LW needs address filters which block RFC1918 and similar addresses, i.e. the address blocks 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8, and 224.0.0.0/3.

The reasons should be obvious -- the first three are not routed on the global internet, 127.0.0.1 connects LimeWire to itself, and multicast addresses are unuseable with TCP/IP.

Manually entering a RFC1918 address should work, but not the other two. Addresses from any of these blocks which are received from an external source (routers.gnutella.org, et al.) should be dropped unconditionally.