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NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | INTEROPERABILITY | SEE ALSO | AUTHOR | COLOPHON |
IP-L2TP(8) Linux IP-L2TP(8)
ip-l2tp - L2TPv3 static unmanaged tunnel configuration
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) }
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.
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.
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.
ip(8)
James Chapman <jchapman@katalix.com>
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 2017-07-05. If you discover any rendering problems in this HTML
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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)