[Bug 2141900] [NEW] igc: I225-V intermittent ENETUNREACH regression in 6.8.0-100 (ring buffer 256)

Public bug reported:

After upgrading from 6.8.0-94-generic (igc srcversion
52B58AAD759A5082561BC0D) to 6.8.0-100-generic (igc srcversion
347E58340A3FF0762D4EF73), the Intel I225-V (rev 03) intermittently
returns ENETUNREACH on outbound WAN connections despite valid routing
table, ARP, and link state.

Hardware: ASUS ROG Strix X570-I Gaming, Intel I225-V rev 03, firmware
1057:8754, PCIe 06:00.0

Symptoms:
- ~37% of TCP connect() and ICMP to WAN destinations fail with ENETUNREACH
- LAN connectivity to gateway is 100% reliable
- Link stays UP, carrier present, zero error counters in ethtool -S
- Routing table and ARP cache are correct during failures
- No firewall rules on INPUT/OUTPUT chains
- Issue is isolated to this machine; other devices on same LAN unaffected

Root cause: Default TX/RX ring buffer size of 256. Increasing to 1024
(ethtool -G enp6s0 rx 1024 tx 1024) eliminates the issue completely.
Same ring buffer size of 256 was stable on 6.8.0-94.

Workaround: ethtool -G enp6s0 rx 1024 tx 1024

Reproducer:
# With default ring buffers (256):
for i in $(seq 1 30); do
timeout 2 bash -c 'echo > /dev/tcp/8.8.8.8/443' 2>&1 && echo OK || echo FAIL
sleep 2
done
# Expect ~37% FAIL with "Network is unreachable"

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-6.8.0-100-generic 6.8.0-100.100
ProcVersionSignature: Ubuntu 6.8.0-100.100-generic 6.8.12
Uname: Linux 6.8.0-100-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.8
Architecture: amd64
CRDA: N/A
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Mon Feb 16 05:29:52 2026
InstallationDate: Installed on 2023-11-05 (833 days ago)
InstallationMedia: Kubuntu 22.04.3 LTS "Jammy Jellyfish" - Release amd64 (20230807.1)
MachineType: ASUS System Product Name
ProcFB: 0 amdgpudrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-100-generic root=/dev/mapper/vgkubuntu-root ro quiet splash vt.handoff=7
RelatedPackageVersions:
linux-restricted-modules-6.8.0-100-generic N/A
linux-backports-modules-6.8.0-100-generic N/A
linux-firmware 20240318.git3b128b60-0ubuntu2.23
RfKill:

SourcePackage: linux
UpgradeStatus: Upgraded to noble on 2024-09-03 (530 days ago)
dmi.bios.date: 10/27/2022
dmi.bios.release: 5.17
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2806
dmi.board.asset.tag: Default string
dmi.board.name: ROG STRIX B550-F GAMING
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev X.0x
dmi.chassis.asset.tag: Default string
dmi.chassis.type: 3
dmi.chassis.vendor: Default string
dmi.chassis.version: Default string
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2806:bd10/27/2022:br5.17:svnASUS:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnROGSTRIXB550-FGAMING:rvrRevX.0x:cvnDefaultstring:ct3:cvrDefaultstring:skuSKU:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: System Product Name
dmi.product.sku: SKU
dmi.product.version: System Version
dmi.sys.vendor: ASUS

** Affects: linux (Ubuntu)
Importance: Undecided
Status: New


** Tags: amd64 apport-bug noble

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https://bugs.launchpad.net/bugs/2141900

Title:
igc: I225-V intermittent ENETUNREACH regression in 6.8.0-100 (ring
buffer 256)

Status in linux package in Ubuntu:
New

Bug description:
After upgrading from 6.8.0-94-generic (igc srcversion
52B58AAD759A5082561BC0D) to 6.8.0-100-generic (igc srcversion
347E58340A3FF0762D4EF73), the Intel I225-V (rev 03) intermittently
returns ENETUNREACH on outbound WAN connections despite valid routing
table, ARP, and link state.

Hardware: ASUS ROG Strix X570-I Gaming, Intel I225-V rev 03,
firmware 1057:8754, PCIe 06:00.0

Symptoms:
- ~37% of TCP connect() and ICMP to WAN destinations fail with ENETUNREACH
- LAN connectivity to gateway is 100% reliable
- Link stays UP, carrier present, zero error counters in ethtool -S
- Routing table and ARP cache are correct during failures
- No firewall rules on INPUT/OUTPUT chains
- Issue is isolated to this machine; other devices on same LAN unaffected

Root cause: Default TX/RX ring buffer size of 256. Increasing to
1024 (ethtool -G enp6s0 rx 1024 tx 1024) eliminates the issue
completely. Same ring buffer size of 256 was stable on 6.8.0-94.

Workaround: ethtool -G enp6s0 rx 1024 tx 1024

Reproducer:
# With default ring buffers (256):
for i in $(seq 1 30); do
timeout 2 bash -c 'echo > /dev/tcp/8.8.8.8/443' 2>&1 && echo OK || echo FAIL
sleep 2
done
# Expect ~37% FAIL with "Network is unreachable"

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-6.8.0-100-generic 6.8.0-100.100
ProcVersionSignature: Ubuntu 6.8.0-100.100-generic 6.8.12
Uname: Linux 6.8.0-100-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.8
Architecture: amd64
CRDA: N/A
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Mon Feb 16 05:29:52 2026
InstallationDate: Installed on 2023-11-05 (833 days ago)
InstallationMedia: Kubuntu 22.04.3 LTS "Jammy Jellyfish" - Release amd64 (20230807.1)
MachineType: ASUS System Product Name
ProcFB: 0 amdgpudrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-100-generic root=/dev/mapper/vgkubuntu-root ro quiet splash vt.handoff=7
RelatedPackageVersions:
linux-restricted-modules-6.8.0-100-generic N/A
linux-backports-modules-6.8.0-100-generic N/A
linux-firmware 20240318.git3b128b60-0ubuntu2.23
RfKill:

SourcePackage: linux
UpgradeStatus: Upgraded to noble on 2024-09-03 (530 days ago)
dmi.bios.date: 10/27/2022
dmi.bios.release: 5.17
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2806
dmi.board.asset.tag: Default string
dmi.board.name: ROG STRIX B550-F GAMING
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev X.0x
dmi.chassis.asset.tag: Default string
dmi.chassis.type: 3
dmi.chassis.vendor: Default string
dmi.chassis.version: Default string
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2806:bd10/27/2022:br5.17:svnASUS:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnROGSTRIXB550-FGAMING:rvrRevX.0x:cvnDefaultstring:ct3:cvrDefaultstring:skuSKU:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: System Product Name
dmi.product.sku: SKU
dmi.product.version: System Version
dmi.sys.vendor: ASUS

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