From 67ffecc7099df7cdf4068f9bd1e14ff93663855b Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Thu, 19 Feb 2026 11:51:29 -0500
Subject: [PATCH 01/16] begin

---
 ...2026-02-17_16-20_add_interface_fec_mode.py | 26 +++++++++++++++++++
 .../middlewared/api/v26_0_0/interface.py      | 14 ++++++++++
 .../plugins/interface/addresses.py            | 10 +++++++
 .../middlewared/plugins/network.py            |  7 +++++
 4 files changed, 57 insertions(+)
 create mode 100644 src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py

diff --git a/src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py b/src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py
new file mode 100644
index 0000000000000..b79fb4d8c817a
--- /dev/null
+++ b/src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py
@@ -0,0 +1,26 @@
+"""Add FEC mode to network interfaces.
+
+Revision ID: ad6bd79a37d7
+Revises: a8f5d9e2c1b7
+Create Date: 2026-02-17 16:20:00.000000+00:00
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'ad6bd79a37d7'
+down_revision = 'a8f5d9e2c1b7'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table('network_interfaces', schema=None) as batch_op:
+        batch_op.add_column(sa.Column('int_fec_mode', sa.String(length=10), nullable=True))
+
+
+def downgrade():
+    with op.batch_alter_table('network_interfaces', schema=None) as batch_op:
+        batch_op.drop_column('int_fec_mode')
diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index 78d57a97aa54b..f3d0dc9d01daa 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -117,6 +117,8 @@ class InterfaceEntryState(BaseModel):
     pcp: int | None = NotRequired
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] | None = NotRequired
+    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
 
 
 class InterfaceEntry(BaseModel):
@@ -140,6 +142,8 @@ class InterfaceEntry(BaseModel):
     """Human-readable description of the interface."""
     mtu: int | None
     """Maximum transmission unit size for the interface."""
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] = NotRequired
+    """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
     vlan_tag: int | None = NotRequired
@@ -291,6 +295,16 @@ class InterfaceServicesRestartedOnSyncItem(BaseModel):
 
 class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     type: Excluded = excluded_field()
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]
+    """
+    Forward Error Correction (FEC) mode. Only valid for physical interfaces.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
 
 
 # -------------------   Args and Results   ------------------- #
diff --git a/src/middlewared/middlewared/plugins/interface/addresses.py b/src/middlewared/middlewared/plugins/interface/addresses.py
index 30e3aef819c29..97ab97e790e79 100644
--- a/src/middlewared/middlewared/plugins/interface/addresses.py
+++ b/src/middlewared/middlewared/plugins/interface/addresses.py
@@ -7,6 +7,7 @@
 from truenas_pynetif.address.constants import AddressFamily, IFFlags
 from truenas_pynetif.address.get_ipaddresses import get_link_addresses
 from truenas_pynetif.address.link import set_link_alias, set_link_mtu, set_link_up
+from truenas_pynetif.ethtool import DeviceNotFound, get_ethtool, OperationNotSupported
 from truenas_pynetif.netlink import AddressDoesNotExist, AddressInfo, LinkInfo
 
 from middlewared.plugins.interface.dhcp import dhcp_leases, dhcp_status, dhcp_stop
@@ -204,6 +205,15 @@ def configure_addresses_impl(
         elif link.mtu != 1500:
             set_link_mtu(sock, 1500, index=link_index)
 
+    # Apply FEC mode (physical interfaces only; virtual interfaces never have int_fec_mode set)
+    if fec_mode := data.get("int_fec_mode"):
+        try:
+            get_ethtool().set_fec(name, fec_mode)
+        except (OperationNotSupported, DeviceNotFound):
+            pass
+        except Exception:
+            ctx.logger.warning("Failed to set FEC mode on %s", name, exc_info=True)
+
     # Set interface description
     if data["int_name"]:
         try:
diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 9071f997cc199..7a6b1e69ac2a3 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -81,6 +81,7 @@ class NetworkInterfaceModel(sa.Model):
     int_critical = sa.Column(sa.Boolean(), default=False)
     int_group = sa.Column(sa.Integer(), nullable=True)
     int_mtu = sa.Column(sa.Integer(), nullable=True)
+    int_fec_mode = sa.Column(sa.String(10), nullable=True)
 
 
 class NetworkInterfaceLinkAddressModel(sa.Model):
@@ -254,6 +255,9 @@ def iface_extend(self, iface_state, configs, ha_hardware, fake=False):
             'description': config['int_name'],
             'mtu': config['int_mtu'],
         })
+        if itype == InterfaceType.PHYSICAL:
+            if fec_mode := config.get('int_fec_mode'):
+                iface['fec_mode'] = fec_mode
 
         if ha_hardware:
             info = ('INET', 32) if config['int_version'] == 4 else ('INET6', 128)
@@ -1088,6 +1092,7 @@ async def __convert_interface_datastore(self, data):
             'critical': data.get('failover_critical') or False,
             'group': data.get('failover_group'),
             'mtu': data.get('mtu') or None,
+            'fec_mode': data.get('fec_mode'),
         }
 
     async def __create_interface_datastore(self, data, attrs):
@@ -1221,6 +1226,8 @@ async def do_update(self, audit_callback, oid, data):
         )
         if await self.middleware.call('failover.licensed') and (new.get('ipv4_dhcp') or new.get('ipv6_auto')):
             verrors.add('interface_update.dhcp', 'Enabling DHCPv4/v6 on HA systems is unsupported.')
+        if 'fec_mode' in data and new['type'] != 'PHYSICAL':
+            verrors.add('interface.update.fec_mode', 'FEC mode can only be set on physical interfaces.')
 
         verrors.check()
 

From d16888374ed500ee562e9b625ac3ff3cd00f7206 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Thu, 19 Feb 2026 14:31:26 -0500
Subject: [PATCH 02/16] draft

---
 .../middlewared/api/v26_0_0/interface.py      | 13 +++++++++-
 .../middlewared/plugins/network.py            | 24 +++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index f3d0dc9d01daa..01038e96eb692 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -9,7 +9,8 @@
 
 
 __all__ = [
-    "InterfaceEntry", "InterfaceBridgeMembersChoicesArgs", "InterfaceBridgeMembersChoicesResult",
+    "InterfaceEntry", "InterfaceAvailableFecModesArgs", "InterfaceAvailableFecModesResult",
+    "InterfaceBridgeMembersChoicesArgs", "InterfaceBridgeMembersChoicesResult",
     "InterfaceCancelRollbackArgs", "InterfaceCancelRollbackResult", "InterfaceCheckinArgs", "InterfaceCheckinResult",
     "InterfaceCheckinWaitingArgs", "InterfaceCheckinWaitingResult", "InterfaceChoicesArgs", "InterfaceChoicesResult",
     "InterfaceCommitArgs", "InterfaceCommitResult", "InterfaceCreateArgs", "InterfaceCreateResult",
@@ -535,3 +536,13 @@ class InterfaceXmitHashPolicyChoicesResult(BaseModel):
     """Use MAC and IP addresses for traffic distribution across bond members."""
     LAYER3_4: Literal["LAYER3+4"] = Field(alias="LAYER3+4")
     """Use MAC, IP, and TCP/UDP port information for traffic distribution across bond members."""
+
+
+class InterfaceAvailableFecModesArgs(BaseModel):
+    id: str
+    """ID of the interface to query for supported FEC modes."""
+
+
+class InterfaceAvailableFecModesResult(BaseModel):
+    result: list[Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]]
+    """List of FEC modes supported by the interface. Empty list if FEC is not supported."""
diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 7a6b1e69ac2a3..6f722891efb63 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -7,7 +7,8 @@
 from middlewared.api import api_method
 from middlewared.plugins.interface.dhcp import dhcp_start
 from middlewared.api.current import (
-    InterfaceEntry, InterfaceBridgeMembersChoicesArgs, InterfaceBridgeMembersChoicesResult,
+    InterfaceEntry, InterfaceAvailableFecModesArgs, InterfaceAvailableFecModesResult,
+    InterfaceBridgeMembersChoicesArgs, InterfaceBridgeMembersChoicesResult,
     InterfaceCancelRollbackArgs, InterfaceCancelRollbackResult, InterfaceCheckinArgs, InterfaceCheckinResult,
     InterfaceCheckinWaitingArgs, InterfaceCheckinWaitingResult, InterfaceChoicesArgs, InterfaceChoicesResult,
     InterfaceCommitArgs, InterfaceCommitResult, InterfaceCreateArgs, InterfaceCreateResult,
@@ -32,6 +33,7 @@
 from middlewared.utils.filter_list import filter_list
 from truenas_pynetif.address.constants import AddressFamily
 from truenas_pynetif.address.netlink import get_addresses, get_default_route, netlink_route
+from truenas_pynetif.ethtool import get_ethtool
 from truenas_pynetif.interface import CLONED_PREFIXES
 from truenas_pynetif.interface_state import list_interface_states
 from truenas_pynetif.utils import INTERNAL_INTERFACES
@@ -1227,7 +1229,11 @@ async def do_update(self, audit_callback, oid, data):
         if await self.middleware.call('failover.licensed') and (new.get('ipv4_dhcp') or new.get('ipv6_auto')):
             verrors.add('interface_update.dhcp', 'Enabling DHCPv4/v6 on HA systems is unsupported.')
         if 'fec_mode' in data and new['type'] != 'PHYSICAL':
-            verrors.add('interface.update.fec_mode', 'FEC mode can only be set on physical interfaces.')
+            verrors.add('interface_update.fec_mode', 'FEC mode can only be set on physical interfaces.')
+        elif 'fec_mode' in data:
+            available = await self.middleware.call('interface.available_fec_modes', oid)
+            if available and data['fec_mode'] not in available:
+                verrors.add('interface_update.fec_mode', f'Unsupported FEC mode. Available: {available}')
 
         verrors.check()
 
@@ -1472,6 +1478,20 @@ async def lacpdu_rate_choices(self):
         """
         return {i.value: i.value for i in LacpduRateChoices}
 
+    @api_method(InterfaceAvailableFecModesArgs, InterfaceAvailableFecModesResult, roles=['NETWORK_INTERFACE_READ'])
+    async def available_fec_modes(self, id_):
+        """
+        Returns FEC modes supported by physical interface `id`.
+
+        Returns an empty list for non-physical interfaces or interfaces without FEC support.
+        """
+        iface = await self.get_instance(id_)
+        if iface['type'] != 'PHYSICAL':
+            return []
+        return await self.middleware.run_in_thread(
+            lambda: get_ethtool().get_fec_modes(iface['name'])
+        )
+
     @api_method(InterfaceChoicesArgs, InterfaceChoicesResult, roles=['NETWORK_INTERFACE_READ'])
     async def choices(self, options):
         """

From 487333c56bf1e83a61bc804e41ddd100a67e1070 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Thu, 19 Feb 2026 14:52:48 -0500
Subject: [PATCH 03/16] touch up

---
 .../middlewared/api/v26_0_0/interface.py      |  3 ++-
 .../middlewared/plugins/network.py            | 22 +++++++++++--------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index 01038e96eb692..941251a494357 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -2,6 +2,7 @@
 
 from pydantic import Field
 
+from truenas_pynetif.ethtool import FecModeName
 from middlewared.api.base import (
     BaseModel, IPv4Address, UniqueList, IPvAnyAddress, Excluded, excluded_field, ForUpdateMetaclass,
     single_argument_args, single_argument_result, NotRequired, NonEmptyString,
@@ -544,5 +545,5 @@ class InterfaceAvailableFecModesArgs(BaseModel):
 
 
 class InterfaceAvailableFecModesResult(BaseModel):
-    result: list[Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]]
+    result: list[FecModeName]
     """List of FEC modes supported by the interface. Empty list if FEC is not supported."""
diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 6f722891efb63..94f16624a784b 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -1228,12 +1228,18 @@ async def do_update(self, audit_callback, oid, data):
         )
         if await self.middleware.call('failover.licensed') and (new.get('ipv4_dhcp') or new.get('ipv6_auto')):
             verrors.add('interface_update.dhcp', 'Enabling DHCPv4/v6 on HA systems is unsupported.')
-        if 'fec_mode' in data and new['type'] != 'PHYSICAL':
-            verrors.add('interface_update.fec_mode', 'FEC mode can only be set on physical interfaces.')
-        elif 'fec_mode' in data:
-            available = await self.middleware.call('interface.available_fec_modes', oid)
-            if available and data['fec_mode'] not in available:
-                verrors.add('interface_update.fec_mode', f'Unsupported FEC mode. Available: {available}')
+        if 'fec_mode' in data:
+            if new['type'] == 'PHYSICAL':
+                if available := await self.available_fec_modes(oid):
+                    if data['fec_mode'] not in available:
+                        verrors.add(
+                            'interface_update.fec_mode',
+                            f'Unsupported FEC mode. Available: {", ".join(available)}'
+                        )
+                else:
+                    verrors.add('interface_update.fec_mode', 'This interface does not support FEC mode configuration.')
+            else:
+                verrors.add('interface_update.fec_mode', 'FEC mode can only be set on physical interfaces.')
 
         verrors.check()
 
@@ -1488,9 +1494,7 @@ async def available_fec_modes(self, id_):
         iface = await self.get_instance(id_)
         if iface['type'] != 'PHYSICAL':
             return []
-        return await self.middleware.run_in_thread(
-            lambda: get_ethtool().get_fec_modes(iface['name'])
-        )
+        return await self.middleware.run_in_thread(get_ethtool().get_fec_modes, iface['name'])
 
     @api_method(InterfaceChoicesArgs, InterfaceChoicesResult, roles=['NETWORK_INTERFACE_READ'])
     async def choices(self, options):

From cb2cfcbea07987d48f55a0c59a5e869b90e5c6d1 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Fri, 20 Feb 2026 10:00:37 -0500
Subject: [PATCH 04/16] remove unnecessary get_instance call

---
 src/middlewared/middlewared/plugins/network.py | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 94f16624a784b..36d7fb076033d 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -1487,14 +1487,11 @@ async def lacpdu_rate_choices(self):
     @api_method(InterfaceAvailableFecModesArgs, InterfaceAvailableFecModesResult, roles=['NETWORK_INTERFACE_READ'])
     async def available_fec_modes(self, id_):
         """
-        Returns FEC modes supported by physical interface `id`.
+        Returns FEC modes supported by interface `id`.
 
-        Returns an empty list for non-physical interfaces or interfaces without FEC support.
+        Returns an empty list if the interface does not exist or does not support FEC.
         """
-        iface = await self.get_instance(id_)
-        if iface['type'] != 'PHYSICAL':
-            return []
-        return await self.middleware.run_in_thread(get_ethtool().get_fec_modes, iface['name'])
+        return await self.middleware.run_in_thread(get_ethtool().get_fec_modes, id_)
 
     @api_method(InterfaceChoicesArgs, InterfaceChoicesResult, roles=['NETWORK_INTERFACE_READ'])
     async def choices(self, options):

From 0cff75554c5e7967e5e462f70d135175f88875f3 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Wed, 11 Mar 2026 14:35:07 -0400
Subject: [PATCH 05/16] 27 api

---
 .../middlewared/api/v27_0_0/interface.py      | 27 ++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index 78d57a97aa54b..e0aa5fa49cb5b 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -2,6 +2,7 @@
 
 from pydantic import Field
 
+from truenas_pynetif.ethtool import FecModeName
 from middlewared.api.base import (
     BaseModel, IPv4Address, UniqueList, IPvAnyAddress, Excluded, excluded_field, ForUpdateMetaclass,
     single_argument_args, single_argument_result, NotRequired, NonEmptyString,
@@ -9,7 +10,8 @@
 
 
 __all__ = [
-    "InterfaceEntry", "InterfaceBridgeMembersChoicesArgs", "InterfaceBridgeMembersChoicesResult",
+    "InterfaceEntry", "InterfaceAvailableFecModesArgs", "InterfaceAvailableFecModesResult",
+    "InterfaceBridgeMembersChoicesArgs", "InterfaceBridgeMembersChoicesResult",
     "InterfaceCancelRollbackArgs", "InterfaceCancelRollbackResult", "InterfaceCheckinArgs", "InterfaceCheckinResult",
     "InterfaceCheckinWaitingArgs", "InterfaceCheckinWaitingResult", "InterfaceChoicesArgs", "InterfaceChoicesResult",
     "InterfaceCommitArgs", "InterfaceCommitResult", "InterfaceCreateArgs", "InterfaceCreateResult",
@@ -117,6 +119,8 @@ class InterfaceEntryState(BaseModel):
     pcp: int | None = NotRequired
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] | None = NotRequired
+    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
 
 
 class InterfaceEntry(BaseModel):
@@ -140,6 +144,8 @@ class InterfaceEntry(BaseModel):
     """Human-readable description of the interface."""
     mtu: int | None
     """Maximum transmission unit size for the interface."""
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] = NotRequired
+    """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
     vlan_tag: int | None = NotRequired
@@ -291,6 +297,15 @@ class InterfaceServicesRestartedOnSyncItem(BaseModel):
 
 class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     type: Excluded = excluded_field()
+    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]
+    """
+    Forward Error Correction (FEC) mode. Only valid for physical interfaces.
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
 
 
 # -------------------   Args and Results   ------------------- #
@@ -521,3 +536,13 @@ class InterfaceXmitHashPolicyChoicesResult(BaseModel):
     """Use MAC and IP addresses for traffic distribution across bond members."""
     LAYER3_4: Literal["LAYER3+4"] = Field(alias="LAYER3+4")
     """Use MAC, IP, and TCP/UDP port information for traffic distribution across bond members."""
+
+
+class InterfaceAvailableFecModesArgs(BaseModel):
+    id: str
+    """ID of the interface to query for supported FEC modes."""
+
+
+class InterfaceAvailableFecModesResult(BaseModel):
+    result: list[FecModeName]
+    """List of FEC modes supported by the interface. Empty list if FEC is not supported."""

From b91c4e4ccd54cd2370a44b57933eeb29d9a226a3 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Wed, 11 Mar 2026 14:46:23 -0400
Subject: [PATCH 06/16] update migration

---
 ...fec_mode.py => 2026-03-11_18-44_add_interface_fec_mode.py} | 4 ++--
 .../alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)
 rename src/middlewared/middlewared/alembic/versions/26.0/{2026-02-17_16-20_add_interface_fec_mode.py => 2026-03-11_18-44_add_interface_fec_mode.py} (91%)

diff --git a/src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py b/src/middlewared/middlewared/alembic/versions/26.0/2026-03-11_18-44_add_interface_fec_mode.py
similarity index 91%
rename from src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py
rename to src/middlewared/middlewared/alembic/versions/26.0/2026-03-11_18-44_add_interface_fec_mode.py
index b79fb4d8c817a..0e39b2337649a 100644
--- a/src/middlewared/middlewared/alembic/versions/26.0/2026-02-17_16-20_add_interface_fec_mode.py
+++ b/src/middlewared/middlewared/alembic/versions/26.0/2026-03-11_18-44_add_interface_fec_mode.py
@@ -1,7 +1,7 @@
 """Add FEC mode to network interfaces.
 
 Revision ID: ad6bd79a37d7
-Revises: a8f5d9e2c1b7
+Revises: f3b4b0f4b0cf
 Create Date: 2026-02-17 16:20:00.000000+00:00
 
 """
@@ -11,7 +11,7 @@
 
 # revision identifiers, used by Alembic.
 revision = 'ad6bd79a37d7'
-down_revision = 'a8f5d9e2c1b7'
+down_revision = 'f3b4b0f4b0cf'
 branch_labels = None
 depends_on = None
 
diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
index af5f48ea5fed8..eddd9c5310d93 100644
--- a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
@@ -1,7 +1,7 @@
 """Remove ScrubNotStarted alerts
 
 Revision ID: 3fc58b28ce77
-Revises: f3b4b0f4b0cf
+Revises: ad6bd79a37d7
 Create Date: 2026-03-09 19:16:31.067201+00:00
 
 """
@@ -11,7 +11,7 @@
 
 # revision identifiers, used by Alembic.
 revision = '3fc58b28ce77'
-down_revision = 'f3b4b0f4b0cf'
+down_revision = 'ad6bd79a37d7'
 branch_labels = None
 depends_on = None
 

From eb7a4a66615daf42f8fcebe9a4dfade09c0bedca Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Wed, 11 Mar 2026 16:00:53 -0400
Subject: [PATCH 07/16] clarify state field

---
 src/middlewared/middlewared/api/v27_0_0/interface.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index e0aa5fa49cb5b..5773cc9f6993f 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -133,7 +133,10 @@ class InterfaceEntry(BaseModel):
     type: str
     """Type of interface (PHYSICAL, BRIDGE, LINK_AGGREGATION, VLAN, etc.)."""
     state: InterfaceEntryState
-    """Current runtime state information for the interface."""
+    """Current runtime state of the interface as reported by the OS kernel. This reflects what is actually configured \
+    in the kernel at query time and may differ from the top-level fields, which represent the persisted database \
+    configuration. Pending changes (after `interface.update` but before `interface.commit`) will not be visible here \
+    until the commit is applied and the interface is synchronized."""
     aliases: list[InterfaceEntryAlias]
     """List of IP address aliases configured on the interface."""
     ipv4_dhcp: bool

From 9d9fd76b67918e3e8bb41ff698d92b8cdd47100a Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Fri, 13 Mar 2026 13:41:35 -0400
Subject: [PATCH 08/16] merge migration

---
 .../27.0/2026-03-09_19-16_ScrubNotStarted.py  |  4 ++--
 .../versions/27.0/2026-03-13_17-05_.py        | 24 +++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py

diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
index eddd9c5310d93..af5f48ea5fed8 100644
--- a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-09_19-16_ScrubNotStarted.py
@@ -1,7 +1,7 @@
 """Remove ScrubNotStarted alerts
 
 Revision ID: 3fc58b28ce77
-Revises: ad6bd79a37d7
+Revises: f3b4b0f4b0cf
 Create Date: 2026-03-09 19:16:31.067201+00:00
 
 """
@@ -11,7 +11,7 @@
 
 # revision identifiers, used by Alembic.
 revision = '3fc58b28ce77'
-down_revision = 'ad6bd79a37d7'
+down_revision = 'f3b4b0f4b0cf'
 branch_labels = None
 depends_on = None
 
diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py
new file mode 100644
index 0000000000000..03dd0a275cb26
--- /dev/null
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py
@@ -0,0 +1,24 @@
+"""empty message
+
+Revision ID: ef6c293fc34f
+Revises: 3fc58b28ce77
+Create Date: 2026-03-13 17:05:46.399951+00:00
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'ef6c293fc34f'
+down_revision = ('ad6bd79a37d7', '3fc58b28ce77')
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    pass
+
+
+def downgrade():
+    pass

From 2e0373f39a67ca2056aea221ccb5865ef8abd714 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Fri, 13 Mar 2026 14:03:14 -0400
Subject: [PATCH 09/16] make available_fec_modes synchronous

---
 src/middlewared/middlewared/plugins/network.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 36d7fb076033d..6379b228c8647 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -1230,7 +1230,7 @@ async def do_update(self, audit_callback, oid, data):
             verrors.add('interface_update.dhcp', 'Enabling DHCPv4/v6 on HA systems is unsupported.')
         if 'fec_mode' in data:
             if new['type'] == 'PHYSICAL':
-                if available := await self.available_fec_modes(oid):
+                if available := self.available_fec_modes(oid):
                     if data['fec_mode'] not in available:
                         verrors.add(
                             'interface_update.fec_mode',
@@ -1485,13 +1485,13 @@ async def lacpdu_rate_choices(self):
         return {i.value: i.value for i in LacpduRateChoices}
 
     @api_method(InterfaceAvailableFecModesArgs, InterfaceAvailableFecModesResult, roles=['NETWORK_INTERFACE_READ'])
-    async def available_fec_modes(self, id_):
+    def available_fec_modes(self, id_):
         """
         Returns FEC modes supported by interface `id`.
 
         Returns an empty list if the interface does not exist or does not support FEC.
         """
-        return await self.middleware.run_in_thread(get_ethtool().get_fec_modes, id_)
+        return get_ethtool().get_fec_modes(id_)
 
     @api_method(InterfaceChoicesArgs, InterfaceChoicesResult, roles=['NETWORK_INTERFACE_READ'])
     async def choices(self, options):

From 108b78391b9f0cdfe1f38d0b73225f44b6c900b6 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Fri, 13 Mar 2026 14:14:05 -0400
Subject: [PATCH 10/16] rename migration

---
 .../27.0/{2026-03-13_17-05_.py => 2026-03-13_17-05_merge.py}    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
 rename src/middlewared/middlewared/alembic/versions/27.0/{2026-03-13_17-05_.py => 2026-03-13_17-05_merge.py} (95%)

diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py
similarity index 95%
rename from src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py
rename to src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py
index 03dd0a275cb26..fe566cc03a55a 100644
--- a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_.py
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py
@@ -1,4 +1,4 @@
-"""empty message
+"""Merge.
 
 Revision ID: ef6c293fc34f
 Revises: 3fc58b28ce77

From bccdbfe8d795d3b4c40e6d1ddb408ecc0b40c1ad Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Tue, 17 Mar 2026 10:28:16 -0400
Subject: [PATCH 11/16] only allow changing fec_mode on enterprise systems

---
 .../middlewared/plugins/network.py            | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 6379b228c8647..9aa5a4fbd0e0b 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -1228,18 +1228,25 @@ async def do_update(self, audit_callback, oid, data):
         )
         if await self.middleware.call('failover.licensed') and (new.get('ipv4_dhcp') or new.get('ipv6_auto')):
             verrors.add('interface_update.dhcp', 'Enabling DHCPv4/v6 on HA systems is unsupported.')
+
+        # Validate fec_mode field
         if 'fec_mode' in data:
-            if new['type'] == 'PHYSICAL':
-                if available := self.available_fec_modes(oid):
-                    if data['fec_mode'] not in available:
+            if await self.middleware.call('system.is_enterprise'):
+                if new['type'] == 'PHYSICAL':
+                    if available := self.available_fec_modes(oid):
+                        if data['fec_mode'] not in available:
+                            verrors.add(
+                                'interface_update.fec_mode',
+                                f'Unsupported FEC mode. Available: {", ".join(available)}'
+                            )
+                    else:
                         verrors.add(
-                            'interface_update.fec_mode',
-                            f'Unsupported FEC mode. Available: {", ".join(available)}'
+                            'interface_update.fec_mode', 'This interface does not support FEC mode configuration.'
                         )
                 else:
-                    verrors.add('interface_update.fec_mode', 'This interface does not support FEC mode configuration.')
+                    verrors.add('interface_update.fec_mode', 'FEC mode can only be set on physical interfaces.')
             else:
-                verrors.add('interface_update.fec_mode', 'FEC mode can only be set on physical interfaces.')
+                verrors.add('interface_update.fec_mode', 'Configuring FEC mode is an enterprise feature.')
 
         verrors.check()
 

From 4c9604dffd4c9b4e255d694dd38fef7ee00af190 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Tue, 17 Mar 2026 10:37:59 -0400
Subject: [PATCH 12/16] update merge migration

---
 .../{2026-03-13_17-05_merge.py => 2026-03-17_14-37_merge.py}  | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
 rename src/middlewared/middlewared/alembic/versions/27.0/{2026-03-13_17-05_merge.py => 2026-03-17_14-37_merge.py} (80%)

diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
similarity index 80%
rename from src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py
rename to src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
index fe566cc03a55a..6a99294bf9604 100644
--- a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-13_17-05_merge.py
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
@@ -1,7 +1,7 @@
 """Merge.
 
 Revision ID: ef6c293fc34f
-Revises: 3fc58b28ce77
+Revises: aa197df8684c
 Create Date: 2026-03-13 17:05:46.399951+00:00
 
 """
@@ -11,7 +11,7 @@
 
 # revision identifiers, used by Alembic.
 revision = 'ef6c293fc34f'
-down_revision = ('ad6bd79a37d7', '3fc58b28ce77')
+down_revision = ('ad6bd79a37d7', 'aa197df8684c')
 branch_labels = None
 depends_on = None
 

From 11ca975eb97aa31fe846fea8312712403a638c31 Mon Sep 17 00:00:00 2001
From: Logan Cary <carylog9@gmail.com>
Date: Tue, 17 Mar 2026 18:19:42 -0400
Subject: [PATCH 13/16] API doc

---
 src/middlewared/middlewared/api/v26_0_0/interface.py | 4 ++++
 src/middlewared/middlewared/api/v27_0_0/interface.py | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index 941251a494357..0584ee90505aa 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -301,6 +301,10 @@ class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     """
     Forward Error Correction (FEC) mode. Only valid for physical interfaces.
 
+    Configuring this field is only available on enterprise systems. It should be used as directed by TrueNAS Support \
+    for resolving link negotiation failures due to FEC mismatches with the upstream switch. Improper configuration of \
+    this field can cause a healthy interface to go down.
+
     * "AUTO": Selects the best FEC mode based on cable/port capabilities
     * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
     * "BASER": BaseR-FEC (FireCode)
diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index 5773cc9f6993f..00467f7e1db34 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -303,6 +303,11 @@ class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]
     """
     Forward Error Correction (FEC) mode. Only valid for physical interfaces.
+
+    Configuring this field is only available on enterprise systems. It should be used as directed by TrueNAS Support \
+    for resolving link negotiation failures due to FEC mismatches with the upstream switch. Improper configuration of \
+    this field can cause a healthy interface to go down.
+
     * "AUTO": Selects the best FEC mode based on cable/port capabilities
     * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
     * "BASER": BaseR-FEC (FireCode)

From 96c3c11c43f88125042e1cf08ad298ea010466aa Mon Sep 17 00:00:00 2001
From: Logan Cary <carylog9@gmail.com>
Date: Tue, 17 Mar 2026 18:25:10 -0400
Subject: [PATCH 14/16] appease import linter

---
 src/middlewared/middlewared/api/v26_0_0/interface.py | 4 +++-
 src/middlewared/middlewared/api/v27_0_0/interface.py | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index 0584ee90505aa..325cc8be5e9ed 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -2,7 +2,6 @@
 
 from pydantic import Field
 
-from truenas_pynetif.ethtool import FecModeName
 from middlewared.api.base import (
     BaseModel, IPv4Address, UniqueList, IPvAnyAddress, Excluded, excluded_field, ForUpdateMetaclass,
     single_argument_args, single_argument_result, NotRequired, NonEmptyString,
@@ -28,6 +27,9 @@
 ]
 
 
+FecModeName = Literal["AUTO", "OFF", "RS", "BASER", "LLRS"]
+
+
 class InterfaceEntryAlias(BaseModel):
     type: str
     """The type of IP address (INET for IPv4, INET6 for IPv6)."""
diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index 00467f7e1db34..9b93f723124db 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -2,7 +2,6 @@
 
 from pydantic import Field
 
-from truenas_pynetif.ethtool import FecModeName
 from middlewared.api.base import (
     BaseModel, IPv4Address, UniqueList, IPvAnyAddress, Excluded, excluded_field, ForUpdateMetaclass,
     single_argument_args, single_argument_result, NotRequired, NonEmptyString,
@@ -28,6 +27,9 @@
 ]
 
 
+FecModeName = Literal["AUTO", "OFF", "RS", "BASER", "LLRS"]
+
+
 class InterfaceEntryAlias(BaseModel):
     type: str
     """The type of IP address (INET for IPv4, INET6 for IPv6)."""

From 07cb0b0d8d580fc437ebdc35d743730b1f1e5ee4 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Wed, 18 Mar 2026 14:06:53 -0400
Subject: [PATCH 15/16] use FecModeName alias consistently

---
 src/middlewared/middlewared/api/v26_0_0/interface.py | 6 +++---
 src/middlewared/middlewared/api/v27_0_0/interface.py | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index 325cc8be5e9ed..acf0749fbebfa 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -121,7 +121,7 @@ class InterfaceEntryState(BaseModel):
     pcp: int | None = NotRequired
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] | None = NotRequired
+    fec_mode: FecModeName | None = NotRequired
     """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
 
 
@@ -146,7 +146,7 @@ class InterfaceEntry(BaseModel):
     """Human-readable description of the interface."""
     mtu: int | None
     """Maximum transmission unit size for the interface."""
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] = NotRequired
+    fec_mode: FecModeName = NotRequired
     """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
@@ -299,7 +299,7 @@ class InterfaceServicesRestartedOnSyncItem(BaseModel):
 
 class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     type: Excluded = excluded_field()
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]
+    fec_mode: FecModeName
     """
     Forward Error Correction (FEC) mode. Only valid for physical interfaces.
 
diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index 9b93f723124db..cfe170da62193 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -121,7 +121,7 @@ class InterfaceEntryState(BaseModel):
     pcp: int | None = NotRequired
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] | None = NotRequired
+    fec_mode: FecModeName | None = NotRequired
     """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
 
 
@@ -149,7 +149,7 @@ class InterfaceEntry(BaseModel):
     """Human-readable description of the interface."""
     mtu: int | None
     """Maximum transmission unit size for the interface."""
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"] = NotRequired
+    fec_mode: FecModeName = NotRequired
     """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
@@ -302,7 +302,7 @@ class InterfaceServicesRestartedOnSyncItem(BaseModel):
 
 class InterfaceUpdate(InterfaceCreate, metaclass=ForUpdateMetaclass):
     type: Excluded = excluded_field()
-    fec_mode: Literal["AUTO", "RS", "BASER", "OFF", "LLRS"]
+    fec_mode: FecModeName
     """
     Forward Error Correction (FEC) mode. Only valid for physical interfaces.
 

From a1c12dc9fdd41d4e35d145a8063ec9b12a71b072 Mon Sep 17 00:00:00 2001
From: Logan Cary <logan.cary@ixsystems.com>
Date: Wed, 18 Mar 2026 14:32:49 -0400
Subject: [PATCH 16/16] address reviews

---
 .../versions/27.0/2026-03-17_14-37_merge.py   |  6 ++--
 .../middlewared/api/v26_0_0/interface.py      | 28 +++++++++++++++++--
 .../middlewared/api/v27_0_0/interface.py      | 28 +++++++++++++++++--
 .../middlewared/plugins/network.py            |  8 ++++--
 4 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
index 6a99294bf9604..dc4a154e650b6 100644
--- a/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
+++ b/src/middlewared/middlewared/alembic/versions/27.0/2026-03-17_14-37_merge.py
@@ -1,7 +1,7 @@
-"""Merge.
+"""Merge migration for NAS-139477 adding FEC mode (revision ad6bd79a37d7).
 
 Revision ID: ef6c293fc34f
-Revises: aa197df8684c
+Revises: aa197df8684c, ad6bd79a37d7
 Create Date: 2026-03-13 17:05:46.399951+00:00
 
 """
@@ -11,7 +11,7 @@
 
 # revision identifiers, used by Alembic.
 revision = 'ef6c293fc34f'
-down_revision = ('ad6bd79a37d7', 'aa197df8684c')
+down_revision = ('aa197df8684c', 'ad6bd79a37d7')
 branch_labels = None
 depends_on = None
 
diff --git a/src/middlewared/middlewared/api/v26_0_0/interface.py b/src/middlewared/middlewared/api/v26_0_0/interface.py
index acf0749fbebfa..8a636ab6d051f 100644
--- a/src/middlewared/middlewared/api/v26_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v26_0_0/interface.py
@@ -122,7 +122,15 @@ class InterfaceEntryState(BaseModel):
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
     fec_mode: FecModeName | None = NotRequired
-    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
+    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    * `null`: FEC not supported or mode cannot be determined
+    """
 
 
 class InterfaceEntry(BaseModel):
@@ -147,7 +155,14 @@ class InterfaceEntry(BaseModel):
     mtu: int | None
     """Maximum transmission unit size for the interface."""
     fec_mode: FecModeName = NotRequired
-    """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
+    """Forward Error Correction (FEC) mode. Only valid for physical interfaces.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
     vlan_tag: int | None = NotRequired
@@ -552,4 +567,11 @@ class InterfaceAvailableFecModesArgs(BaseModel):
 
 class InterfaceAvailableFecModesResult(BaseModel):
     result: list[FecModeName]
-    """List of FEC modes supported by the interface. Empty list if FEC is not supported."""
+    """List of FEC modes supported by the interface. Empty list if FEC is not supported.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
diff --git a/src/middlewared/middlewared/api/v27_0_0/interface.py b/src/middlewared/middlewared/api/v27_0_0/interface.py
index cfe170da62193..d9c3e5f59aef6 100644
--- a/src/middlewared/middlewared/api/v27_0_0/interface.py
+++ b/src/middlewared/middlewared/api/v27_0_0/interface.py
@@ -122,7 +122,15 @@ class InterfaceEntryState(BaseModel):
     """Priority Code Point for VLAN traffic prioritization. Values 0-7 map to different QoS priority levels, \
     with 0 being lowest and 7 highest priority."""
     fec_mode: FecModeName | None = NotRequired
-    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces."""
+    """Currently active Forward Error Correction mode from the hardware. Only present for physical interfaces.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    * `null`: FEC not supported or mode cannot be determined
+    """
 
 
 class InterfaceEntry(BaseModel):
@@ -150,7 +158,14 @@ class InterfaceEntry(BaseModel):
     mtu: int | None
     """Maximum transmission unit size for the interface."""
     fec_mode: FecModeName = NotRequired
-    """Forward Error Correction (FEC) mode. Only valid for physical interfaces."""
+    """Forward Error Correction (FEC) mode. Only valid for physical interfaces.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
     vlan_parent_interface: str | None = NotRequired
     """Parent interface for VLAN configuration."""
     vlan_tag: int | None = NotRequired
@@ -555,4 +570,11 @@ class InterfaceAvailableFecModesArgs(BaseModel):
 
 class InterfaceAvailableFecModesResult(BaseModel):
     result: list[FecModeName]
-    """List of FEC modes supported by the interface. Empty list if FEC is not supported."""
+    """List of FEC modes supported by the interface. Empty list if FEC is not supported.
+
+    * "AUTO": Selects the best FEC mode based on cable/port capabilities
+    * "RS": RS-FEC (Reed-Solomon), often used for 25GbE/100GbE+ NICs
+    * "BASER": BaseR-FEC (FireCode)
+    * "OFF": Disables FEC
+    * "LLRS": Low Latency Reed-Solomon FEC, used for 25GBASE-KR/CR
+    """
diff --git a/src/middlewared/middlewared/plugins/network.py b/src/middlewared/middlewared/plugins/network.py
index 9aa5a4fbd0e0b..6dfdaad82d0c1 100644
--- a/src/middlewared/middlewared/plugins/network.py
+++ b/src/middlewared/middlewared/plugins/network.py
@@ -33,7 +33,7 @@
 from middlewared.utils.filter_list import filter_list
 from truenas_pynetif.address.constants import AddressFamily
 from truenas_pynetif.address.netlink import get_addresses, get_default_route, netlink_route
-from truenas_pynetif.ethtool import get_ethtool
+from truenas_pynetif.ethtool import NetlinkError, get_ethtool
 from truenas_pynetif.interface import CLONED_PREFIXES
 from truenas_pynetif.interface_state import list_interface_states
 from truenas_pynetif.utils import INTERNAL_INTERFACES
@@ -1498,7 +1498,11 @@ def available_fec_modes(self, id_):
 
         Returns an empty list if the interface does not exist or does not support FEC.
         """
-        return get_ethtool().get_fec_modes(id_)
+        try:
+            return get_ethtool().get_fec_modes(id_)
+        except NetlinkError as e:
+            self.logger.error(f'Failed to retrieve available FEC modes for {id_}', exc_info=e)
+            return []
 
     @api_method(InterfaceChoicesArgs, InterfaceChoicesResult, roles=['NETWORK_INTERFACE_READ'])
     async def choices(self, options):