Adding new test for coverage of ipv6 dynamic NDP state transition

feature/interface/ip/otg_tests/ipv6_neighbor_state_test/README.md

@@ -0,0 +1,105 @@
+# RT-5.16: IPv6 Dynamic Neighbor Discovery (NDP) State Transitions
+
+## Summary
+
+Verify the dynamic IPv6 Neighbor Discovery (NDP) state transitions on the DUT.
+This includes verifying neighbor resolution, transitions to STALE state on inactivity, and recovery back to REACHABLE when traffic resumes.
+
+## Procedure
+
+*   Configure DUT port-1 with IPv6 address `2001:db8:1::1/64` and port-2 with `2001:db8:2::1/64`.
+*   Configure ATE port-1 with IPv6 address `2001:db8:1::2/64` and ATE port-2 with `2001:db8:2::2/64`.
+*   Enable IPv6 on both interfaces.
+
+### TC1: Initial Neighbor Discovery Resolution (REACHABLE State)
+*   Start continuous traffic flow from ATE port-2 to ATE port-1 (forwarded by the DUT).
+*   Verify that the neighbor entry for ATE port-1 (`2001:db8:1::2`) is resolved on the DUT.
+*   Verify that the neighbor attributes under `/interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state` match:
+    *   `ip`: `2001:db8:1::2`
+    *   `link-layer-address`: ATE port-1 MAC address
+    *   `origin`: `DYNAMIC`
+    *   `neighbor-state`: `REACHABLE`
+
+### TC2: Neighbor Inactivity and Transition to STALE
+*   Stop all traffic forwarding and interface packets.
+*   Wait for the neighbor entry to transition to `STALE` state (usually ~30s-60s on typical implementations).
+*   Query `/interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state/neighbor-state` until it shows `STALE`.
+*   Verify the neighbor attributes:
+    *   `neighbor-state`: `STALE`
+    *   `link-layer-address`: remains populated with ATE port-1 MAC address
+
+### TC3: Stale Neighbor Traffic Recovery (Transition to REACHABLE)
+*   Resume continuous traffic flow from ATE port-2 to ATE port-1.
+*   Ensure that the DUT sends packets to the stale neighbor `2001:db8:1::2`.
+*   Verify that the neighbor state transitions back to `REACHABLE` (may transiently go through `DELAY` or `PROBE` state).
+*   Verify that the packet loss at the ATE receiver is sub-second (minimal packet loss during NDP probe phase).
+*   Verify that the neighbor attributes are updated back to:
+    *   `neighbor-state`: `REACHABLE`
+
+## Canonical OC
+
+```json
+{
+  "interfaces": {
+    "interface": [
+      {
+        "name": "Ethernet1",
+        "config": {
+          "name": "Ethernet1"
+        },
+        "subinterfaces": {
+          "subinterface": [
+            {
+              "index": 0,
+              "config": {
+                "index": 0
+              },
+              "ipv6": {
+                "config": {
+                  "enabled": true
+                },
+                "addresses": {
+                  "address": [
+                    {
+                      "ip": "2001:db8:1::1",
+                      "config": {
+                        "ip": "2001:db8:1::1",
+                        "prefix-length": 64
+                      }
+                    }
+                  ]
+                }
+              }
+            }
+          ]
+        }
+      }
+    ]
+  }
+}
+```
+
+## OpenConfig Path and RPC Coverage
+
+The below yaml defines the OC paths and RPC intended to be covered by this test.
+
+```yaml
+paths:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/config/enabled:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/addresses/address/config/ip:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/addresses/address/config/prefix-length:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state/ip:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state/link-layer-address:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state/neighbor-state:
+  /interfaces/interface/subinterfaces/subinterface/ipv6/neighbors/neighbor/state/origin:
+
+rpcs:
+  gnmi:
+    gNMI.Get:
+    gNMI.Set:
+    gNMI.Subscribe:
+```
+
+## Minimum DUT Platform Requirement
+
+FFF

feature/interface/ip/otg_tests/ipv6_neighbor_state_test/metadata.textproto

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+# proto-file: github.com/openconfig/featureprofiles/proto/metadata.proto
+# proto-message: Metadata
+
+uuid: "307a9ab1-5617-49ad-9b89-b0906ed9a750"
+plan_id: "RT-5.16"
+description: "IPv6 Dynamic Neighbor Discovery (NDP) State Transitions"
+testbed: TESTBED_DUT_ATE_2LINKS
+

testregistry.textproto

@@ -1224,6 +1224,12 @@ test: {
   readme: "https://github.com/openconfig/featureprofiles/blob/main/feature/interface/lacp/otg_tests/lacp_fallback_test/README.md"
   exec: " "
 }
+test: {
+  id: "RT-5.16"
+  description: "IPv6 Dynamic Neighbor Discovery (NDP) State Transitions"
+  readme: "https://github.com/openconfig/featureprofiles/blob/main/feature/interface/ip/otg_tests/ipv6_neighbor_state_test/README.md"
+  exec: " "
+}
 test: {
   id: "RT-6.1"
   description: "Core LLDP TLV Population"