Created attachment 205181 [details] One line patch to set IFCAP_VLAN_MTU capability. Do not drop the MTU from from 1500 to 1496 bytes when setting up a VLAN. The chip is already configured for a maximum length of 1518 bytes. See if_muge.c lines 1135ff at base r348020. According to my tests adding IFCAP_VLAN_MTU to ifp->if_capabilities fixes this. See also base r291953 for the same fix at the smsc(4) driver.
A commit references this bug: Author: emaste Date: Tue Jul 2 16:44:05 UTC 2019 New revision: 349602 URL: https://svnweb.freebsd.org/changeset/base/349602 Log: if_muge: set IFCAP_VLAN_MTU to maintain 1500 MTU with vlan use PR: 238665 Submitted by: Ralf <iz-rpi03@hs-karlsruhe.de> MFC after: 1 week Changes: head/sys/dev/usb/net/if_muge.c
A commit references this bug: Author: emaste Date: Sun Mar 8 18:22:37 UTC 2020 New revision: 358762 URL: https://svnweb.freebsd.org/changeset/base/358762 Log: MFC r349602: if_muge: set IFCAP_VLAN_MTU to maintain 1500 MTU with vlan use PR: 238665 Submitted by: Ralf <iz-rpi03@hs-karlsruhe.de> Changes: _U stable/12/ stable/12/sys/dev/usb/net/if_muge.c