Number overall forming a LAN (8)
I believe the answer is:
ethernet
'a lan' is the definition.
(ethernet is a kind of lan)
'number overall' is the wordplay.
'number' becomes 'ether' (anaesthetic, something which numbs).
'overall' becomes 'net' (I've seen this in other clues).
'ether'+'net'='ETHERNET'
'forming' is the link.
(Other definitions for ethernet that I've seen before include "Local area computer network" , "System connecting several computers" , "Network of a number of computers" , "Communication system" , "comms system" .)