diff --git a/neutron_lib/api/definitions/vpn.py b/neutron_lib/api/definitions/vpn.py
index 3762b2dbd..08d18cb8c 100644
--- a/neutron_lib/api/definitions/vpn.py
+++ b/neutron_lib/api/definitions/vpn.py
@@ -121,9 +121,11 @@ VPN_SUPPORTED_AUTH_ALGORITHMS = [
 
 # VPN phase1 negotiation mode constants
 VPN_PHASE1_NEGOTIATION_MODE_MAIN = 'main'
+VPN_PHASE1_NEGOTIATION_MODE_AGGRESSIVE = 'aggressive'
 
 VPN_SUPPORTED_PHASE1_NEGOTIATION_MODES = [
     VPN_PHASE1_NEGOTIATION_MODE_MAIN,
+    VPN_PHASE1_NEGOTIATION_MODE_AGGRESSIVE,
 ]
 
 # The alias of the extension.