[UNET] Optimal packetSize / fragmentSize ?

Hello.

I'm not a super engineer in network and i want to set the networkServer by my own to better control it (and also to learn about it ).

So i wanted to set the config NetworkServer and i found this :

ConnectionConfig config = new ConnectionConfig();
config.PacketSize = packetSize;
config.FragmentSize = fragmentSize;

My question is simple : What is the optimal Packet/Fragment Size for reducing lag ?

And the bonus question is : Why we have to configure both Client/Server when they need to have the same configuration ? (no ? i get errors if i don't do the same config )

 

So ?? no idea or just nothing to do of this ? x)