nameserver should be static

src/include/gpxe/dns.h

 	struct dns_rr_info_cname cname;
 };
 
-extern struct sockaddr_tcpip nameserver;
-
 #endif /* _GPXE_DNS_H */

src/net/udp/dns.c

  */
 
 /** The DNS server */
-struct sockaddr_tcpip nameserver = {
+static struct sockaddr_tcpip nameserver = {
 	.st_port = htons ( DNS_PORT ),
 };