The article Linux Firewall Tutorial: IPTables Tables, Chains, Rules Fundamentals define the
RETURN target value as follow:
RETURN – Firewall will stop executing the next set of rules in the current chain for this packet. The control will be returned to the calling chain.
I was discussing with a colleague on the effect of a such a target's value has the first rule of the first chain.
As there is no calling chain, what would happen to the packet? Would it be rejected or accepted?