It is sometimes natural to want to write rules such as this:

if eth0 {
  chain INPUT ACCEPT;
  chain OUTPUT ACCEPT;
}

However, ferm complains:

Error in ferm.conf line 1:
if <--
Chain must be specified

This requirement seems rather arbitrary; in fact it can be worked around
by adding a chain directive before the `if', but this causes warnings
when the chain is overridden within the block. It would seem to be much
better if ferm would check that a chain is specified only once the `;' is
seen.