NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | INTEROPERABILITY | SEE ALSO | AUTHOR | COLOPHON

IP-L2TP(8)                          Linux                         IP-L2TP(8)

NAME         top

       ip-l2tp - L2TPv3 static unmanaged tunnel configuration

SYNOPSIS         top

       ip [ OPTIONS ] l2tp  { COMMAND | help }

       ip l2tp add tunnel
               remote ADDR local ADDR
               tunnel_id ID peer_tunnel_id ID
               [ encap { ip | udp } ]
               [ udp_sport PORT  ] [ udp_dport PORT  ]
               [ udp_csum { on | off } ]
               [ udp6_csum_tx { on | off } ]
               [ udp6_csum_rx { on | off } ]
       ip l2tp add session [ name NAME  ]
               tunnel_id ID session_id ID peer_session_id ID
               [ cookie HEXSTR  ] [ peer_cookie HEXSTR  ]
               [ l2spec_type { none | default } ]
               [ seq { none | send | recv | both } ]
               [ offset OFFSET  ] [ peer_offset OFFSET  ]
       ip l2tp del tunnel tunnel_id ID
       ip l2tp del session tunnel_id ID session_id ID
       ip l2tp show tunnel [ tunnel_id ID ]
       ip l2tp show session [ tunnel_id ID.B ] [ session_id ID ]
       NAME := STRING
       ADDR := { IP_ADDRESS | any }
       PORT := { NUMBER }
       ID := { NUMBER }
       HEXSTR := { 8 or 16 hex digits (4 / 8 bytes) }

DESCRIPTION         top

       The ip l2tp commands are used to establish static, or so-called
       unmanaged L2TPv3 ethernet tunnels. For unmanaged tunnels, there is no
       L2TP control protocol so no userspace daemon is required - tunnels
       are manually created by issuing commands at a local system and at a
       remote peer.

       L2TPv3 is suitable for Layer-2 tunneling. Static tunnels are useful
       to establish network links across IP networks when the tunnels are
       fixed. L2TPv3 tunnels can carry data of more than one session. Each
       session is identified by a session_id and its parent tunnel's
       tunnel_id. A tunnel must be created before a session can be created
       in the tunnel.

       When creating an L2TP tunnel, the IP address of the remote peer is
       specified, which can be either an IPv4 or IPv6 address. The local IP
       address to be used to reach the peer must also be specified. This is
       the address on which the local system will listen for and accept
       received L2TP data packets from the peer.

       L2TPv3 defines two packet encapsulation formats: UDP or IP. UDP
       encapsulation is most common. IP encapsulation uses a dedicated IP
       protocol value to carry L2TP data without the overhead of UDP. Use IP
       encapsulation only when there are no NAT devices or firewalls in the
       network path.

       When an L2TPv3 ethernet session is created, a virtual network
       interface is created for the session, which must then be configured
       and brought up, just like any other network interface. When data is
       passed through the interface, it is carried over the L2TP tunnel to
       the peer. By configuring the system's routing tables or adding the
       interface to a bridge, the L2TP interface is like a virtual wire
       (pseudowire) connected to the peer.

       Establishing an unmanaged L2TPv3 ethernet pseudowire involves
       manually creating L2TP contexts on the local system and at the peer.
       Parameters used at each site must correspond or no data will be
       passed. No consistency checks are possible since there is no control
       protocol used to establish unmanaged L2TP tunnels. Once the virtual
       network interface of a given L2TP session is configured and enabled,
       data can be transmitted, even if the peer isn't yet configured. If
       the peer isn't configured, the L2TP data packets will be discarded by
       the peer.

       To establish an unmanaged L2TP tunnel, use l2tp add tunnel and l2tp
       add session commands described in this document. Then configure and
       enable the tunnel's virtual network interface, as required.

       Note that unmanaged tunnels carry only ethernet frames. If you need
       to carry PPP traffic (L2TPv2) or your peer doesn't support unmanaged
       L2TPv3 tunnels, you will need an L2TP server which implements the
       L2TP control protocol. The L2TP control protocol allows dynamic L2TP
       tunnels and sessions to be established and provides for detecting and
       acting upon network failures.

   ip l2tp add tunnel - add a new tunnel
       tunnel_id ID
              set the tunnel id, which is a 32-bit integer value. Uniquely
              identifies the tunnel. The value used must match the
              peer_tunnel_id value being used at the peer.

       peer_tunnel_id ID
              set the peer tunnel id, which is a 32-bit integer value
              assigned to the tunnel by the peer. The value used must match
              the tunnel_id value being used at the peer.

       remote ADDR
              set the IP address of the remote peer. May be specified as an
              IPv4 address or an IPv6 address.

       local ADDR
              set the IP address of the local interface to be used for the
              tunnel. This address must be the address of a local interface.
              May be specified as an IPv4 address or an IPv6 address.

       encap ENCAP
              set the encapsulation type of the tunnel.
              Valid values for encapsulation are: udp, ip.

       udp_sport PORT
              set the UDP source port to be used for the tunnel. Must be
              present when udp encapsulation is selected. Ignored when ip
              encapsulation is selected.

       udp_dport PORT
              set the UDP destination port to be used for the tunnel. Must
              be present when udp encapsulation is selected. Ignored when ip
              encapsulation is selected.

       udp_csum STATE
              (IPv4 only) control if IPv4 UDP checksums should be calculated
              and checked for the encapsulating UDP packets, when UDP
              encapsulating is selected.  Default is off.
              Valid values are: on, off.

       udp6_csum_tx STATE
              (IPv6 only) control if IPv6 UDP checksums should be calculated
              for encapsulating UDP packets, when UDP encapsulating is
              selected.  Default is on.
              Valid values are: on, off.

       udp6_csum_rx STATE
              (IPv6 only) control if IPv6 UDP checksums should be checked
              for the encapsulating UDP packets, when UDP encapsulating is
              selected.  Default is on.
              Valid values are: on, off.

   ip l2tp del tunnel - destroy a tunnel
       tunnel_id ID
              set the tunnel id of the tunnel to be deleted. All sessions
              within the tunnel must be deleted first.

   ip l2tp show tunnel - show information about tunnels
       tunnel_id ID
              set the tunnel id of the tunnel to be shown. If not specified,
              information about all tunnels is printed.

   ip l2tp add session - add a new session to a tunnel
       name NAME
              sets the session network interface name. Default is l2tpethN.

       tunnel_id ID
              set the tunnel id, which is a 32-bit integer value. Uniquely
              identifies the tunnel into which the session will be created.
              The tunnel must already exist.

       session_id ID
              set the session id, which is a 32-bit integer value. Uniquely
              identifies the session being created. The value used must
              match the peer_session_id value being used at the peer.

       peer_session_id ID
              set the peer session id, which is a 32-bit integer value
              assigned to the session by the peer. The value used must match
              the session_id value being used at the peer.

       cookie HEXSTR
              sets an optional cookie value to be assigned to the session.
              This is a 4 or 8 byte value, specified as 8 or 16 hex digits,
              e.g. 014d3636deadbeef. The value must match the peer_cookie
              value set at the peer. The cookie value is carried in L2TP
              data packets and is checked for expected value at the peer.
              Default is to use no cookie.

       peer_cookie HEXSTR
              sets an optional peer cookie value to be assigned to the
              session. This is a 4 or 8 byte value, specified as 8 or 16 hex
              digits, e.g. 014d3636deadbeef. The value must match the cookie
              value set at the peer. It tells the local system what cookie
              value to expect to find in received L2TP packets. Default is
              to use no cookie.

       l2spec_type L2SPECTYPE
              set the layer2specific header type of the session.
              Valid values are: none, default.

       seq SEQ
              controls sequence numbering to prevent or detect out of order
              packets.  send puts a sequence number in the default
              layer2specific header of each outgoing packet.  recv reorder
              packets if they are received out of order.  Default is none.
              Valid values are: none, send, recv, both.

       offset OFFSET
              sets the byte offset from the L2TP header where user data
              starts in transmitted L2TP data packets. This is hardly ever
              used. If set, the value must match the peer_offset value used
              at the peer. Default is 0.

       peer_offset OFFSET
              sets the byte offset from the L2TP header where user data
              starts in received L2TP data packets. This is hardly ever
              used. If set, the value must match the offset value used at
              the peer. Default is 0.

   ip l2tp del session - destroy a session
       tunnel_id ID
              set the tunnel id in which the session to be deleted is
              located.

       session_id ID
              set the session id of the session to be deleted.

   ip l2tp show session - show information about sessions
       tunnel_id ID
              set the tunnel id of the session(s) to be shown. If not
              specified, information about sessions in all tunnels is
              printed.

       session_id ID
              set the session id of the session to be shown. If not
              specified, information about all sessions is printed.

EXAMPLES         top

   Setup L2TP tunnels and sessions
       site-A:# ip l2tp add tunnel tunnel_id 3000 peer_tunnel_id 4000 \
                  encap udp local 1.2.3.4 remote 5.6.7.8 \
                  udp_sport 5000 udp_dport 6000
       site-A:# ip l2tp add session tunnel_id 3000 session_id 1000 \
                  peer_session_id 2000

       site-B:# ip l2tp add tunnel tunnel_id 4000 peer_tunnel_id 3000 \
                  encap udp local 5.6.7.8 remote 1.2.3.4 \
                  udp_sport 6000 udp_dport 5000
       site-B:# ip l2tp add session tunnel_id 4000 session_id 2000 \
                  peer_session_id 1000

       site-A:# ip link set l2tpeth0 up mtu 1488

       site-B:# ip link set l2tpeth0 up mtu 1488

       Notice that the IP addresses, UDP ports and tunnel / session ids are
       matched and reversed at each site.

   Configure as IP interfaces
       The two interfaces can be configured with IP addresses if only IP
       data is to be carried. This is perhaps the simplest configuration.

       site-A:# ip addr add 10.42.1.1 peer 10.42.1.2 dev l2tpeth0

       site-B:# ip addr add 10.42.1.2 peer 10.42.1.1 dev l2tpeth0

       site-A:# ping 10.42.1.2

       Now the link should be usable. Add static routes as needed to have
       data sent over the new link.

   Configure as bridged interfaces
       To carry non-IP data, the L2TP network interface is added to a bridge
       instead of being assigned its own IP address, using standard Linux
       utilities. Since raw ethernet frames are then carried inside the
       tunnel, the MTU of the L2TP interfaces must be set to allow space for
       those headers.

       site-A:# ip link set l2tpeth0 up mtu 1446
       site-A:# ip link add br0 type bridge
       site-A:# ip link set l2tpeth0 master br0
       site-A:# ip link set eth0 master br0
       site-A:# ip link set br0 up

       If you are using VLANs, setup a bridge per VLAN and bridge each VLAN
       over a separate L2TP session. For example, to bridge VLAN ID 5 on
       eth1 over an L2TP pseudowire:

       site-A:# ip link set l2tpeth0 up mtu 1446
       site-A:# ip link add brvlan5 type bridge
       site-A:# ip link set l2tpeth0.5 master brvlan5
       site-A:# ip link set eth1.5 master brvlan5
       site-A:# ip link set brvlan5 up

       Adding the L2TP interface to a bridge causes the bridge to forward
       traffic over the L2TP pseudowire just like it forwards over any other
       interface. The bridge learns MAC addresses of hosts attached to each
       interface and intelligently forwards frames from one bridge port to
       another. IP addresses are not assigned to the l2tpethN interfaces. If
       the bridge is correctly configured at both sides of the L2TP
       pseudowire, it should be possible to reach hosts in the peer's
       bridged network.

       When raw ethernet frames are bridged across an L2TP tunnel, large
       frames may be fragmented and forwarded as individual IP fragments to
       the recipient, depending on the MTU of the physical interface used by
       the tunnel. When the ethernet frames carry protocols which are
       reassembled by the recipient, like IP, this isn't a problem. However,
       such fragmentation can cause problems for protocols like PPPoE where
       the recipient expects to receive ethernet frames exactly as
       transmitted. In such cases, it is important that frames leaving the
       tunnel are reassembled back into a single frame before being
       forwarded on. To do so, enable netfilter connection tracking
       (conntrack) or manually load the Linux netfilter defrag modules at
       each tunnel endpoint.

       site-A:# modprobe nf_defrag_ipv4

       site-B:# modprobe nf_defrag_ipv4

       If L2TP is being used over IPv6, use the IPv6 defrag module.

INTEROPERABILITY         top

       Unmanaged (static) L2TPv3 tunnels are supported by some network
       equipment equipment vendors such as Cisco.

       In Linux, L2TP Hello messages are not supported in unmanaged tunnels.
       Hello messages are used by L2TP clients and servers to detect link
       failures in order to automate tearing down and reestablishing dynamic
       tunnels. If a non-Linux peer supports Hello messages in unmanaged
       tunnels, it must be turned off to interoperate with Linux.

       Linux defaults to use the Default Layer2SpecificHeader type as
       defined in the L2TPv3 protocol specification, RFC3931. This setting
       must be consistent with that configured at the peer. Some vendor
       implementations (e.g. Cisco) default to use a Layer2SpecificHeader
       type of None.

SEE ALSO         top

       ip(8)

AUTHOR         top

       James Chapman <jchapman@katalix.com>

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
       on 2017-09-15.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-to-
       date source for the page, or you have corrections or improvements to
       the information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

iproute2                         19 Apr 2012                      IP-L2TP(8)

Pages that refer to this page: ip(8)