Tony Houghton wrote: > Bob Proulx wrote: > > Check /etc/resolv.conf for nameserver entries and modify or > > change the file as needed to say 'nameserver 0.0.0.0' (okay to use > > 'nameserver 127.0.0.1' with modern software too). See the wiki page > > for general information. > > I hadn't heard of 0.0.0.0 being used instead of 127.0.0.1. Is that > specific to resolv.conf?
The 0.0.0.0 address is interpreted by most TCP/IP OS implementations to mean the local host and will do the right thing. It can mostly be used interchangeably with 127.0.0.1 or any 127/8 address. The reason it became useful with the nameserver directive was that there was a bug in some Berkeley derived TCP/IP implementations that BIND would tickle. The resolver's connected datagram socket wouldn't rebind to a new local address and would "drag along" the previous 127.0.0.1 source address when switching to a new connection to the remote host. If the local name server was down the libc resolver would cycle to the next listed nameserver but end up sending a query with the bug of using the previous 127.0.0.1 address as the source address instead of the external IP address. In that case the remote nameserver would send a response back to themselves on the 127.0.0.1 address. Using 0.0.0.0 as the nameserver address avoided this bug when it was present on systems and also worked correctly on systems without the bug. Since it always worked everywhere the use of 0.0.0.0 was very common. This bug has probably been fixed for years now and so is unlikely to matter these days. But 0.0.0.0 always works and so why not use it? Bob
