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Used for link-local addresses [5] between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server 172.16.0.0/12 172.16.0.0–172.31.255.255
Multiple IPv6 addresses can be entered, as shown in the following example which uses a long command, not shown for brevity. The first two rows show that 3 of the entered addresses are in a /33 range, while 72 are in a /64. Blocking the /33 would affect 2G /64, that is, over 2 billion /64 allocations, but would block only 3 of the given addresses.
Ranges There are two types of IP ranges CIDR ranges, e.g. 123.123.123.0/24; Non-CIDR ranges; The latter are frequently found in the allocation of IP-address ranges by for instance a provider to a customers or DHCP allocated addresses for certain purposes, as can be found by querying the WHOIS dataase of a RIR.
Each / 8 block contains 256 3 = 2 24 = 16,777,216 addresses, which covers the whole range of the last three delimited segments of an IP address. This means that 256 /8 address blocks fit into the entire IPv4 space.
Shorter CIDR prefixes match more addresses, while longer prefixes match fewer. In the case of overlaid CIDR blocks, an address can match multiple CIDR prefixes of different lengths. CIDR is also used for IPv6 addresses and the syntax semantic is identical. The prefix length can range from 0 to 128, due to the larger number of bits in the address.
The Internet Engineering Task Force (IETF) has reserved the IPv4 address block 169.254.0.0 / 16 (169.254.0.0 – 169.254.255.255) for link-local addressing. [1] The entire range may be used for this purpose, except for the first 256 and last 256 addresses (169.254.0.0 / 24 and 169.254.255.0 / 24), which are reserved for future use and must not be selected by a host using this dynamic ...
In support of link-local multicasts which do not use IGMP, any IPv4 multicast address that falls within the *.0.0.0 / 24 and *.128.0.0 / 24 ranges will be broadcast to all ports on many Ethernet switches, even if IGMP snooping is enabled, so addresses within these ranges should be avoided on Ethernet networks where the functionality of IGMP ...
IP addresses in dot-decimal notation are also presented in CIDR notation, in which the IP address is suffixed with a slash and a number, used to specify the length of the associated routing prefix. For example, 127.0.0.1/8 specifies that the IP address has an eight-bit routing prefix, and therefore the subnet mask 255.0.0.0.