Network Working Group Albert J. Tian Internet Draft Naiming Shen Expiration Date: Jan 2005 Redback Networks July 2004 Loose Segment Optimization in Explicit Paths draft-tian-rsvp-loose-seg-opt-00.txt 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. Abstract RSVP-TE [RSVPTE] can signal explicit paths with loose or strict hops in a MPLS network. Using loose hops can shorten the ERO, but can not reduce the overhead associated with an RSVP signaled LSP since path states are still created on every hop along the path. In this paper, we propose a mechanism that can reduce the signaling and maintenance overhead associated with loose hops in an RSVP signaled LSP in an LDP enabled network. The mechanism can also be generalized to work with other tunneling technologies such as GRE or IP-in-IP. Tian & Shen [Page 1] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 3. Introduction A loose hop in an explicit path means the actual path for that loose segment is not pre-determined and may traverse one or more intermediate nodes. In many cases where the the ERO is the only requirement, the path is determined by routing. LDP on the other hand builds LSPs that follow routing. This means the actual path for a loose segment in some explicitly path will be the same as that of an LDP LSP whose egress matches prefix specified in the loose hop. If the LDP LSP can satisfy the requirement of the RSVP loose hop, in other words, the RSVP LSP does not have QoS or other requirements, then we can optimize the RSVP LSP by tunneling control and data traffic directly from the starting node to the ending node of the loose segment through an LDP LSP. Forming Forwarding Adjacency out of a TE LSP and nesting other LSPs into the TE LSP by using label stack construct is a well established concept in GMPLS [HIER-LSP]. Here we are essentially proposing to form "Soft Forwarding Adjacencies" (Soft FAs) out of LDP LSPs and establish RSVP LSPs across LDP LSPs using label stacking. Soft FAs are similar to FAs in that they can be treated as a link to forward control and data traffic. They are different from the FAs in that they are more dynamic, do not have QoS guarantees, and are not advertised to ISIS/OSPF component for path computation. It is also possible to form soft FAs over other tunneling technologies such as GRE or IP-in-IP instead of LDP LSPs. The mechanism is essentially the same. Since LDP LSPs and GRE or IP-in-IP tunnels do not support resource reservation, RSVP LSPs nested inside soft FAs usually can not support resource reservation. One primary application of the loose hop optimization is in the area of IP/LDP fast re-route. RSVP-TE can be used to signal a repair path to protect IP/LDP destinations from link or node failures. Since there is in general no QoS requirement on the original traffic, there is also no QoS requirement on the repair paths. To protect the network from all possible node or link failures, a large number of repair paths need to be established. Therefore it is very important to reduce the per repair path overhead. The loose segment optimization can achieve just that. Tian & Shen [Page 2] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 4. RSVP Extensions A new flag in Session Attribute Object is introduced to indicate Loose Hop Optimization using Soft FAs is desired. The Session Attribute Object is defined in section 4.7 of [RSVPTE]. Flags 0x10 O-bit. Loose Hop Optimization desired. This flag indicates that Loose Hop Optimization using soft FAs is desired. 5. Conditions for Optimization The optimization is performed at the starting and ending node of a loose segment. The starting node of a loose segment in an explicit path is the first node that evaluates the corresponding loose subobject in the ERO. The ending node of a loose segment in an explicit path is the node that contains the prefix in the corresponding subobject in the ERO, or is the egress node of the explicit path. When the starting node of a loose segment evaluates the corresponding subobject in the ERO, if all of the following conditions hold, then the loose hop optimization can be performed: 1) The LSP Optimization Object is present in the PATH message and the O-bit is set, 2) There is an active soft FA whose egress is the exact match for the nexthop address, which is either the prefix in the corresponding subobject in the ERO, or the egress address of the RSVP LSP. 3) The matching soft FA satisfies all the requirements of the RSVP LSP. 4) The matching soft FA satisfies a minimum span requirement set in local configuration. Tian & Shen [Page 3] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 6. Optimization for a Loose Segment 6.1. Head End Node of the RSVP LSP When the head end of an RSVP LSP wants to optimize the loose segment using LDP LSP, then it SHOULD include the LSP Optimization Object in the PATH message with the O-bit set. 6.2. Starting Node of a Loose Segment Any node along the explicit path that evaluates a loose subobject may initiate the loose segment optimization if all the conditions in section 5 hold. The optimization can be done in the following steps: 1) The RSVP module can query the local registry to obtain information regarding the matching soft FA. If LDP LSPs are used as soft FAs, the query would return the matching LDP LSP. If GRE or IP-in-IP tunnels are used as soft FAs, the query would return the matching GRE or IP-in-IP tunnels. The tunnels could be pre-established or could be established on demand. 2) Standard RSVP mechanisms for handling tunnels should be used to handle signaling over soft FAs. The PATH messages are tunneled directly to the ending node of the loose segment through matching matching soft FA. The PATH message MUST have the Router Alert option so that it can be processed by the egress node of the soft FA. The PATH message should include RSVP HOP object. Since soft FAs may not have logical interfaces associated with them, the previous hop address in the RSVP HOP object should be set to any reachable interface address(router-Id or loopback interface addresses are preferred). The Logical Interface Handle may be zero or may identify the soft FA. 3) The action associated with the locally allocated RSVP label should be swap and the resulting data packets need to be tunneled directly to the egress of the soft FA. If LDP LSPs are used as soft FAs, the label operation for the RSVP LSP should be swap and push to form a label stack with RSVP label as the inner label and LDP label as the outer label. Tian & Shen [Page 4] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 If GRE or IP-in-IP tunnels are used as soft FAs, the RSVP labeled packets will be encapsulated in GRE or IP-in-IP header and tunneled directly to the ending node of the loose segment. If any of the conditions listed above in section 5 fails to hold, then the optimization should not be activated and the RSVP PATH message should be forwarded downstream hop by hop as usual. 6.3. Ending Node of a Loose Segment For the ending node of a loose segment, PATH messages may arrive on a soft FA. In this case, it should send the RESV message directly to the RSVP HOP which may be multiple hops away. Traffic for the RSVP LSP may arrive on an soft FA. The RSVP labeled packet should be processed as normal. If LDP LSPs are used as soft FAs, the outer LDP label will be popped (may be popped on the penultimate hop) and the inner RSVP label will be processed accordingly. If GRE or IP-in-IP tunnels are used as soft FAs, the packets will be decapsulated and then forwarded based on the RSVP label. The ending node of a loose segment may be the starting node of another loose segment, where the same optimization process can repeat again. 6.4. Tail End Node of the RSVP LSP The tail end node of the RSVP LSP may support PHP and advertise implicate null label to the RSVP HOP. In this case traffic on the last loose segment may not contain any RSVP label. If LDP LSPs are used as soft FAs, then over the last loose segment, packets only contain the LDP label. Effectively the RSVP LSP merges into the LDP LSP. 6.5. Minimum Tunnel Span Each node should impose a minimum tunnel span requirement on the soft FAs to avoid using one hop soft FAs for the optimization. If LDP LSPs are used as soft FAs, then the ingress of the LSP may tell whether it is a one hop LSP by looking at the outgoing label. Tian & Shen [Page 5] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 One hop LSPs have either implicit null or explicit null label as outgoing labels. Also the LDP ADDRESS message will list all interface addresses that belong to a given neighbor. If the LSP egress matches any of those addresses, then the LSP is a one hop LSP. If GRE or IP-in-IP tunnels are used as soft FAs, the tunnel length can be derived from the Traffic Engineering Database. Also tools such as traceroute can be used to determine the tunnel length. 7. Loose Segment Optimization in P2MP Traffic Engineering The same optimization can also apply to P2MP traffic engineering, if the point to multi-point LSPs do not have QoS requirements [P2MP- LSP1] [P2MP-LSP2]. The PATH messages for P2MP LSP setup can be tunneled to the next set of branching points through soft FAs, and RESV messages can be sent back to the node where the branches join. Data packets can be replicated at the branching points, then tunneled to the next set of branching points through soft FAs. 8. Security Considerations This document does not introduce any new security issues. 9. IANA Considerations TBD 10. Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of Tian & Shen [Page 6] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 11. References [RSVPTE] Awduche, et al., "Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [LDP] L. Andersson, P. Doolan, N. Feldman, A. Fredette, and B. Thomas, "LDP Specification", RFC 3036, January 2001. [HIER-LSP] K. Kompella, Y. Rekhter, "LSP Hierarchy with Generalized MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, March 2002, work in progress. [P2MP-LSP1] R. Aggarwal, et al., "Establishing Point to Multipoint MPLS TE LSPs", draft-raggarwa-mpls-p2mp-te-01.txt, Work In Progress. [P2MP-LSP2] S. Yasukawa, et al., "Extended RSVP-TE for Point-to-Multipoint LSP Tunnels", draft-yasukawa-mpls-rsvp-p2mp-04.txt, Work In Progress. Tian & Shen [Page 7] Internet Draft draft-tian-rsvp-loose-seg-opt-00.txt July 2004 12. Author Information Albert Jining Tian Redback Networks, Inc. 300 Holger Way San Jose, CA 95134 Email: tian@redback.com Naiming Shen Redback Networks, Inc. 300 Holger Way San Jose, CA 95134 Email: naiming@redback.com Tian & Shen [Page 8]