VETH1_ADDR
err = make_sockaddr(AF_INET, VETH1_ADDR, SERVER_PORT, &saddr, &saddr_len);
SYS(fail, "ip -net " NS1 " addr add " VETH1_ADDR "/24 dev " VETH1);
up = !SYS_NOFAIL("ip netns exec " NS0 " ping -c 1 -W 1 " VETH1_ADDR);