4 ms·

You shouldn't use loopback to block hostnames but instead use 0.0.0.0

by eterm 12y ago

MichaelCrawford 12y ago
I understand that 0.0.0.0 is the local subnet broadcast address. Is that really the case? I've puzzled over using 127.0.0.2. What I really want to get is an RST immediately upon sending a SYN.
middleclick 12y ago
Can you please explain why?
- userbinator 12y ago
  0.0.0.0 is a completely invalid destination IP, and any attempts to establish a connection to it will fail long before any packets are sent. 127.0.0.1 is still valid so you depend on the network stack to either receive a RST sent to itself, or time out. At least on Windows, the former is much faster to return with an error. It also avoids potential conflicts if you happen to need to run a server on port 80 for any reason.
  - MichaelCrawford 12y ago
    When I ping 0.0.0.0, I get replies from 69.41.141.1. I don't know but expect that's earthlink's router.
    - userbinator 12y ago
      That's odd... on Windows, pinging 0.0.0.0 results in "Destination specified is invalid." On *nix, the behaviour is slightly different and is supposed to ping localhost instead (confirmed on one of my Linux machines): http://unix.stackexchange.com/questions/99336/how-does-ping-zero-works http://unix.stackexchange.com/questions/99336/how-does-ping-...
      - MichaelCrawford 12y ago
        Do the RFCs have anything to say about 0.0.0.0? Perhaps it is left up to the implementation, in which case both Windows and *NIX would be, strictly speaking, correct.
  - seanp2k2 12y ago
    This isn't true on non-windows OSes, where 0.0.0.0 (or simply 0) means all interfaces, not nothing. ssh to a web server and do curl 0 ; it's a super-useful shortcut. Further reading: http://serverfault.com/questions/78048/whats-the-difference-between-ip-address-0-0-0-0-and-127-0-0- http://serverfault.com/questions/78048/whats-the-difference-... http://en.m.wikipedia.org/wiki/0.0.0.0 http://en.m.wikipedia.org/wiki/0.0.0.0
gizmo686 12y ago
When I ping 0.0.0.0, I get replies from 127.0.0.1 (running Ubuntu 14.04).

You shouldn't use loopback to block hostnames but instead use 0.0.0.0

by eterm 12y ago

You shouldn't use loopback to block hostnames but instead use 0.0.0.0

I understand that 0.0.0.0 is the local subnet broadcast address. Is that really the case? I've puzzled over using 127.0.0.2. What I really want to get is an RST immediately upon sending a SYN.

middleclick 12y ago

Can you please explain why?

userbinator 12y ago
0.0.0.0 is a completely invalid destination IP, and any attempts to establish a connection to it will fail long before any packets are sent. 127.0.0.1 is still valid so you depend on the network stack to either receive a RST sent to itself, or time out. At least on Windows, the former is much faster to return with an error. It also avoids potential conflicts if you happen to need to run a server on port 80 for any reason.
- MichaelCrawford 12y ago
  When I ping 0.0.0.0, I get replies from 69.41.141.1. I don't know but expect that's earthlink's router.
  - userbinator 12y ago
    That's odd... on Windows, pinging 0.0.0.0 results in "Destination specified is invalid." On *nix, the behaviour is slightly different and is supposed to ping localhost instead (confirmed on one of my Linux machines): http://unix.stackexchange.com/questions/99336/how-does-ping-zero-works http://unix.stackexchange.com/questions/99336/how-does-ping-...
    - MichaelCrawford 12y ago
      Do the RFCs have anything to say about 0.0.0.0? Perhaps it is left up to the implementation, in which case both Windows and *NIX would be, strictly speaking, correct.
- seanp2k2 12y ago
  This isn't true on non-windows OSes, where 0.0.0.0 (or simply 0) means all interfaces, not nothing. ssh to a web server and do curl 0 ; it's a super-useful shortcut. Further reading: http://serverfault.com/questions/78048/whats-the-difference-between-ip-address-0-0-0-0-and-127-0-0- http://serverfault.com/questions/78048/whats-the-difference-... http://en.m.wikipedia.org/wiki/0.0.0.0 http://en.m.wikipedia.org/wiki/0.0.0.0

gizmo686 12y ago

When I ping 0.0.0.0, I get replies from 127.0.0.1 (running Ubuntu 14.04).