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A client I work for chose a 10.42.*.* subnet for some of their cloud work.

Here we see a ubuntu service starting on the 10.42.*.* subnet. Here is another.

Here we see the Docker scheduler Rancher has chosen 10.42.*.* as its default subnet.

Why not 10.32.*.*? Why not 10.11.*.*?

My question is: Is there anything special about the 10.42.*.* subnet?

Steven Lu
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Hawkeye
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    42 is the answer to the ultimate question of life, the unverse and everything, so when you're picking a random number between 0 and 255 for a subnet, it will inevitably be 42. – Mike Scott May 30 '17 at 05:28
  • Awesome. I'll pay that - how about the 10? – Hawkeye May 30 '17 at 05:49
  • Probably could recommend against using 42 because of likely 10.42.0.0/16 collision due to these other nets which may exist. – Steven Lu Dec 19 '19 at 03:37

1 Answers1

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The only thing special about the 10.42.x.y range is that is part of the 10.0.0.0/8 RFC 1918 IPv4 address ranges allocated for private internets.
These address ranges are not allocated to any specific organisation and anyone may use these addresses without prior approval for their own purposes.

For completeness: RFC 5735 lists all special purpose IPv4 address ranges:

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
Community
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HBruijn
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  • excuse me for off topic. is 1.0.0.0 special too? – Nick May 30 '17 at 06:51
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    @Nick, you can use whois to query information regarding IP-addresses. `1.0.0.0` is part of the range `1.0.0.0 - 1.0.0.255` and described as *"Research prefix for APNIC Labs"* so no more special than any other globally unique assigned ip-address. – HBruijn May 30 '17 at 06:54