I sudgest adding a function to read the IP of the Clients

Changes needed:

EthernetClient.h

class EthernetClient : public Client {
public:
 virtual uint8_t remoteIP(uint8_t *buf); // Change
};

EthernetClient.cpp

uint8_t EthernetClient::remoteIP(uint8_t *buf) {
 if (_sock != MAX_SOCK_NUM)
 return W5100.readSnDIPR(_sock, buf);
 return 0;
}

It is a simple and usefull change in the library that can be used to retrive the IP address of a client connected to the EthernetServer.