Mikrotik device configured with multiple subnets / pools with firewall rules to tighten security between users.
Would like Skype traffic between (local) users to remain local ; at this stage an international supernode is used to route traffic.
Possible to keep traffic local with either firewall rule / local proxy?
Any help / advice will be appreciated.
Not mut knowledge about Skype here, but p2p connections should be direct (no in-the-middle node that traffic goes “through”).
Can your clients establish a tcp connection directly (traffic going only through your routers)? Probably Yes.
Try a tracert command. Post results here.
Regards
dot-bot 
Even if you close everything else at your gateway box,Skype will get through a squid proxy , if you need to stop it in a hurry,transparently proxy at your gateway and put in regex in squid.conf that will drop CONNECTS to decimal ips…this works but will break other stuff too,and is far from ideal