iptables -I INPUT -i eth1 -p udp --dport 137 --sport 137 -j DROP

tcpdump -e -nn -i eth1 dst port 137 and src port 137
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
17:24:47.706922 00:1b:fc:eb:16:1f > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.135.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
17:24:48.456179 00:1b:fc:eb:16:1f > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.135.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
17:24:48.626313 00:01:2e:1d:c6:28 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.162.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
17:24:49.206671 00:1b:fc:eb:16:1f > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.135.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
17:24:49.375986 00:01:2e:1d:c6:28 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.162.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
17:24:49.876572 00:25:22:b5:49:a8 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 92: 192.168.5.45.137 > 192.168.5.255.137: NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST