What should I be aware of when using the Layer 2 Tunneling Protocol (L2TP) client-server protocol to allow the Point-to-Point Protocol (PPP) to be tunneled across a network?
You should be aware of the following items:
- L2TP Sessions and Subscriber Access - There is a one-to-one relationship between established Layer 2 Tunneling Protocol (L2TP) sessions and their associated Point-to-Point Protocol (PPP) connections. For more information, click L2TP Terminology.
- Tunnel Switching Actions - Layer 2 Tunneling Protocol (L2TP) attribute-value pairs (AVPs) that have their attribute values hidden are always regenerated at the switching boundary. The value is decoded and sent in clear text when the packet is forwarded to the remote L2TP network server (LNS). For more information, click Tunnel Switching Actions for L2TP AVPs at the Switching Boundary.
- Configuring L2TP Tunnel Switching - A tunnel group with a tunnel switch profile must also contain a dynamic profile because tunnel switching supports only dynamic subscribers. For more information, click Configuring L2TP Tunnel Switching.
- LAC Tunnel Selection:
- Zero (0) is the highest level of preference; this is the most-preferred level. Preference indicates the order in which the L2TP access concentrator (LAC) attempts to connect to the destinations specified for a domain.
- More than one tunnel might be able to reach a destination, and those tunnels can have the same preference level or different preference levels.
- Weighted load balancing and destination-equal load balancing are mutually exclusive. You can enable only one or the other.
- Tunnel selection and session distribution are probability based; the load is not strictly distributed according to weight.
For more information, click LAC Tunnel Selection Overview.
- Fallback for Connection Speeds - For both Gigabit Ethernet (ge) and 10-Gigabit Ethernet (xe) interfaces, the port speed value is set to 1,000,000,000. For aggregated Ethernet (ae) interfaces, the port speed value is set to 0. The port speed value for all these interface types is reported in both (attribute-value pair) AVP 24 and AVP 38. For more information, click Transmission of Tx Connect-Speed and Rx Connect-Speed AVPs from LAC to LNS.
- PPP Attributes and L2TP Subscribers - Changes to the keepalive interval in a user group profile affect only new Layer 2 Tunneling Protocol (L2TP) sessions that come up after the change. Existing sessions are not affected. For more information, click Applying PPP Attributes to L2TP LNS Subscribers with a User Group Profile.
- Configuring L2TP LNS Peer Interface - On MX Series routers, you must configure the peer interface on a Modular Port Concentrator (MPC). For more information, click Configuring the L2TP LNS Peer Interface.
- Configuring L2TP Tunnel Group - You can create up to 256 tunnel groups. For more information, click Configuring an L2TP Tunnel Group for LNS Sessions with Inline Services Interfaces.
For more information, click Broadband Subscriber Access Protocols Feature Guide.