PPPoE over vlan RFC4638 MTU issue

[staticznld]

Hi,

I am running opnsense 19.1.1 on a Qotom Q555g6 Intel Core I5-7200u 8GB RAM 120 GB SSD.
My  ISP is KPN Fiber "Netherlands". It does support RFC4638 tested with the Experiabox supplied by ISP.

Setup

NTU - Opnsense - Vlan6 - PPPoE over vlan6.

When MTU on interface WAN is set to 1500 the actual MTU is 1492 as expected as the PPPoE tunnes uses 8 bytes.

Code: [Select]

igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=6503bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
        ether 40:62:31:02:cb:17
        hwaddr 40:62:31:02:cb:17
        inet6 fe80::4262:31ff:fe02:cb17%igb0 prefixlen 64 scopeid 0x1
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active

igb0_vlan6: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=600303<RXCSUM,TXCSUM,TSO4,TSO6,RXCSUM_IPV6,TXCSUM_IPV6>
        ether 40:62:31:02:cb:17
        inet6 fe80::4262:31ff:fe02:cb17%igb0_vlan6 prefixlen 64 scopeid 0xc
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
        vlan: 6 vlanpcp: 0 parent interface: igb0
        groups: vlan


pppoe0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metric 0 mtu 1492
        inet6 fe80::4262:31ff:fe02:cb17%pppoe0 prefixlen 64 scopeid 0xd
        inet6 fe80::4262:31ff:fe02:cb18%pppoe0 prefixlen 64 scopeid 0xd
        inet xxx.xxx.xxx.xxx --> xxx.xxx.xxx.xxx netmask 0xffffffff
        nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>


When setting the MTU on the WAN interface to 1508 I get an mtu of 1500 as expected!
But the internet connection is far from stable only Google looks reachable.
When looking in the console to the ifconfig output I expected an MTU from 1508 on the Vlan interface and the parent interface igb0 but they are still 1500.

Code: [Select]

igb0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=6503bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6>
        ether 40:62:31:02:cb:17
        hwaddr 40:62:31:02:cb:17
        inet6 fe80::4262:31ff:fe02:cb17%igb0 prefixlen 64 scopeid 0x1
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        media: Ethernet autoselect (1000baseT <full-duplex>)

igb0_vlan6: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=600303<RXCSUM,TXCSUM,TSO4,TSO6,RXCSUM_IPV6,TXCSUM_IPV6>
        ether 40:62:31:02:cb:17
        inet6 fe80::4262:31ff:fe02:cb17%igb0_vlan6 prefixlen 64 scopeid 0xc
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
        vlan: 6 vlanpcp: 0 parent interface: igb0
        groups: vlan

pppoe0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metric 0 mtu 1500
        inet6 fe80::4262:31ff:fe02:cb17%pppoe0 prefixlen 64 scopeid 0xd
        inet6 fe80::4262:31ff:fe02:cb18%pppoe0 prefixlen 64 scopeid 0xd
        inet xxx.xxx.xxx.xxx --> xxx.xxx.xxx.xxx netmask 0xffffffff
        nd6 options=23<PERFORMNUD,ACCEPT_RTADV,AUTO_LINKLOCAL>


[staticznld]

Anyone any idea how to correct the problem?

[staticznld]

Update,

When setting MTU to 1508 with the shell via "ifconfig igb0 mtu 1508 up" and "ifconfig igb0_vlan6 mtu 1508 up"
Everything is working as expected!

After reboot MTU 1508 is gone, how is it possible to make this setting permanent?

Update 2,

When adding IGB0 as interface and set MTU to 1508 everything is worked as expected.
Through ifconfig vlan is still 1500 but everything is working.

[AdSchellevis]

We probably need the exact configured settings (without user/pass/addresses), there might be something off, although it could also be a configuration issue not validated correctly.

The relevant configuration parts are the interface (all configured on igb0) and the devices in "interfaces" --> "point to point"