My router is flashed with dd-wrt which uses the dnsmaq daemon.
About dnsmasq?
dnsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server.
To flush out dns cache the dnsmasq daemon has to be restarted.
Login to the router terminal and run commands
# stopservice dnsmasq
# startservice dnsmasq
