fix: derive per-node IOL app id so linked routers get distinct MACs

IOL derives interface MACs from its application ID. With a constant
local-app every node shared the same MACs, and linked routers dropped
each other's frames as MAC loops — ARP never resolved and pings were
100% lost even though the whole uBridge datapath was forwarding.

Derive local-app from the node UUID (stable across restarts, kept in
1..1022) and align remote-app with the netiomux convention CML uses
(1023). Verified end to end: two iol-xe nodes, Ethernet0/0 link,
ARP resolves both ways, ping 4/5 (first loss = ARP), graceful
stop/start keeps the NVRAM config.

docs/features/iol-runner-docker.md

@@ -137,7 +137,10 @@ diagnosing wiring issues).
   `GNS3_IOL_MEMORY` (default 2048 MB). Keep container memory at IOL memory
   + ~512 MB headroom or the OOM-killer will shoot the router.
 * **MAC addresses**: the `mac_address` template field and per-adapter custom
-  MACs are ignored — IOL derives its own scheme (`aabb.cc00.0XY0`).
+  MACs are ignored — IOL derives its own scheme from the node's application
+  ID (`aabb.cc{app}{iface}`), e.g. `aabb.cc03.0400`. The ID is derived from
+  the node UUID so linked routers always get distinct MACs (nodes sharing an
+  ID would silently drop each other's frames as MAC loops).
 * **Interface names are IOL-style `Ethernet0/0`**, not `GigabitEthernet0/0`
   (4 ports per unit, matching the adapter-count granularity) — startup
   configs addressing `GigabitEthernet…` are rejected by the parser.

gns3server/compute/docker/iol_docker_vm.py

@@ -29,9 +29,8 @@ netiomux exposes per-interface AF_UNIX datagram sockets in the container's
 ``/tmp`` (``s%02d.sock`` receive, ``c%02d.sock`` send — raw Ethernet frames),
 wired by the generic ``GNS3_UNIX_SOCKET_NIO`` capability of VendorDockerVM
 (uBridge reaches them through a per-node runtime directory bound at /tmp —
-see ``VendorDockerVM._unix_socket_host_dir``). Because the netio bus
+see ``VendorDockerVM._unix_socket_host_dir``). The local application ID is
-directory is private to the node, the application IDs are fixed constants
+derived from the node ID so that linked nodes get distinct MACs.
-with no cross-node collisions.
 
 This class is selected by the ``GNS3_IOL_RUNNER=1`` environment marker.
 """
@@ -194,8 +193,13 @@ class IOLDockerVM(VendorDockerVM):
             "memory": self._iol_memory,
             "num-eth": self.adapters * 4,  # every adapter is a 4-port unit
             "num-serial": 0,  # GNS3 docker adapters are ethernet-only
-            "local-app": 1,
+            # IOL derives interface MACs from the local application ID
-            "remote-app": 2,
+            # (aabb.cc00.0<app><iface>0); every node needs a distinct one or
+            # linked routers share MACs and drop each other's frames as loops.
+            # Derived from the node ID: stable across restarts, unique enough
+            # (CML allocates per-lab sequential IDs for the same reason).
+            "local-app": int(self.id.replace("-", ""), 16) % 1022 + 1,
+            "remote-app": 1023,  # netiomux's fake peer application ID
             "user-id": os.getuid(),
             "group-id": os.getgid(),
         }

tests/compute/docker/test_iol_docker_vm.py

@@ -261,14 +261,25 @@ async def test_start_writes_iol_config(compute_project, manager):
     assert config["binary"] == "/binary.iol"
     assert config["num-eth"] == 16  # 4 adapters, each a 4-port unit
     assert config["num-serial"] == 0
-    assert config["local-app"] == 1
+    assert config["local-app"] == int(vm.id.replace("-", ""), 16) % 1022 + 1
-    assert config["remote-app"] == 2
+    assert config["remote-app"] == 1023
     assert config["memory"] == 2048
     assert config["user-id"] == os.getuid()
     assert config["group-id"] == os.getgid()
     assert vm.status == "started"
 
 
+def test_local_app_is_distinct_per_node(compute_project, manager):
+    # IOL derives interface MACs from the app ID: two nodes sharing one would
+    # drop each other's frames as MAC loops, so IDs must differ per node.
+    vm1 = _make_vm(compute_project, manager)
+    vm2 = _make_vm(compute_project, manager)
+    id1 = int(vm1.id.replace("-", ""), 16) % 1022 + 1
+    id2 = int(vm2.id.replace("-", ""), 16) % 1022 + 1
+    assert id1 != id2
+    assert 1 <= id1 <= 1022 and 1 <= id2 <= 1022
+
+
 @pytest.mark.asyncio
 async def test_start_rewrites_config_on_adapter_change(compute_project, manager):