Hostname resolution in a machine with multiple running eth ports

Question

Consider a machine having 4 eth ports running on it. Then to which eth port's ipaddress will the hostname resolve to?

Kindly guide me to some documentation to support your answers so that I could use them as proof in my project.

Thanks

Answer 1

externally to whatever IN A entry you defined for the host name in its dns zone.

locally to whatever you want the hostname to resolve to. to see how the resolver works, check out /etc/host.conf. a default ubuntu host.conf is:

order hosts,bind
multi on

first line is the old style of saying "check /etc/hosts then query dns", second is the new style of saying the same thing.

suppose you have eth0:10.0.0.1, eth1:10.0.0.2, eth2:10.0.0.3, eth4:10.0.0.4 and a hostname of "phony" defined in /etc/hostname (talking ubuntu, other distros may use different config schemes here altho i doubt it)

you can have the following /etc/hosts entries:

10.0.0.1 phony 

then phony will resolve to 10.0.0.1 for local services if you have something like this in /etc/hosts:

127.0.0.1 phony

phony will resolve to 127.0.0.1

if you have no declaration of phony in /etc/hosts then resolver will query the dns caches defined in /etc/resolv.conf, using the "domain" and "search" setups to build a dns compliant record (host) name.

so if you want to control to what the hostname resolves to for your local services, define it in /etc/hosts.

quick note: the hostname is normally just a dns label (that is, no "."). the domain name for your machine is normally defined in /etc/domainname

Answer 2

You don't mention which brand of Linux you're using.

RedHat (and Centos, and perhaps even Fedora) uses the /etc/sysconfig/network file to determine the host's name. Then, using the host's name, it determines the IP address of the host using the normal naming system (as given in /etc/resolv.conf), which in practice means that you should have an IP-to-name mapping in /etc/hosts.

The IP addresses are associated to the NICs in /etc/sysconfig/network-scripts/ethX, where X is an integer (0, 1, 2, and 3 in your case).

See http://www.centos.org/docs/5/html/5.2/Deployment_Guide/s2-sysconfig-network.html and Ch03:_Linux_Networking">http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:Ch03:_Linux_Networking

...and http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-networkscripts.html