Reserve the connection for local wallets
Bitcoin Core allows you to bind a separate listening socket with specific white listing properties. It has enhanced transaction relaying for use as a gateway and an immunity to banning for bad behavior. 

  -whitebind=&lt;addr&gt;
       Bind to given address and whitelist peers connecting to it. Use
       [host]:port notation for IPv6


This command can be used in conjunction with whiteconnections to reserve some of the maxconnections limit for connections to the whitelist socket. maxconnections=128 and whiteconnections=4 will use 8 for outgoing connections, allow a maximum of 116 incoming connections, and reserve 4 additional connections for incoming clients on the whitelisted port.

In this case you would bind the whitelist socket to an internal port, and then point LAN nodes to it. This is also useful for attaching axillary programs like P2Pool or the Bitcoin Relay Network.