1. MPLS over L2TPv3 Encapsulation IETF 61

2. 01234567890123456789012345678901 VersionIHLTOSTotal length IdentificationFlagsFragment offset TTL Protocol == 0x73 (L2TP) Header checksum Source IP address (Local address on PE router) Destination IP address (Local address on PE router) Session ID (32 bits) Cookie (32 or 64 bits, Optional) L2TPv3 – Multiservice Tunneling L2TPv3 Encapsulation defined in RFC 3931 (draft-ietf-l2tpext-l2tp-base-14.txt) MPLS over L2TPv3 encapsulation defined in draft-townsley-l2tpv3-mpls-02.txt Payload Frame Relay HDLC Ethernet (VPWS or VPLS) ATM (Cell or Packet) TDM MPLS PPP

3. L2TPv3 Encapsulation Session ID and Cookie (if present) may be signaled, or manually configured. Session ID is used during decapsulation to identify service or session context for L2TPv3. Before processing the L2TPv3 payload, the Cookie returned via the Session ID context lookup and the Cookie in the received packet header are compared to ensure they match. Session ID (32 bits) Cookie (32 or 64 bits, Optional)

4. 01234567890123456789012345678901 VersionIHLTOSTotal length IdentificationFlagsFragment offset TTLProtocol == 0x73 (L2TP)Header checksum Source IP address (Local address on PE router) Destination IP address (Local address on PE router) Session ID (32 bits) Tunnel IP Cookie (32 or 64 bits, Optional) L2TPv3 LabelExpSTTL MPLS over L2TPv3 MPLS PDU MPLS Stack + PDU

5. Alignment with other MPLS tunneling methods Draft-ietf-mpls-in-gre-or-ip-08.txt defines: 1.MPLS over IP 2.MPLS over GRE with “full” header 3.MPLS over GRE with “simplified” header 4.MPLS over IP with IPsec transport mode 5.MPLS over GRE with IPsec transport mode There are a number of common issues when encapsulating MPLS over IP, GRE or L2TPv3 which should continue to be defined in a single location.

6. MPLS over L2TPv3 Specification Any specification defining the MPLS over L2TPv3 encapsulation should include an applicability section similar to that for MPLS over IP vs. MPLS over GRE vs. MPLS over IPsec. For example, –Two routers may already be “adjacent” over an L2TPv3 tunnel for other services outside of MPLS- based services –Implementation considerations may dictate the use of MPLS over L2TPv3. For example, a hardware device might be better equipped to handle L2TPv3, utilize the L2TPv3 Session ID to aid in distributed processing of different services, etc. –L2TPv3 Cookie allows a decapsulating PE to perform a context lookup validation based on the L2TPv3 session or service

7. Next Steps? Add L2TPv3 to the list of methods for tunneling MPLS traffic Create a short and concise (5 pages or less!) MPLS over L2TPv3 WG draft with an appropriate applicability statement and reference to draft-ietf-mpls-in-gre-or-ip-08.txt for common IP encapsulation issues draft-townsley-l2tpv3-mpls-02.txt could be a start.

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