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Tasklist

FS#37082 - constantly changing MTU from 1500 to 1492 and vice versa makes ethernet controller unusable

Attached to Project: Arch Linux
Opened by John Barranco (Mr_Kartoffelsalat.) - Friday, 27 September 2013, 04:03 GMT
Last edited by Gerardo Exequiel Pozzi (djgera) - Friday, 27 September 2013, 22:03 GMT
Task Type Bug Report
Category Packages: Extra
Status Closed
Assigned To No-one
Architecture All
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Description:
Plugging in the LAN-cable makes
e1000e constantly changing the MTU from 1500 to 1492 . No network connection can be made.


Additional info:
Can be worked around by setting the MTU manually to 1492:

# ifconfig eth0 mtu 1492

* package version(s)
3.11.1-2-ARCH x86_64
netctl 1.3-1
ifplugd 0.28-14

* config and/or log files etc.
dmesg:
[ 150.428579] e1000e 0000:00:19.0: irq 47 for MSI/MSI-X
[ 150.530418] e1000e 0000:00:19.0: irq 47 for MSI/MSI-X
[ 150.530923] IPv6: ADDRCONF(NETDEV_UP): enp0s25: link is not ready
[ 482.997667] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 482.997788] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
[ 482.997844] IPv6: ADDRCONF(NETDEV_CHANGE): enp0s25: link becomes ready
[ 490.525844] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 490.778571] e1000e 0000:00:19.0 enp0s25: changing MTU from 1492 to 1500
[ 492.641036] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 492.641157] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
[ 497.145788] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 497.357750] e1000e 0000:00:19.0 enp0s25: changing MTU from 1492 to 1500
[ 499.087834] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 499.087956] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
[ 504.757714] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 505.003024] e1000e 0000:00:19.0 enp0s25: changing MTU from 1492 to 1500
[ 506.871018] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 506.871139] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
[ 511.772807] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 511.980980] e1000e 0000:00:19.0 enp0s25: changing MTU from 1492 to 1500
[ 513.711152] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 513.711274] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
[ 518.488545] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 518.740589] e1000e 0000:00:19.0 enp0s25: changing MTU from 1492 to 1500
[ 519.585098] e1000e 0000:00:19.0 enp0s25: changing MTU from 1500 to 1492
[ 521.334345] e1000e: enp0s25 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[ 521.334467] e1000e 0000:00:19.0 enp0s25: 10/100 speed: disabling TSO
going on until LANcable is unplugged

Ethernet controller: Intel Corporation 82567LM Gigabit Network Connection




Steps to reproduce:
In my case: reboot, plug LAN cable in.
This task depends upon

Closed by  Gerardo Exequiel Pozzi (djgera)
Friday, 27 September 2013, 22:03 GMT
Reason for closing:  Not a bug
Comment by Jan de Groot (JGC) - Friday, 27 September 2013, 09:55 GMT
This is an issue with e1000 and dhcpcd. Your DHCP server wants to enfore an MTU of 1492. dhcpcd acquires a lease, finds out that MTU has to be changed to 1492, driver resets the link when setting MTU, dhcpcd notices this, restores MTU to 1500 and the same story repeats itself until either you force it to 1492 or you kill dhcpcd.

No idea why you want to cripple your LAN interface by lowering the MTU (standard is 1500), so you might want to remove the option to request MTU from dhcpcd.conf
Comment by John Barranco (Mr_Kartoffelsalat.) - Friday, 27 September 2013, 22:02 GMT
Thank you very much, removing the option to request MTU from dhcpcd.conf did the trick.

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