Furuno recommends using Category 5e LAN Cables with Shielded Metal RJ45 Connectors. (Absolutely do not use any cables with the plastic RJ45 connectors). CAT5e cables are enhanced versions of Category 5 LAN Cables and adheres to more stringent standards.
Keep in mind that a Furuno Network must be capable of transmitting data at speeds of up to 1000 Mbps (1 Gigabit per second). Especially if you have several MFDs, DRS Radars, and Sounder Modules all connected within a network.
I found a good well-priced source for Cat6 shielded cables with high data rates. I bought several from them and the quality was very good. They come in many lengths as required.