Advanced Internet Protocols, Services, and Applications by Eiji Oki & Roberto Rojas-Cessa & Mallikarjun Tatipamula & Christian Vogt

Author:Eiji Oki & Roberto Rojas-Cessa & Mallikarjun Tatipamula & Christian Vogt
Language: eng
Format: epub, pdf
Publisher: Wiley
Published: 2012-02-28T16:00:00+00:00

9.1.4 IP-Only Layer-2 Virtual Private Network

This is a point-to-point or point-to-multipoint IP-only service over an IP or MPLS-enabled PSN. It is similar to VPWS in that it supports a variety of link-layer protocols on the ACs, including Frame Relay, ATM, Ethernet, and PPP.

The interconnected systems may be LAN switches. Furthermore, using IP hosts or IP routers, certain simplifications to the operation of the VPLS can be possible. This simplified type of VPLS has been called an IP-only LAN service (IPLS) in recent IETF drafts. In an IPLS, as in a VPLS, LAN interfaces are run in promiscuous mode, and frames are forwarded based on their destination MAC addresses. However, the maintenance of the MAC forwarding tables is done via signaling rather than via the MAC address learning procedures specified in IEEE 802.1D. IPLS is an example of a Layer-2 and Layer-3 VPN, as interlayer crossing of protocols is used.

Functions of IP-only L2VPN include the following:

IP-only L2VPNs are different from both VPLS and VPWS because unicast Layer-2 frames containing IP data packets, either IPv4 or IPv6, are de-encapsulated leaving only the IP data packet to be transmitted over the PSN.

An IP-only L2VPN service also differs from L3VPN service since no routing protocol operates between the PE and CE. Furthermore, connectivity from CE to CE is provided via an emulated Layer-2 service over the PSN, which results in the CEs appearing to be directly attached to each other at Layer 2. The WG will address two specific types of IP-only L2VPN: 1. Those with ACs that use the same Layer-2 framing at all attachment points in the same L2VPN.

2. Those with ACs that use different Layer-2 framing at various attachment points in the same L2VPN.

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