А как же насчет руководства, приведенного выше?
В редакции 5.1
recv | xmit | via {ifX | if* | ipno | any}
Matches packets received, transmitted or going through, respec-
tively, the interface specified by exact name (ifX), by device
name (if*), by IP address, or through some interface.
В редакции 4.4
interface-spec
Some combinations of the following specifiers are allowed:
in Only match incoming packets.
out Only match outgoing packets.
via ifX Packet must be going through interface ifX.
via if* Packet must be going through interface ifX, where X is
any unit number.
via any Packet must be going through some interface.
via ipno Packet must be going through the interface having IP
address ipno.
Для указанного Вами есть другой случай