by

.0 (dot zero) IP ?

Acest articol este mai vechi de 1 an. Anumite informații s-ar putea să nu mai fie de actualitate.


Am tot auzit despre „greșeala” celor de la RDS și anume alocarea de adrese IP ce se termină în .0 (punct zero).
Pentru cei mai puțin pregătiți în domeniu, citez:

Addresses ending in 0 or 255
Main article: IPv4 subnetting reference

It is a common misunderstanding that addresses ending with an octet of 0 or 255 can never be assigned to hosts. (See also Subnet – all zeros or all ones.) This is only true of networks with subnet masks of at least 24 bits — Class C networks in the old classful addressing scheme, or in CIDR, networks with masks of /24 to /32 (or 255.255.255.0–255.255.255.255).

In classful addressing (now obsolete with the advent of CIDR), there are only three possible subnet masks: Class A, 255.0.0.0 or /8; Class B, 255.255.0.0 or /16; and Class C, 255.255.255.0 or /24. For example, in the subnet 192.168.5.0/255.255.255.0 (or 192.168.5.0/24) the identifier 192.168.5.0 refers to the entire subnet, so it cannot also refer to an individual device in that subnet.

A broadcast address is an address that allows information to be sent to all machines on a given subnet, rather than a specific machine. Generally, the broadcast address is found by obtaining the bit complement of the subnet mask and performing a bitwise OR operation with the network identifier. In other words, the broadcast address is the last address in the range belonging to the subnet. In our example, the broadcast address would be 192.168.5.255, so to avoid confusion this address also cannot be assigned to a host. On a Class A, B, or C subnet, the broadcast address always ends in 255.

However, this does not mean that every addresses ending in 255 cannot be used as a host address. For example, in the case of a Class B subnet 192.168.0.0/255.255.0.0 (or 192.168.0.0/16), equivalent to the address range 192.168.0.0–192.168.255.255, the broadcast address is 192.168.255.255. However, one can assign 192.168.1.255, 192.168.2.255, etc. (though this can cause confusion). Also, 192.168.0.0 is the network identifier and so cannot be assigned[why?][citation needed], but 192.168.1.0, 192.168.2.0, etc. can be assigned (though this can also cause confusion).

With the advent of CIDR, broadcast addresses do not necessarily end with 255.

In general, the first and last addresses in a subnet are used as the network identifier and broadcast address, respectively. All other addresses in the subnet can be assigned to hosts on that subnet.

Citatul de mai sus este luat de la http://en.wikipedia.org/wiki/IPv4#Addresses_ending_in_0_or_255

Lasă un răspuns

Adresa ta de email nu va fi publicată. Câmpurile obligatorii sunt marcate cu *