nb: provide 'discard' value for nexthop

According to OVN v21.06.0 'discard' is a valid value for nexthop.

Closes-Bug: #1946092
Change-Id: I1eb4eebd70e65e3c45a631349f484ac215147809

ovsdbapp/constants.py

@@ -37,3 +37,5 @@ POLICY_ACTION_TYPES = (POLICY_ACTION_ALLOW,
 
 PROTO_TCP = 'tcp'
 PROTO_UDP = 'udp'
+
+ROUTE_DISCARD = "discard"

ovsdbapp/schema/ovn_northbound/commands.py

@@ -849,7 +849,8 @@ class LrRouteAddCommand(cmd.BaseCommand):
     def __init__(self, api, router, prefix, nexthop, port=None,
                  policy='dst-ip', may_exist=False):
         prefix = str(netaddr.IPNetwork(prefix))
-        nexthop = str(netaddr.IPAddress(nexthop))
+        if nexthop != const.ROUTE_DISCARD:
+            nexthop = str(netaddr.IPAddress(nexthop))
         super().__init__(api)
         self.router = router
         self.prefix = prefix

ovsdbapp/tests/functional/schema/ovn_northbound/test_impl_idl.py

@@ -768,6 +768,11 @@ class TestLogicalRouterOps(OvnNorthboundTest):
         self._lr_add_route(router_name)
         self._lr_add_route(router_name, may_exist=True)
 
+    def test_lr_route_add_discard(self):
+        self._lr_add_route(nexthop=const.ROUTE_DISCARD)
+        self.assertRaises(netaddr.AddrFormatError, self._lr_add_route,
+                          prefix='not-discard')
+
     def test_lr_route_del(self):
         prefix = "192.0.2.0/25"
         route = self._lr_add_route(prefix=prefix)

releasenotes/notes/ovn-support-discard-nexthop-cdb1d35aceaf4b63.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - |
+    Support the new "discard" static route nexthop type. It was added in OVN 21.06.