According to everything I read, the entire 127.x.x.x subnet should loopback.

However, on my Mac, I can only ping

I know I've done this before (though possibly on another OS) and has come in very useful for developing multiple SSL sites locally and for tunneling remote services for access on a local IP (for example I could ssh into my MySQL server, and just port forward the standard port to the same port on my local machine but on while my local server ran at


Here is the short answer: sudo ifconfig lo0 alias 127.0.0.* up

Each alias must be added individually (sudo ifconfig lo0 alias up, sudo ifconfig lo0 alias up). It can be done manually for testing, or a subset or the complete list of the other 250 available numbers in that subnet can be made into StartupItems script that will do it automagically at boot time.

The long answer: According to RFC3330, - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host. This is ordinarily implemented using only for loopback, but no addresses within this block should ever appear on any network anywhere.

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    If only there was a way to make it work for 127.*.*.* – Matthew Schinckel Dec 12 '12 at 4:27
  • If this turns out to also work on CentOS, you sir are getting a bounty from me. – Parthian Shot Jul 18 '14 at 19:33
  • Actually, either way you get a bounty. Since it doesn't work for CentOS, I'll just ask and answer that question once I find out the answer. – Parthian Shot Jul 18 '14 at 19:42
  • How I set up 4 servers on port 8, using different loopback addresses on debian9 Gnu/Linux superuser.com/a/1255308/62123 – ctrl-alt-delor Oct 2 '17 at 8:31

For those interested, here is a little bash script that adds all the aliases for the IPs 127.0.0.*:

for ((i=2;i<256;i++))
    sudo ifconfig lo0 alias 127.0.0.$i up
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  • Am I reading this wrong? What you created looks like it does all the addresses from to If you change "sudo ifconfig lo0 alias 127.0.0.$i up" to "sudo ifconfig lo0 alias 127.$i.$i.$i up" that'll get you most of them right? However you would skip anything that is less than 2.. So maybe use a different variable for the other two octets? The highest IP address for loopback is – Everett Dec 18 '15 at 14:45
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    @Everett, you read this correctly, it only does the addresses 127.0.0.*. The reason I didn't cover the whole range is that it is actually quite slow to process even 255 addresses, so 255x255x255 would take way too long. – laurent Dec 18 '15 at 14:47
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    Thanks. I just wanted to make sure that the expectation was set, because someone will come on here and say, "Hey, it didn't work for" I wouldn't do that, but someone will... – Everett Dec 18 '15 at 14:49
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    Actually, @Everett's proposal wouldn't work either, since it would only enable adresses such as or, that is all those with the three last digits are equals. You would need three distinct loops to actually enable all IPs in the 127/8 block. Yet doing this would certainly not be a good idea: it is highly probable, given that each IPs has to be enabled separately, that there are some resources attached to each assigned IP; allocating approximately 17.7 millions IPs (that is 256^3) might turn out to have some significant consequences... – jwatkins May 16 '16 at 16:49
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    @jwatkins Bottom line: Enable them only if you need them, which is a rule of thumb for everything, really. – William T Froggard Dec 17 '16 at 3:20

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