Static L2Tpv3 Sessions; Dynamic L2Tpv3 Sessions; Local Switching - Cisco CRS Configuration Manual

L2TPv3 Features
• Site of origin for BGP VPNs
• IPSec Mapping to L2TPv3
•
• Like-to-Like Pseudowires

Static L2TPv3 Sessions

Typically, the L2TP control plane is responsible for negotiating session parameters (such as the session ID
or the cookie) to set up the session; however, some IP networks require sessions to be configured so that no
signaling is required for session establishment. Therefore, you can set up static L2TPv3 sessions for a PE
router by configuring fixed values for the fields in the L2TP data header. A static L2TPv3 session allows the
PE to tunnel L2 traffic as soon as the AC to which the session is bound comes up.
Note In an L2TPv3 static session, you can still run the L2TP control-channel to perform peer authentication
and dead-peer detection. If the L2TP control-channel cannot be established or is torn down because of a
hello failure, the static session is also torn down.

Dynamic L2TPv3 Sessions

A dynamic L2TP session is established through the exchange of control messages containing attribute-value
pair (AVP). Each AVP contains information about the nature of the L2 link being forwarded: including the
payload type, virtual circuit (VC) ID, and so on.
Multiple L2TP sessions can exist between a pair of PEs, and can be maintained by a single control-channel.
Session IDs and cookies are dynamically generated and exchanged as part of a dynamic session setup.

Local Switching

An AC to AC cross-connect, also called local switching, is a building block of L2VPN that allows frames to
switch between two different ACs on the same PE. PE (see figure below).
You must configure separate IP addresses for each cross-connect statement on the Carrier Edge router.
The following configurations are supported for local switching:
• Port-to-Port
• Dot1q-to-Dot1q
• QinQ-to-QinQ
• QinAny-to-QinAny
• Dot1q-to-QinQ
• QinQ-to-Dot1q
• QinQ-to-QinAny
• QinAny-to-QinQ
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
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Implementing Layer 2 Tunnel Protocol Version 3