address
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IPv6 addresses, being 128 bits long, need 32 characters to write in
the general case, if standard hex representation, is used, plus more
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... for any punctuation inserted (typically about another 7 characters,
or 39 characters total). This document specifies a more compact
representation of IPv6 addresses, which permits encoding in a mere 20
bytes.
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It is always necessary to be able to write in characters the form of
an address, though in actual use it is always carried in binary. For
IP version 4 (IP ...
... IP version 4 (IP Classic) the well known dotted quad format is used.
That is, 10.1.0.23 is one such address. Each decimal integer
represents a one octet of the 4 octet ...
... integer
represents a one octet of the 4 octet address, and consequently has a
value between 0 and 255 (inclusive). The written length of the
address ...
... address, and consequently has a
value between 0 and 255 (inclusive). The written length of the
address varies between 7 and 15 bytes.
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... 16 octets long [IPv6], if the old
standard form were to be used, addresses would be anywhere between 31
and 63 bytes, which is, of course, untenable.
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Because of that, IPv6 had chosen to represent addresses using hex
digits, and use only half as many punctuation characters, which will
mean addresses ...
... addresses using hex
digits, and use only half as many punctuation characters, which will
mean addresses of between 15 and 39 bytes, which is still quite long.
Further, in an attempt to save more bytes, a special format was
invented, in which a single run of zero octets can be dropped, the
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... two adjacent punctuation characters indicate this has happened, the
number of missing zeroes can be deduced from the fixed size of the
address.
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In most cases, using genuine IPv6 addresses, one may expect the
address as written to tend toward the upper limit of 39 octets, as
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... In most cases, using genuine IPv6 addresses, one may expect the
address as written to tend toward the upper limit of 39 octets, as
long strings of zeroes are likely to be rare, and most of the other
groups ...
... groups of 4 hex digits are likely to be longer than a single non-zero
digit (just as MAC addresses typically have digits spread throughout
their length).
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... This document specifies a new encoding, which can always represent
any IPv6 address in 20 octets. While longer than the shortest
possible representation of an IPv6 address ...
... IPv6 address in 20 octets. While longer than the shortest
possible representation of an IPv6 address, this is barely longer
than half the longest representation, and will typically be shorter
than the representation of most IPv6 addresses ...
... IPv6 address, this is barely longer
than half the longest representation, and will typically be shorter
than the representation of most IPv6 addresses.
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[AddrSpec] specifies that the preferred text representation of IPv6
addresses is in one of three conventional forms.
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... The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
hexadecimal values of the eight 16-bit pieces of the address.
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a saving of just 5 characters from this typical address form, and
still leaving 21 characters.
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In other cases the saving is more dramatic, in the extreme case, the
address:
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that is, the unspecified address, can be written as
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... IPv6 form with the old IPv4
form, and is intended mostly for transition, when IPv4 addresses are
embedded into IPv6 addresses. These can be considerably longer than
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... form, and is intended mostly for transition, when IPv4 addresses are
embedded into IPv6 addresses. These can be considerably longer than
the longest normal IPv6 representation, and will eventually be phased
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... 2^128 is 340282366920938463463374607431768211456. 85^20 is
387595310845143558731231784820556640625, and thus in 20 digits of
base 85 representation all possible 2^128 IPv6 addresses can clearly
be encoded.
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... On the other hand, 94^19 is just
30862366077815087592879016454695419904, also insufficient to encode
all 2^128 different IPv6 addresses, so 20 characters would be needed
even with base 94 encoding. As there are just 94 ASCII characters ...
... of the ASCII characters, enabling more characters to be retained for
other uses, eg, to delimit the address.
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'"' and "'", which allow the representation of IPv6 addresses to
be quoted in other environments where some of the characters in
the chosen character set ...
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',' to allow lists of IPv6 addresses to conveniently be written,
and '.' to allow an IPv6 address to end a sentence without
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... ',' to allow lists of IPv6 addresses to conveniently be written,
and '.' to allow an IPv6 address to end a sentence without
requiring it to be quoted.
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... IPv6 addresses can be written in standard CIDR
address/length notation, and ':' because that causes problems when
used in mail headers and URLs ...
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'[' and ']', so those can be used to delimit IPv6 addresses when
represented as text strings, as they often are for IPv4,
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... Converting an IPv6 address to base 85. ...
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For example, consider the address shown above
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Thus in base85 the address is:
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This procedure is trivially reversed to produce the binary form of
the address from textually encoded format.
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Apart from generally reducing the length of an IPv6 address when
encode in a textual format, this scheme also has the benefit of
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... encode in a textual format, this scheme also has the benefit of
returning IPv6 addresses to a fixed length representation, leading
zeroes are never omitted, thus removing the ugly and awkward variable
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It may be expected that future processors will address this defect,
quite possibly before any significant IPv6 deployment ...
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By encoding addresses in this form, it is less likely that a casual
observer will be able to immediately detect the binary form of the
address ...
... addresses in this form, it is less likely that a casual
observer will be able to immediately detect the binary form of the
address, and thus will find it harder to make immediate use of the
address. As IPv6 addresses ...
... address, and thus will find it harder to make immediate use of the
address. As IPv6 addresses are not intended to be learned by humans,
one reason for which being that they are expected to alter in
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... address, and thus will find it harder to make immediate use of the
address. As IPv6 addresses are not intended to be learned by humans,
one reason for which being that they are expected to alter in
comparatively short timespan, by human perception, the somewhat
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... one reason for which being that they are expected to alter in
comparatively short timespan, by human perception, the somewhat
challenging nature of the addresses is seen as a feature.
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Further, the appearance of the address, as if it may be random
gibberish in a compressed file, makes it much harder to detect by a
packet sniffer programmed to look for bypassing addresses ...
... address, as if it may be random
gibberish in a compressed file, makes it much harder to detect by a
packet sniffer programmed to look for bypassing addresses.
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... Author's Address ...