Thanks to Kenny Barlee the Open5GS EPC MME now has the functionality to select which S-GW to send traffic to based on the Tracking Area Code of the eNodeB or the eNodeB ID.

This is a really useful Feature that allows you to break up your S-GW (And by extension P-GW) selection based on geographical areas.

This can be used to enable Local Breakout to a S/P-GW located at the same site as the tower, but controlled by a central MME / HSS.

After updating to the latest version the configuration is pretty straightforard,

P-GW Selection based on eNB ID

# o SGW selection by eNodeB ID (either single enb_id or multiple enb_ids, decimal or hex representation)
#
   selection_mode: enb_id
   gtpc:
     - addr: 127.0.2.3
       enb_id: [9413, 0x98765]

The above config will send any traffic from eNBs with the eNB ID 9413 (encoded as an intiger) or 0x98765 (Encoded as hex int equivilent 624485) to an S-GW at 127.0.2.3.

P-GW Selection based on TAC

# SGW selection by eNodeB TAC (either single TAC or multiple TACs)
#
selection_mode: tac
   gtpc:
     - addr: 127.0.2.2
       tac: [25000, 27000, 28000]

The above config will send any traffic from eNBs with TACs of 25000, 27000, 28000 to an S-GW at 127.0.2.2.