Indicates the network role of a board.
Options:
1. cascade(1) -indicates the subtending side, which is used for subtending and capturing certain protocol packets
2. network(2) -indicates the network side, which is used for upstream transmission
3. user(3) -indicates the user side, which is used for creating the service port
4. extend(4) -indicates the extend side, which is used for connecting to the extended frame
5. invalid(255)-indicates the invalid value