ports can be connectionless (UDP) or connection-oriented (TCP).
Note:
If you allow access based on host names, you must also allow
access to their associated IP addresses. To allow access to one Web site
and dis-allow access to all others, allow all IP addresses but deny access
based on host name.
Note:
You can think of the IP address (or domain name) as the address of
an apartment building, with the port number functioning as an apartment
within the building.
Summary of Contents for 400
Page 16: ...16 Contents 300868 G ...
Page 22: ...22 Figures 300868 G ...
Page 24: ...24 Tables 300868 G ...
Page 92: ...92 Chapter 2 User access administration 300868 G ...
Page 114: ...114 Chapter 3 Internet activity logging 300868 G ...
Page 166: ...166 Chapter 5 Advanced IP configuration 300868 G ...
Page 200: ...200 Chapter 6 IP security and VPN 300868 G ...
Page 256: ...256 Chapter 8 Advanced communications configuration 300868 G ...
Page 302: ...302 Chapter 10 Instant Internet unit configuration support and diagnostics 300868 G ...
Page 314: ...314 Appendix A Troubleshooting and error messages 300868 G ...
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