After receiving its IP Address, a router will try to find its hostname.
On Ethernet networks, it could get the address of the DNS server via DHCP. If it gets that address then it will try to do a reverse DNS lookup to find its hostname. If the DNS server is not on the same subnet, the directly connected router should be configure with an ip helper-adddress.
Another option is for the router to request a specific file that contains IP to HOSTNAME mappings via TFTP. The address of the TFTP server could be sent to the router via DHCP Option 150. If not, the router will use the address 255.255.255.255 to reach any TFTP server on the subnet. If the TFTP server is on another subnet, the directly connected router should be configure with an ip helper-adddress.
The router will request the file network-config or cisconet.cfg from the TFTP server, in this order. This file should have a list of entries in the format: