53 udp is standard port for dns. dnsmasq is the local dns-cache running on the nit for getting together the different dns servers from the different interfaces (resolv.confs in /tmp) when you changed the port to 55 your local dns (127.0.0.1) is likely unusable and you must have the providers dns server in /etc/resolv.conf instead of nameserver 127.0.0.1.