Refine FortiOS OSPF GR handling

Author: a-v-popov

docs/caveats.md

@@ -353,12 +353,6 @@ Device-specific parameters:
 * FortiOS accepts the graceful restart timers in the 1-3600 second range. A value of 0 (allowed by the _netlab_ schema) is rejected by the device during configuration deployment.
 * Enabling graceful restart on any BGP neighbor also enables the global FortiOS **graceful-restart** switch, which preserves the forwarding state across a routing restart. Advertising the capability without it would announce forwarding-state preservation the device does not deliver.
 
-OSPF graceful restart (**ospf.gr**):
-
-* FortiOS enables OSPF graceful restart with a single `set restart-mode graceful-restart` keyword in each of its two OSPF processes — `config router ospf` (OSPFv2) and `config router ospf6` (OSPFv3), which _netlab_ addresses as the IPv4 and IPv6 address families of its OSPF module. That one switch makes the device both a restarting router and a helper; the two roles cannot be configured independently.
-* Because the roles are coupled, _netlab_ rejects two combinations on FortiOS: enabling **ospf.gr.helper** without **ospf.gr.restart** (FortiOS cannot act as a helper without also promising to preserve its own forwarding state across a restart), and enabling **ospf.gr.restart** while explicitly disabling **ospf.gr.helper**. A node that enables **ospf.gr.restart** therefore also acts as a graceful-restart helper.
-* **ospf.gr.restart.grace_period** maps to the FortiOS **restart-period** keyword (range 1-3600 seconds, device default 120) — the grace period the restarting router advertises in its Grace-LSA (RFC 3623 for OSPFv2, RFC 5187 for OSPFv3). **ospf.gr.helper.grace_period** has no standard counterpart: those RFCs define only the restarting router's grace period, not a helper-side limit, so it is an FRR-specific extension (FRR's **supported-grace-time**) with nothing to map to on FortiOS, and it is not rendered.
-
 Device configuration:
 
 * Use a recent version of Ansible and **fortinet.fortios** Ansible Galaxy collection (version 2.3.6 or later)

netsim/devices/fortios.py

@@ -23,32 +23,38 @@ def check_bgp_gr_restart_time(node: Box) -> None:
 
 
 def check_ospf_gr(node: Box) -> None:
-  """
-  FortiOS drives OSPF graceful restart from a single 'set restart-mode graceful-restart'
-  keyword per address family. That switch makes the device both a restarting router and a
-  helper; the two roles cannot be configured independently. Reject the combinations the
-  device cannot honour, leaving the restart role (which a helper rides along with) to render.
-  """
   for o_data,_,vname in _routing.rp_data(node,'ospf'):
     gr = o_data.get('gr',None)
-    restart_on = isinstance(gr,dict) and 'restart' in gr             # restart role explicitly enabled
-    helper_on = isinstance(gr,dict) and 'helper' in gr               # helper role explicitly enabled
-    helper_off = removed_attributes(o_data,'gr.helper')              # helper role explicitly disabled
+    if not isinstance(gr,dict):
+      continue
+
+    restart_on = 'restart' in gr
+    helper_on = 'helper' in gr
+    helper_off = removed_attributes(o_data,'gr.helper')
     vrf_info = f' in VRF {vname}' if vname else ''
 
-    if helper_on and not restart_on:                                 # Helper without restart: FortiOS would
-      log.error(                                                     # ... have to make the restart promise too
+    # FortiOS has one OSPF GR switch. Restart implies helper on FortiOS,
+    # but helper-only input must not enable forwarding-state preservation.
+    if helper_on and not restart_on:
+      log.error(
         f'FortiOS cannot enable the OSPF graceful-restart helper role without restart '
         f'(set ospf.gr.restart) on node {node.name}{vrf_info}',
         log.IncorrectValue,
         'fortios')
-    elif restart_on and helper_off:                                  # Restart with helper explicitly off:
-      log.error(                                                     # ... the two roles share one switch
+    elif restart_on and helper_off:
+      log.error(
         f'FortiOS cannot enable OSPF graceful-restart restart while ospf.gr.helper is disabled '
         f'on node {node.name}{vrf_info}',
         log.IncorrectValue,
         'fortios')
 
+    helper_data = gr.get('helper',{})
+    if isinstance(helper_data,dict) and 'grace_period' in helper_data:
+      log.warning(
+        text=f'FortiOS cannot limit OSPF graceful-restart helper grace period on node {node.name}{vrf_info}',
+        flag='gr_helper_grace',
+        module='ospf')
+
 
 class FortiOS(_Quirks):
 

netsim/modules/ospf.yml

@@ -113,3 +113,4 @@ features:
 
 warnings:
   inactive: True
+  gr_helper_grace: True