4 ms·

This will break code that uses (e.g.) 0.0.0.1 as a "fail address": $ telnet 0.0.0.1 22 Trying 0.0.0.1... telnet: Unable to connect to remote host:

by p1mrx 7y ago

This will break code that uses (e.g.) 0.0.0.1 as a "fail address": $ telnet 0.0.0.1 22 Trying 0.0.0.1... telnet: Unable to connect to remote host: Invalid argument It's nice because the connect() syscall fails immediately, instead of sending packets and waiting for a timeout. 0.0.0.0 is not a suitable replacement, because it's interpreted as 127.0.0.1: $ telnet 0.0.0.0 22 Trying 0.0.0.0... Connected to 0.0.0.0. Escape character is '^]'. SSH-2.0-OpenSSH_7.9p1 Debian-10 Doesn't the kernel have a policy of not breaking userspace, even if the behavior is undocumented?

zonidjan 7y ago
Why would code detect a failure and then use a fake address to cause an error, instead of just erroring?
- p1mrx 7y ago
  The address may not be controlled by the code in question. Think /etc/hosts, command line flags, and config files, where you want some condition to trigger an error.
herpderperator 7y ago
If you ask me, 0.0.0.0 should not be interpreted as 127.0.0.1. Yes, I know programs like ping interpret it this way as well. I just think it's ridiculous.
- silverwind 7y ago
  Agree that the bug is in userspace. Unless there is a RFC that says "0.0.0.0 shall be interpreted as 127.0.0.1", it's just super-weird that it even does that.
- p_l 7y ago
  So, some software actually parses 0/8 as localhost? This explains so many broken tutorials..
- IshKebab 7y ago
  The main use is to control which interfaces servers listen on. I.e. can you access them from other machines.
- unilynx 7y ago
  It makes sense if you compare it to how listening sockets work - if I listen on 127.0.0.1:80, I can connect to 127.0.0.1:80. if I listen to 0.0.0.0:80 (all ipv4 addresses), I can connect to 0.0.0.0:80 And as a bonus, I can just 'telnet 0 80' instead of having to type out 127.0.0.1
IshKebab 7y ago
It says 0.0.0.0 is still reserved, and I've never heard of software using 0.0.0.1 as a "fail address". Is it really common?
- p1mrx 7y ago
  I know I've used it myself, but from a sample size of one, I can't say whether http://www.hyrumslaw.com/ http://www.hyrumslaw.com/ or http://xkcd.com/1172/ http://xkcd.com/1172/ is more relevant.

by p1mrx 7y ago

zonidjan 7y ago

Why would code detect a failure and then use a fake address to cause an error, instead of just erroring?

p1mrx 7y ago
The address may not be controlled by the code in question. Think /etc/hosts, command line flags, and config files, where you want some condition to trigger an error.

herpderperator 7y ago

If you ask me, 0.0.0.0 should not be interpreted as 127.0.0.1. Yes, I know programs like ping interpret it this way as well. I just think it's ridiculous.

silverwind 7y ago
Agree that the bug is in userspace. Unless there is a RFC that says "0.0.0.0 shall be interpreted as 127.0.0.1", it's just super-weird that it even does that.
p_l 7y ago
So, some software actually parses 0/8 as localhost? This explains so many broken tutorials..
IshKebab 7y ago
The main use is to control which interfaces servers listen on. I.e. can you access them from other machines.
unilynx 7y ago
It makes sense if you compare it to how listening sockets work - if I listen on 127.0.0.1:80, I can connect to 127.0.0.1:80. if I listen to 0.0.0.0:80 (all ipv4 addresses), I can connect to 0.0.0.0:80 And as a bonus, I can just 'telnet 0 80' instead of having to type out 127.0.0.1

IshKebab 7y ago

It says 0.0.0.0 is still reserved, and I've never heard of software using 0.0.0.1 as a "fail address". Is it really common?

p1mrx 7y ago
I know I've used it myself, but from a sample size of one, I can't say whether http://www.hyrumslaw.com/ http://www.hyrumslaw.com/ or http://xkcd.com/1172/ http://xkcd.com/1172/ is more relevant.