The Hebrew University Magnes Press


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18 Chapter 1: Networking

by Kevin Schroeder
18 Chapter 1: Networking and Sockets At this point, you might be asking yourself, “ As a Web developer, why am I going through this in the fi rst place?” There are several reasons: ● Because you should. Many PHP developers just assume that the network is there without knowing the underlying concepts. Although it may not always be necessary to have that knowledge, it will make you more aware of network- related issues you may encounter. ● The security concept of Defense in Depth posits that a security implementation should have multiple layers. This design lets you add a networking component to your overall security implementation should you need it. ● You could provide diff erent content for people who are on a specifi c network ( e. g., a competitor). ● By understanding some of the basics of networking, you can build better, faster, more secure, more interesting network services. From Web services to your own binary protocols, an understanding of basic network concepts helps you to write better programs. Reserved IP Addresses Several reserved IP addresses are regulated by the IANA. These addresses will not be assigned to any given organization. Table 1.3 lists these IP addresses, with their respective CIDR address block and a brief description of their use. Table 1.3: CIDR address blocks CIDR address block Description 0.0.0.0/ 8 Current network; usually used to listen on all local interfaces. 10.0.0.0/ 8 Private class A network; you are free to use this address block internally in your organization. 14.0.0.0/ 8 Public data networks; this is a class A network that is used for transmission of public information. Some examples include telephone service connections and fi nancial transactions. 127.0.0.0/ 8 Loopback; your local host. 128.0.0.0/ 16 Reserved, but may have IP addresses granted to a Regional Internet Registry. 169.254.0.0/ 16 Link- Local; used for local data traffi c, such as on a wireless local network, between individuals on the same physical device. You may notice that if your Windows machine does not get an IP address from the DHCP, it defaults to having an IP address on this network.

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18 Chapter 1: Networking and Sockets At this point, you might be asking yourself, “ As a Web developer, why am I going through this in the fi rst place?” There are several reasons: ● Because you should. Many PHP developers just assume that the network is there without knowing the underlying concepts. Although it may not always be necessary to have that knowledge, it will make you more aware of network- related issues you may encounter. ● The security concept of Defense in Depth posits that a security implementation should have multiple layers. This design lets you add a networking component to your overall security implementation should you need it. ● You could provide diff erent content for people who are on a specifi c network ( e. g., a competitor). ● By understanding some of the basics of networking, you can build better, faster, more secure, more interesting network services. From Web services to your own binary protocols, an understanding of basic network concepts helps you to write better programs. Reserved IP Addresses Several reserved IP addresses are regulated by the IANA. These addresses will not be assigned to any given organization. Table 1.3 lists these IP addresses, with their respective CIDR address block and a brief description of their use. Table 1.3: CIDR address blocks CIDR address block Description 0.0.0.0/ 8 Current network; usually used to listen on all local interfaces. 10.0.0.0/ 8 Private class A network; you are free to use this address block internally in your organization. 14.0.0.0/ 8 Public data networks; this is a class A network that is used for transmission of public information. Some examples include telephone service connections and fi nancial transactions. 127.0.0.0/ 8 Loopback; your local host. 128.0.0.0/ 16 Reserved, but may have IP addresses granted to a Regional Internet Registry. 169.254.0.0/ 16 Link- Local; used for local data traffi c, such as on a wireless local network, between individuals on the same physical device. You may notice that if your Windows machine does not get an IP address from the DHCP, it defaults to having an IP address on this network.
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MC Press Online - 9781583470992


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