From a19a73543a56757ab81c63890e5ebc7e303f233b Mon Sep 17 00:00:00 2001
From: Roger Luethi <luethi@osism.tech>
Date: Mon, 20 Jul 2026 22:03:06 +0200
Subject: [PATCH] Gate SONiC EthernetN breakout on port topology

The loose SONiC-name breakout path treats any four consecutive
EthernetN interfaces at <=50G as a 4xNG breakout without consulting
the port_config topology. Unifying breakout mode selection widened
this path to also emit 4x10G (via BREAKOUT_MODE_BY_SPEED), so a switch
whose native low-speed ports happen to be named Ethernet0..3 is now
misdetected as a breakout -- e.g. AS5835-54T (native 10G) or
DellEMC-S5212f / AS7326-56X (native 25G) fabricate a 4x10G/4x25G cage
that does not exist.

Add a topology gate on this path: accept the group as a breakout only
when the port_config confirms a single multi-lane master (Ethernet
{base}) whose intermediate lanes Ethernet{base+1..base+3} are absent
-- they materialize only when the cage is actually broken out. Four
separate single-lane entries are native ports and are now skipped.
Unlike the EthX/Y/Z path, a bare EthernetN name carries no explicit
breakout signal, so the port_config is the only local evidence.

This is a necessary-not-sufficient negative filter: it removes the
known native-port false positives but cannot by itself prove breakout
intent. A follow-up will add an explicit per-port breakout_mode
declaration as the authoritative signal.

Add a regression test covering four native single-lane 25G ports.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Roger Luethi <luethi@osism.tech>
---
 osism/tasks/conductor/sonic/interface.py      | 27 ++++++++++++++++++
 .../sonic/test_breakout_detection.py          | 28 +++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/osism/tasks/conductor/sonic/interface.py b/osism/tasks/conductor/sonic/interface.py
index abb8c02eb..2ee32feaa 100644
--- a/osism/tasks/conductor/sonic/interface.py
+++ b/osism/tasks/conductor/sonic/interface.py
@@ -915,6 +915,33 @@ def detect_breakout_ports(device):
                 if len(sonic_breakout_group) == 4:
                     master_port = f"Ethernet{base_port}"
 
+                    # Topology gate: only treat consecutive EthernetN ports as a
+                    # breakout when the port_config confirms a single multi-lane
+                    # master whose intermediate lanes are absent — they only
+                    # materialize when the cage is broken out. Four separate
+                    # single-lane entries are native ports, not a breakout cage.
+                    # This prevents native low-speed switches (e.g. AS5835-54T
+                    # 10G, DellEMC-S5212f / AS7326-56X 25G) from being
+                    # misdetected as a 4xNG breakout. Unlike EthX/Y/Z, the bare
+                    # EthernetN name carries no explicit breakout signal, so the
+                    # port_config topology is the only local evidence available.
+                    master_cfg = port_config.get(master_port)
+                    if not master_cfg or "," not in master_cfg.get("lanes", ""):
+                        logger.debug(
+                            f"Skipping SONiC breakout for {master_port}: master "
+                            f"is not a multi-lane port in port_config (native port)"
+                        )
+                        continue
+                    if any(
+                        f"Ethernet{base_port + offset}" in port_config
+                        for offset in (1, 2, 3)
+                    ):
+                        logger.debug(
+                            f"Skipping SONiC breakout for {master_port}: "
+                            f"intermediate ports present in port_config (native ports)"
+                        )
+                        continue
+
                     # Determine breakout mode based on speed; the membership
                     # filter above (<= 50G) limits this path to 4x10G, 4x25G
                     # and 4x50G
diff --git a/tests/unit/tasks/conductor/sonic/test_breakout_detection.py b/tests/unit/tasks/conductor/sonic/test_breakout_detection.py
index b68b575bc..95198aac5 100644
--- a/tests/unit/tasks/conductor/sonic/test_breakout_detection.py
+++ b/tests/unit/tasks/conductor/sonic/test_breakout_detection.py
@@ -526,6 +526,34 @@ def test_detect_breakout_ports_sonic_standard_only_three_interfaces(
     }
 
 
+def test_detect_breakout_ports_sonic_standard_native_ports_not_breakout(
+    patch_breakout_helpers,
+):
+    # Four consecutive single-lane 25G ports that are each their own
+    # port_config entry are NATIVE ports, not a breakout cage, and must not be
+    # misdetected as a 4x25G breakout. A real breakout is a single multi-lane
+    # master with the intermediate lanes absent (they materialize only when the
+    # cage is broken out). This guards native low-speed switches such as
+    # DellEMC-S5212f / AS7326-56X (25G) and AS5835-54T (10G).
+    device = _make_sonic_device()
+    interfaces = [_make_iface(f"Ethernet{n}", speed=25_000_000) for n in range(4)]
+    port_config = {
+        f"Ethernet{n}": {
+            "lanes": str(29 + n),  # one lane each -> native ports
+            "alias": f"twentyfiveGigE1/{n + 1}",
+            "index": str(n + 1),
+            "speed": "25000",
+        }
+        for n in range(4)
+    }
+    patch_breakout_helpers(interfaces=interfaces, port_config=port_config)
+
+    assert detect_breakout_ports(device) == {
+        "breakout_cfgs": {},
+        "breakout_ports": {},
+    }
+
+
 def test_detect_breakout_ports_sonic_standard_speed_resolved_from_port_type(
     patch_breakout_helpers,
 ):