referring to external networking - L3 FDS/GBP architecture proposal - https://wiki.opnfv.org/display/fds/OpenStack-ODL-VPP+integration+design+and+architecture
there is a need to create SNAT API func. in HC.

SNAT API should be created to enable SNAT functionality of VPP to be configured using GBP
There should be support in VPP for SNAT configuration.
commands:
set interface snat set interface snat in <intfc> out <intfc> [del]
snat add address snat add addresses <ip4-range-start> [- <ip4-range-end>]
show snat show snat

it is already reported in VPP under VPP-231
for further questions, refer to Tomas Cechvala (tcechval@cisco.com) and Michal Cmarada (mcmarada@cisco.com) from GBP project