Manual
Layer 2 Tunnel Protocol Version 3
Information About Layer 2 Tunnel Protocol Version 3
12
Cisco IOS Releases 12.0(29)S and 12.2(25)S
Figure 1 L2TPv3 Operation
In Figure 1, the PE routers R1 and R2 provide L2TPv3 services. The R1 and R2 routers communicate
with each other using a pseudowire over the IP backbone network through a path comprising the
interfaces int1 and int2, the IP network, and interfaces int3 and int4.
In this example, the CE routers R3 and R4 communicate through a pair of Xconnect Ethernet or 802.1q
VLAN interfaces using an L2TPv3 session. The L2TPv3 session tu1 is a pseudowire configured between
interface int1 on R1 and interface int4 on R2. Any packet arriving on interface int1 on R1 is encapsulated
and sent via the pseudowire control channel (tu1) to R2. R2 decapsulates the packet and sends it on
interface int4 to R4. When R4 needs to send a packet to R3, the packet follows the same path in reverse.
Please note the following features regarding L2TPv3 operation:
• All packets received on interface int1 will be forwarded to R4. R3 and R4 cannot detect the
intervening network.
• For Ethernet interfaces, any packet received from LAN1 by R1 on Ethernet interface e1 will be
encapsulated directly in IP and sent via the pseudowire session tu2 to R2 interface e2, where it will
be sent on LAN2.
• A VLAN on an Ethernet interface can be mapped to an L2TPv3 session.
Benefits of Using L2TPv3
L2TPv3 Simplifies Deployment of VPNs
L2TPv3 is an industry-standard Layer 2 tunneling protocol that ensures interoperability among vendors,
increasing customer flexibility and service availability.
L2TPv3 Does Not Require MPLS
With L2TPv3 service providers need not deploy MPLS in the core IP backbone to set up VPNs using
L2TPv3 over the IP backbone, resulting in operational savings and increased revenue.
L2TPv3 Supports Layer 2 Tunneling over IP for Any Payload
L2TPv3 provides enhancements to L2TP to support Layer 2 tunneling of any payload over an IP core
network. L2TPv3 defines the base L2TP protocol as being separate from the Layer 2 payload that is
tunneled.
80653
IP network
LAN1
L2TPv3 tunneled LAN L2TPv3 tunneled LAN
Xconnected
interface
Xconnected
interface
L2TPv3-based
L2 tunnel
PE R1
Pseudowire tu1
Pseudowire tu2
PE R2
e2e1
CE R3
CE R4
int1
int2 int3
int4
LAN2