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, 2017 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, 2018 at 20:18

1 Answer 1


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
------------------------------------------------------------------           "This" Network             RFC 1122, Section          Private-Use Networks       RFC 1918         Loopback                   RFC 1122, Section      Link Local                 RFC 3927       Private-Use Networks       RFC 1918        IETF Protocol Assignments  RFC 5736        TEST-NET-1                 RFC 5737      6to4 Relay Anycast         RFC 3068      Private-Use Networks       RFC 1918       Network Interconnect
                    Device Benchmark Testing   RFC 2544     TEST-NET-2                 RFC 5737      TEST-NET-3                 RFC 5737         Multicast                  RFC 3171         Reserved for Future Use    RFC 1112, Section 4  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: Multicast RFC 3171

in the table above.


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