Reserved IP Addresses
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| Reserved IP Addresses A component of an IP address with a value all bits 0 or all bits 1 has a special meaning: |
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| • All bits 0: An address with all bits 0 in the host number portion is interpreted as this host (IP address with host address =0). |
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| All bits zero in the network number portion is this network (IP address with network address =0). |
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| When a host wants to communicate over a network but does not yet know the network IP address, it may send packets with network address=0. |
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| Other hosts on the network interpret the address as meaning this network. Their replies contain the fully qualified network address, which the sender records for future use. |
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| All bits 1: An address with all bits 1 is interpreted as all networks or all hosts. For example, the following means all hosts on network 128.2 (class B address): |
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| 128.2.255.255 |
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| This is called a directed broadcast address because it contains both a valid network address and a broadcast host address. |
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| • Loopback: The class A network 127.0.0.0 is defined as the loopback network. Addresses from that network are assigned to interfaces that process data within the local system. These loopback interfaces do not access a physical network. |