Re: CVS commit: src/sys/net

[Tobias Nygren <tnn%NetBSD.org@localhost>]

On Mon, 15 Nov 2021 07:07:06 +0000
Shoichi YAMAGUCHI <yamaguchi%netbsd.org@localhost> wrote:

> Date:		Mon Nov 15 07:07:06 UTC 2021
> 
> Modified Files:
> 	src/sys/net: if_ether.h if_ethersubr.c if_vlan.c
> 	src/sys/net/lagg: if_lagg.c
> 
> Log Message:
> introduced APIs to configure VLAN TAG to ethernet devices

Hello,

This change seems to have broke something MTU related when
more than two VLANs are configured on the same NIC.
The first VLAN inherits the parent's MTU but the subsequent
ones have 4 byte too small MTU causing network problems.

Kernel from 2021-11-15:

# ifconfig |grep mtu
wm0: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan100: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan101: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan102: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan103: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan104: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan105: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan106: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500

Kernel from 2021-11-16:

wm0: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan100: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
vlan101: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496
vlan102: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496
vlan103: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496
vlan104: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496
vlan105: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496
vlan106: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1496

I could not force increase the MTU either:

root@tinfoilhat-b:log> ifconfig vlan100 mtu 1500
root@tinfoilhat-b:log> ifconfig vlan101 mtu 1500
ifconfig: SIOCSIFMTU: Invalid argument

Kind regards,
-Tobias