Hi all, Looks like I found issue in udhcpc6. from file d6_dhcpc.c: /* Default options */ IF_FEATURE_UDHCP_PORT(SERVER_PORT = 547;) IF_FEATURE_UDHCP_PORT(CLIENT_PORT = 546;) So if the ENABLE_FEATURE_UDHCP_PORT is disabled the SERVER_PORT and the CLIENT_PORT contain values related to IPv4 dhcp server/client. Thank you.