RFC 1365 (rfc1365) - Page 2 of 6
An IP Address Extension Proposal
Alternative Format: Original Text Document
RFC 1365 An IP Address Proposal September 1992
Increasing the size of the IP address field to more than 32 bits
would solve the problem, but at the expense of making a new IP header
definition that would be incompatible with the existing base of IP
implementations. OSI based solutions such as using CLNP have been
proposed but would take time to implement.
2. Proposal for IP extension
The IP header format should not be modified to minimize the changes
necessary for supporting the address extensions that are proposed in
this RFC. Instead an "escape" mechanism can be used to specify larger
address. The IP header length field is 4 bits and this allows a
maximum of fifteen 32-bit words where each word is 4 octets. The
minimum size of the IP header without options is 5 words, which
leaves 10 words for options. One can reserve 6 words (24 octets) for
the normal options and leave the remaining (4 words or 16 octets) for
a new option type that specifies an extended address. The details of
this mechanism are discussed below.
Class E should be defined with the its five high order bits set to
11110. Its current definition is that four 1's in the most
significant bits represent a class E address.
A new class F is proposed with its six high order bits set to 111110.
The new class F address would be placed in the same locations that
are used for source and destination IP address in the IP header, but
would specify that part of the addressing information is in the
options part of the IP header. This is illustrated in the figure
below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver. | IHL | TOS | Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|1|1|1|0| Offset| Reserved | Source IP address part 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|1|1|1|0| Offset| Reserved | Destination IP address part 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Options :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: SADDR Code |Len adr. part 2| Source IP address part 2 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: DADDR Code |Len adr. part 2| Destination IP address part 2 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Data :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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