This file (/etc/resolv.conf) holds the config for the resolver in your dedicated box. Always make sure that you have the most recent nameservers listed in there without any lines reading “search domain.com” because that will slow things down.
It would be good practice to check with your dedicated hosting provider (datacenter) to always make sure they are up to date or if any nameservers go down. This is unlikely and rare, however, if you find your server downloading from remote servers quite slowly it is always something good to check.
Many other reasons can occur for slow servers including but not limited to: network issues, router problems (datacenter’s fault unless CoLo), massive traffic slowing down the pipe, a limited bandwidth pipe (10mbit or less with more traffic than that), DDOS and DOS attacks on the network. Always check the news or announcements section on your hosts’ website, blog, or forum and check your email for any items they may send regarding network status. Hope it helps.