<div dir="ltr"><div>tun interfaces cannot be put in a bridge because they do not use an Ethernet-like L2 link-layer header (or any L2 header at all, really; they're purely L3 interfaces).</div><div> </div><div>You need to use a 'tap' interface instead. </div></div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jan 31, 2023 at 1:05 PM Thomas Köller <<a href="mailto:thomas@koeller.dyndns.org">thomas@koeller.dyndns.org</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I am trying to build a VPN tunnel through a tun interface created by sshd. The tun interface is to be added to an existing bridge interface. For this purpose I created a .network file (see below). However, the operation fails, without systemd-networkd giving a useful error message beyond 'Invalid argument', not even if logging is set do debug: Jan 31 11:04:59 sarkovy systemd-networkd[1294]: Setting log level to debug. Jan 31 11:04:59 sarkovy systemd-networkd[1294]: Sent message type=method_return sender=n/a destination=:1.213 path=n/a interface=n/a member=n/a cookie=44 reply_cookie=3 signature=n/a error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Saved new link: ifindex=6, iftype=NONE(65534), kind=tun Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Saved original MTU 1500 (min: 68, max: 65535) Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Saved IPv6 link-local address generation mode: eui64 Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Flags change: +MULTICAST +POINTOPOINT +NOARP Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=45 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: link pending udev initialization... Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: udev initialized link Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: State changed: pending -> initialized Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=46 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Found driver: tun Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Link state is up-to-date Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Unmanaging interface. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: State changed: initialized -> unmanaged Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=47 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: tun0: Interface name change detected, renamed to vpn_rpi400. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: udev initialized link Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: State changed: unmanaged -> initialized Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=48 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Link state is up-to-date Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: found matching network '/etc/systemd/network/50-vpn.network'. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Configuring with /etc/systemd/network/50-vpn.network. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: State changed: initialized -> configuring Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=49 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link is not activated. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link is not activated. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Setting '/proc/sys/net/ipv6/conf/vpn_rpi400/use_tempaddr' to '0' Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Setting '/proc/sys/net/ipv6/conf/vpn_rpi400/accept_ra' to '0' Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Setting '/proc/sys/net/ipv6/conf/vpn_rpi400/proxy_ndp' to '0' Jan 31 11:05:12 sarkovy systemd-networkd[1294]: No change in value '0', suppressing write Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Setting '/proc/sys/net/ipv4/conf/vpn_rpi400/promote_secondaries' to '1' Jan 31 11:05:12 sarkovy systemd-networkd[1294]: No change in value '1', suppressing write Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Requested to set link flags Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Requested to set IPv6LL address generation mode Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Requested to set master interface Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Requested to set bridge configurations Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Requested to activate link Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link_check_ready(): link layer is configuring. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Setting link flags Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Setting IPv6LL address generation mode Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Setting master interface Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: link flags set. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: IPv6LL address generation mode set. Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Failed to set master interface: Invalid argument Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: Failed Jan 31 11:05:12 sarkovy systemd-networkd[1294]: vpn_rpi400: State changed: configuring -> failed Jan 31 11:05:12 sarkovy systemd-networkd[1294]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_36 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=50 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a Jan 31 11:05:26 sarkovy systemd-networkd[1294]: Got message type=method_call sender=:1.215 destination=org.freedesktop.network1 path=/org/freedesktop/network1 interface=org.freedesktop.DBus.Properties member=Get cookie=2 reply_cookie=0 signature=ss error-name=n/a error-message=n/a Jan 31 11:05:26 sarkovy systemd-networkd[1294]: Sent message type=method_return sender=n/a destination=:1.215 path=n/a interface=n/a member=n/a cookie=51 reply_cookie=2 signature=v error-name=n/a error-message=n/a Jan 31 11:06:35 sarkovy systemd-networkd[1294]: Got message type=method_call sender=:1.216 destination=org.freedesktop.network1 path=/org/freedesktop/LogControl1 interface=org.freedesktop.DBus.Properties member=Set cookie=3 reply_cookie=0 signature=ssv error-name=n/a error-message=n/a Jan 31 11:06:35 sarkovy systemd-networkd[1294]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=GetConnectionUnixUser cookie=52 reply_cookie=0 signature=s error-name=n/a error-message=n/a Jan 31 11:06:35 sarkovy systemd-networkd[1294]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.12 path=n/a interface=n/a member=n/a cookie=4294967295 reply_cookie=52 signature=u error-name=n/a error-message=n/a These are the contents of /etc/systemd/network/50-vpn.network: [Match] Name = vpn_* [Link] RequiredForOnline = no ActivationPolicy = up ARP = no [Network] Description = VPN interface DHCP = no DHCPServer = no LinkLocalAddressing = no DefaultRouteOnDevice = no LLMNR = no IPv6AcceptRA = no Bridge = br_lan </blockquote></div> -- <div dir="ltr" class="gmail_signature"><div dir="ltr">Mantas Mikulėnas</div></div>