Provided by: iproute2_4.3.0-1ubuntu3_i386 bug

NAME

       ip-l2tp - L2TPv3 static unmanaged tunnel configuration

SYNOPSIS

       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  ]
       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 } ]
               [ 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 ] [ session_id ID ]
       NAME := STRING
       ADDR := { IP_ADDRESS }
       PORT := { NUMBER }
       ID := { NUMBER }
       HEXSTR := { 8 or 16 hex digits (4 / 8 bytes) }

DESCRIPTION

       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
       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. 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.

   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, udp.

       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

   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

       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

       ip(8)

AUTHOR

       James Chapman <jchapman@katalix.com>