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I was reading an introduction to IPv6 which talks about the depletion of IPv4 addresses.

I came across the following line:

As noted in RFC 5735 a number of address blocks are reserved for users outside 'conventional' use in the public Internet as unicast identity tokens.

What are "Unicast Identity Tokens"? Googling it up didn't yield much results.

Also the same introduction shows the following figure shortly after:

IPv4 address distribution

What is the gray "Multicast" group? Is it related to the previous point?

  • May help if you provide the source. And no, multicast is not Unitas. – YLearn Dec 6 '17 at 10:07
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Feb 19 '18 at 20:18
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The cited RFC5735 doesn't contain the word "identity" nor the work "token", so it seems your source is wrong.

In this RFC you will found a pretty clear explanation of each reserverd IP address space, and a summary table:

4.  Summary Table

Address Block       Present Use                Reference
------------------------------------------------------------------
0.0.0.0/8           "This" Network             RFC 1122, Section 3.2.1.3
10.0.0.0/8          Private-Use Networks       RFC 1918
127.0.0.0/8         Loopback                   RFC 1122, Section 3.2.1.3
169.254.0.0/16      Link Local                 RFC 3927
172.16.0.0/12       Private-Use Networks       RFC 1918
192.0.0.0/24        IETF Protocol Assignments  RFC 5736
192.0.2.0/24        TEST-NET-1                 RFC 5737
192.88.99.0/24      6to4 Relay Anycast         RFC 3068
192.168.0.0/16      Private-Use Networks       RFC 1918
198.18.0.0/15       Network Interconnect
                    Device Benchmark Testing   RFC 2544
198.51.100.0/24     TEST-NET-2                 RFC 5737
203.0.113.0/24      TEST-NET-3                 RFC 5737
224.0.0.0/4         Multicast                  RFC 3171
240.0.0.0/4         Reserved for Future Use    RFC 1112, Section 4
255.255.255.255/32  Limited Broadcast          RFC 919, Section 7
                                               RFC 922, Section 7

There's nothing even remotely related to identity.

As for the grey area "Multicast" in you picture it is the line:

224.0.0.0/4 Multicast RFC 3171

in the table above.

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