The "outbound-interface" filter
The outbound-interface filter applies only to SNAT rules. It specifies the outbound traffic flow to which NAT applies.
Filtering outbound traffic
The following example shows how to apply a SNAT rule, rule 20, to outbound traffic on the dp0p1p2 interface.
vyatta@vyatta# set service nat source rule 20 outbound-interface dp0p1p2