Also, I've noticed that none of the tests included with libnice are hitting my stun server as well... I am setting NICE_STUN_SERVER and NICE_STUN_SERVER_PORT and I can echo those, and see they are correct... Further, I have utility "stunbdc" that is able to talk to my stun server... Here's the relevant part of an strace I did: socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 13 fcntl64(13, F_GETFD) = 0 fcntl64(13, F_SETFD, FD_CLOEXEC) = 0 fcntl64(13, F_GETFL) = 0x2 (flags O_RDWR) fcntl64(13, F_SETFL, O_RDWR|O_NONBLOCK) = 0 bind(13, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 getsockname(13, {sa_family=AF_INET, sin_port=htons(56963), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0 setsockopt(13, SOL_IP, IP_TOS, [0], 4) = 0 setsockopt(13, SOL_IPV6, 0x43 /* IPV6_??? */, [0], 4) = -1 ENOPROTOOPT (Protocol not available) mmap2(NULL, 143360, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb648f000 socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 14 fcntl64(14, F_GETFD) = 0 fcntl64(14, F_SETFD, FD_CLOEXEC) = 0 fcntl64(14, F_GETFL) = 0x2 (flags O_RDWR) fcntl64(14, F_SETFL, O_RDWR|O_NONBLOCK) = 0 bind(14, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 0 getsockname(14, {sa_family=AF_INET, sin_port=htons(36159), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0 setsockopt(14, SOL_IP, IP_TOS, [0], 4) = 0 setsockopt(14, SOL_IPV6, 0x43 /* IPV6_??? */, [0], 4) = -1 ENOPROTOOPT (Protocol not available) mmap2(NULL, 143360, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb646c000 open("/dev/urandom", O_RDONLY) = 15 fstat64(15, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 9), ...}) = 0 ioctl(15, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbf9b37e0) = -1 EINVAL (Invalid argument) mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb78c4000 read(15, ",\r\33\307\275\3659\205\233\267\24\231\210\362b\356&*\375Xs\236\251\10*\305\204!\300\3072;"..., 4096) = 4096 close(15) = 0 munmap(0xb78c4000, 4096) = 0 clock_gettime(CLOCK_MONOTONIC, {3880882, 819057133}) = 0 sendto(13, "\0\1\0\0\221\314\250g\225\317\3\3362n^\r\3=6\210", 20, 0, {sa_family=AF_INET, sin_port=htons(3478), sin_addr=inet_addr("97.74.202.52")}, 16) = -1 EINVAL (Invalid argument) Notice all the calls that are operating on file descriptor 13. It's returned at the top by a call to socket()... looks good... Eventually, setsockopt() with an IPV6 specific argument fails (don't know what that means)... but then at the bottom, a sendto() fails and sets errno to EINVAL... Any ideas? td