1IP-L2TP(8) Linux IP-L2TP(8)
2
6 ip-l2tp - L2TPv3 static unmanaged tunnel configuration
7
9 ip [ OPTIONS ] l2tp { COMMAND | help }
10 ip l2tp add tunnel
12 remote ADDR local ADDR
13 tunnel_id ID peer_tunnel_id ID
14 [ encap { ip | udp } ]
15 [ udp_sport PORT ] [ udp_dport PORT ]
16 [ udp_csum { on | off } ]
17 [ udp6_csum_tx { on | off } ]
18 [ udp6_csum_rx { on | off } ]
19 ip l2tp add session [ name NAME ]
20 tunnel_id ID session_id ID peer_session_id ID
21 [ cookie HEXSTR ] [ peer_cookie HEXSTR ]
22 [ l2spec_type { none | default } ]
23 [ seq { none | send | recv | both } ]
24 ip l2tp del tunnel tunnel_id ID
25 ip l2tp del session tunnel_id ID session_id ID
26 ip l2tp show tunnel [ tunnel_id ID ]
27 ip l2tp show session [ tunnel_id ID.B ] [ session_id ID ]
28 NAME := STRING
29 ADDR := { IP_ADDRESS | any }
30 PORT := { NUMBER }
31 ID := { NUMBER }
32 HEXSTR := { 8 or 16 hex digits (4 / 8 bytes) }
33
35 The ip l2tp commands are used to establish static, or so-called unman‐
36 aged L2TPv3 ethernet tunnels. For unmanaged tunnels, there is no L2TP
37 control protocol so no userspace daemon is required - tunnels are manu‐
38 ally created by issuing commands at a local system and at a remote
39 peer.
40 L2TPv3 is suitable for Layer-2 tunneling. Static tunnels are useful to
42 establish network links across IP networks when the tunnels are fixed.
43 L2TPv3 tunnels can carry data of more than one session. Each session is
44 identified by a session_id and its parent tunnel's tunnel_id. A tunnel
45 must be created before a session can be created in the tunnel.
46 When creating an L2TP tunnel, the IP address of the remote peer is
48 specified, which can be either an IPv4 or IPv6 address. The local IP
49 address to be used to reach the peer must also be specified. This is
50 the address on which the local system will listen for and accept
51 received L2TP data packets from the peer.
52 L2TPv3 defines two packet encapsulation formats: UDP or IP. UDP encap‐
54 sulation is most common. IP encapsulation uses a dedicated IP protocol
55 value to carry L2TP data without the overhead of UDP. Use IP encapsula‐
56 tion only when there are no NAT devices or firewalls in the network
57 path.
58 When an L2TPv3 ethernet session is created, a virtual network interface
60 is created for the session, which must then be configured and brought
61 up, just like any other network interface. When data is passed through
62 the interface, it is carried over the L2TP tunnel to the peer. By con‐
63 figuring the system's routing tables or adding the interface to a
64 bridge, the L2TP interface is like a virtual wire (pseudowire) con‐
65 nected to the peer.
66 Establishing an unmanaged L2TPv3 ethernet pseudowire involves manually
68 creating L2TP contexts on the local system and at the peer. Parameters
69 used at each site must correspond or no data will be passed. No consis‐
70 tency checks are possible since there is no control protocol used to
71 establish unmanaged L2TP tunnels. Once the virtual network interface of
72 a given L2TP session is configured and enabled, data can be transmit‐
73 ted, even if the peer isn't yet configured. If the peer isn't config‐
74 ured, the L2TP data packets will be discarded by the peer.
75 To establish an unmanaged L2TP tunnel, use l2tp add tunnel and l2tp add
77 session commands described in this document. Then configure and enable
78 the tunnel's virtual network interface, as required.
79 Note that unmanaged tunnels carry only ethernet frames. If you need to
81 carry PPP traffic (L2TPv2) or your peer doesn't support unmanaged
82 L2TPv3 tunnels, you will need an L2TP server which implements the L2TP
83 control protocol. The L2TP control protocol allows dynamic L2TP tunnels
84 and sessions to be established and provides for detecting and acting
85 upon network failures.
86 ip l2tp add tunnel - add a new tunnel
88 tunnel_id ID
89 set the tunnel id, which is a 32-bit integer value. Uniquely
90 identifies the tunnel. The value used must match the peer_tun‐
91 nel_id value being used at the peer.
92 peer_tunnel_id ID
94 set the peer tunnel id, which is a 32-bit integer value assigned
95 to the tunnel by the peer. The value used must match the tun‐
96 nel_id value being used at the peer.
97 remote ADDR
99 set the IP address of the remote peer. May be specified as an
100 IPv4 address or an IPv6 address.
101 local ADDR
103 set the IP address of the local interface to be used for the
104 tunnel. This address must be the address of a local interface.
105 May be specified as an IPv4 address or an IPv6 address.
106 encap ENCAP
108 set the encapsulation type of the tunnel.
109 Valid values for encapsulation are: udp, ip.
110 udp_sport PORT
112 set the UDP source port to be used for the tunnel. Must be
113 present when udp encapsulation is selected. Ignored when ip
114 encapsulation is selected.
115 udp_dport PORT
117 set the UDP destination port to be used for the tunnel. Must be
118 present when udp encapsulation is selected. Ignored when ip
119 encapsulation is selected.
120 udp_csum STATE
122 (IPv4 only) control if IPv4 UDP checksums should be calculated
123 and checked for the encapsulating UDP packets, when UDP encapsu‐
124 lating is selected. Default is off.
125 Valid values are: on, off.
126 udp6_csum_tx STATE
128 (IPv6 only) control if IPv6 UDP checksums should be calculated
129 for encapsulating UDP packets, when UDP encapsulating is
130 selected. Default is on.
131 Valid values are: on, off.
132 udp6_csum_rx STATE
134 (IPv6 only) control if IPv6 UDP checksums should be checked for
135 the encapsulating UDP packets, when UDP encapsulating is
136 selected. Default is on.
137 Valid values are: on, off.
138 ip l2tp del tunnel - destroy a tunnel
140 tunnel_id ID
141 set the tunnel id of the tunnel to be deleted. All sessions
142 within the tunnel must be deleted first.
143 ip l2tp show tunnel - show information about tunnels
145 tunnel_id ID
146 set the tunnel id of the tunnel to be shown. If not specified,
147 information about all tunnels is printed.
148 ip l2tp add session - add a new session to a tunnel
150 name NAME
151 sets the session network interface name. Default is l2tpethN.
152 tunnel_id ID
154 set the tunnel id, which is a 32-bit integer value. Uniquely
155 identifies the tunnel into which the session will be created.
156 The tunnel must already exist.
157 session_id ID
159 set the session id, which is a 32-bit integer value. Uniquely
160 identifies the session being created. The value used must match
161 the peer_session_id value being used at the peer.
162 peer_session_id ID
164 set the peer session id, which is a 32-bit integer value
165 assigned to the session by the peer. The value used must match
166 the session_id value being used at the peer.
167 cookie HEXSTR
169 sets an optional cookie value to be assigned to the session.
170 This is a 4 or 8 byte value, specified as 8 or 16 hex digits,
171 e.g. 014d3636deadbeef. The value must match the peer_cookie
172 value set at the peer. The cookie value is carried in L2TP data
173 packets and is checked for expected value at the peer. Default
174 is to use no cookie.
175 peer_cookie HEXSTR
177 sets an optional peer cookie value to be assigned to the ses‐
178 sion. This is a 4 or 8 byte value, specified as 8 or 16 hex dig‐
179 its, e.g. 014d3636deadbeef. The value must match the cookie
180 value set at the peer. It tells the local system what cookie
181 value to expect to find in received L2TP packets. Default is to
182 use no cookie.
183 l2spec_type L2SPECTYPE
185 set the layer2specific header type of the session.
186 Valid values are: none, default.
187 seq SEQ
189 controls sequence numbering to prevent or detect out of order
190 packets. send puts a sequence number in the default layer2spe‐
191 cific header of each outgoing packet. recv reorder packets if
192 they are received out of order. Default is none.
193 Valid values are: none, send, recv, both.
194 ip l2tp del session - destroy a session
196 tunnel_id ID
197 set the tunnel id in which the session to be deleted is located.
198 session_id ID
200 set the session id of the session to be deleted.
201 ip l2tp show session - show information about sessions
203 tunnel_id ID
204 set the tunnel id of the session(s) to be shown. If not speci‐
205 fied, information about sessions in all tunnels is printed.
206 session_id ID
208 set the session id of the session to be shown. If not specified,
209 information about all sessions is printed.
210
212 Setup L2TP tunnels and sessions
213 site-A:# ip l2tp add tunnel tunnel_id 3000 peer_tunnel_id 4000 \
214 encap udp local 1.2.3.4 remote 5.6.7.8 \
215 udp_sport 5000 udp_dport 6000
216 site-A:# ip l2tp add session tunnel_id 3000 session_id 1000 \
217 peer_session_id 2000
218 site-B:# ip l2tp add tunnel tunnel_id 4000 peer_tunnel_id 3000 \
220 encap udp local 5.6.7.8 remote 1.2.3.4 \
221 udp_sport 6000 udp_dport 5000
222 site-B:# ip l2tp add session tunnel_id 4000 session_id 2000 \
223 peer_session_id 1000
224 site-A:# ip link set l2tpeth0 up mtu 1488
226 site-B:# ip link set l2tpeth0 up mtu 1488
228 Notice that the IP addresses, UDP ports and tunnel / session ids are
230 matched and reversed at each site.
231 Configure as IP interfaces
233 The two interfaces can be configured with IP addresses if only IP data
234 is to be carried. This is perhaps the simplest configuration.
235 site-A:# ip addr add 10.42.1.1 peer 10.42.1.2 dev l2tpeth0
237 site-B:# ip addr add 10.42.1.2 peer 10.42.1.1 dev l2tpeth0
239 site-A:# ping 10.42.1.2
241 Now the link should be usable. Add static routes as needed to have data
243 sent over the new link.
244 Configure as bridged interfaces
246 To carry non-IP data, the L2TP network interface is added to a bridge
247 instead of being assigned its own IP address, using standard Linux
248 utilities. Since raw ethernet frames are then carried inside the tun‐
249 nel, the MTU of the L2TP interfaces must be set to allow space for
250 those headers.
251 site-A:# ip link set l2tpeth0 up mtu 1446
253 site-A:# ip link add br0 type bridge
254 site-A:# ip link set l2tpeth0 master br0
255 site-A:# ip link set eth0 master br0
256 site-A:# ip link set br0 up
257 If you are using VLANs, setup a bridge per VLAN and bridge each VLAN
259 over a separate L2TP session. For example, to bridge VLAN ID 5 on eth1
260 over an L2TP pseudowire:
261 site-A:# ip link set l2tpeth0 up mtu 1446
263 site-A:# ip link add brvlan5 type bridge
264 site-A:# ip link set l2tpeth0.5 master brvlan5
265 site-A:# ip link set eth1.5 master brvlan5
266 site-A:# ip link set brvlan5 up
267 Adding the L2TP interface to a bridge causes the bridge to forward
269 traffic over the L2TP pseudowire just like it forwards over any other
270 interface. The bridge learns MAC addresses of hosts attached to each
271 interface and intelligently forwards frames from one bridge port to
272 another. IP addresses are not assigned to the l2tpethN interfaces. If
273 the bridge is correctly configured at both sides of the L2TP pseu‐
274 dowire, it should be possible to reach hosts in the peer's bridged net‐
275 work.
276 When raw ethernet frames are bridged across an L2TP tunnel, large
278 frames may be fragmented and forwarded as individual IP fragments to
279 the recipient, depending on the MTU of the physical interface used by
280 the tunnel. When the ethernet frames carry protocols which are reassem‐
281 bled by the recipient, like IP, this isn't a problem. However, such
282 fragmentation can cause problems for protocols like PPPoE where the
283 recipient expects to receive ethernet frames exactly as transmitted. In
284 such cases, it is important that frames leaving the tunnel are reassem‐
285 bled back into a single frame before being forwarded on. To do so,
286 enable netfilter connection tracking (conntrack) or manually load the
287 Linux netfilter defrag modules at each tunnel endpoint.
288 site-A:# modprobe nf_defrag_ipv4
290 site-B:# modprobe nf_defrag_ipv4
292 If L2TP is being used over IPv6, use the IPv6 defrag module.
294
296 Unmanaged (static) L2TPv3 tunnels are supported by some network equip‐
297 ment equipment vendors such as Cisco.
298 In Linux, L2TP Hello messages are not supported in unmanaged tunnels.
300 Hello messages are used by L2TP clients and servers to detect link
301 failures in order to automate tearing down and reestablishing dynamic
302 tunnels. If a non-Linux peer supports Hello messages in unmanaged tun‐
303 nels, it must be turned off to interoperate with Linux.
304 Linux defaults to use the Default Layer2SpecificHeader type as defined
306 in the L2TPv3 protocol specification, RFC3931. This setting must be
307 consistent with that configured at the peer. Some vendor implementa‐
308 tions (e.g. Cisco) default to use a Layer2SpecificHeader type of None.
309
311 ip(8)
312
314 James Chapman <jchapman@katalix.com>
315iproute2 19 Apr 2012 IP-L2TP(8)