Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ????

I don't think there is an RFC that explicitly explains this, the reason it works is that if you take the address 127.1/24, the netmask specifies that the first 24 bits are the network address and the rest are the host address, the 127 falls within the network address part, setting the appropriate bits to one, and leaves all the other bits in the network part (even the unspecified ones) as zeros, since there is no third state that can represent the undefined value.

So, the way I understand it, it works something like this:

127.1 gets translated to binary and becomes 0111111100000001
The 24 bit netmask tells us that the host part is the last 8 bits, or 00000001
That leaves the other 24 bits for the network part, padded with zeros we get 011111110000000000000000
Stick these back together and you get 01111111000000000000000000000001
Split this long binary number into 4 bytes, and convert them back to decimal, and it leaves you with 127.0.0.1

Comment on Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ????

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Re: gethostbyname("1.1.1") returns 1.1.0.1 ???? by Abigail-II (Bishop) on Mar 07, 2003 at 00:00 UTC
I'm pretty sure that's not the reason. First, addresses like `127.1` work even if you do not give a a netmask. Secondly, the notation was used even before we had classless networks, and we were still dealing with A, B, C and D class networks. Note that many utilities also accept addresses in hex, octal, or even a combination of hex, octal and decimal: $ ping -c 1 0x42.047.54.0x1b # www.perlmonks.org PING 0x42.047.54.0x1b (66.39.54.27): 56 data bytes 64 bytes from 66.39.54.27: icmp_seq=0 ttl=244 time=114.3 ms --- 0x42.047.54.0x1b ping statistics --- 1 packets transmitted, 1 packets received, 0% packet loss round-trip min/avg/max = 114.3/114.3/114.3 ms $ [download] Abigail	[reply] [d/l] [select]

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Re: gethostbyname("1.1.1") returns 1.1.0.1 ????
by Abigail-II (Bishop) on Mar 07, 2003 at 00:00 UTC

127.1

Note that many utilities also accept addresses in hex, octal, or even a combination of hex, octal and decimal:

    $ ping -c 1 0x42.047.54.0x1b  # www.perlmonks.org
    PING 0x42.047.54.0x1b (66.39.54.27): 56 data bytes
    64 bytes from 66.39.54.27: icmp_seq=0 ttl=244 time=114.3 ms

    --- 0x42.047.54.0x1b ping statistics ---
    1 packets transmitted, 1 packets received, 0% packet loss
    round-trip min/avg/max = 114.3/114.3/114.3 ms
    $
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Abigail

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