Network Working Group Praveen Muley Internet Draft Mustapha Aissaoui Expires: March 2007 Matthew Bocci Alcatel Jonathan Newton Cable & Wireless September 22, 2006 Pseudowire (PW) Redundancy draft-muley-pwe3-redundancy-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document may only be posted in an Internet-Draft. 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 This Internet-Draft will expire on March 22, 2007. Abstract This document describes a few scenarios where PW redundancy is needed. A set of redundant PWs is configured between PE nodes in SS- PW applications, or between T-PE nodes in MS-PW applications. In order for the PE/T-PE nodes to indicate the preferred PW path to forward to one another, a new status bit is needed to indicate the Muley et al. Expires March 22, 2007 [Page 1] Internet-Draft Pseudowire (PW) Redundancy) September 2006 preferential forwarding status of active or standby for each PW in the redundancy set. This draft specifies a new PW status bit for this purpose. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1]. Table of Contents 1. Terminology.................................................2 2. Introduction................................................3 3. Multi-homing Single SS-PW redundancy applications............4 3.1. One Multi-homed CE with Single SS-PW redundancy..........4 3.2. Multiple Multi-homed CEs with single SS-PW redundancy....5 4. Multi-homing MS-PW redundancy applications...................6 4.1. Multi-homed CE with MS-PW redundancy....................6 4.2. Single Homed CE with MS-PW redundancy...................7 5. Design considerations........................................8 6. Security Considerations......................................9 7. IANA Considerations.........................................9 7.1. Status Code for PW Preferential Forwarding Status........9 8. Acknowledgments.............................................9 9. References..................................................9 Author's Addresses............................................10 Intellectual Property Statement................................10 Disclaimer of Validity........................................11 Copyright Statement...........................................11 Acknowledgment................................................11 1. Terminology o PW Terminating Provider Edge (T-PE). A PE where the customer- facing attachment circuits (ACs) are bound to a PW forwarder. A Terminating PE is present in the first and last segments of a MS- PW. This incorporates the functionality of a PE as defined in RFC3985 [4]. o Single-Segment Pseudo Wire (SS-PW). A PW setup directly between two T-PE devices. Each PW in one direction of a SS-PW traverses one PSN tunnel that connects the two T-PEs. Muley et al. Expires March 22, 2007 [Page 2] Internet-Draft Pseudowire (PW) Redundancy) September 2006 o Multi-Segment Pseudo Wire (MS-PW). A static or dynamically configured set of two or more contiguous PW segments that behave and function as a single point-to-point PW. Each end of a MS-PW by definition MUST terminate on a T-PE. o PW Segment. A part of a single-segment or multi-segment PW, which is set up between two PE devices, T-PEs and/or S-PEs. o PW Switching Provider Edge (S-PE). A PE capable of switching the control and data planes of the preceding and succeeding PW segments in a MS-PW. The S-PE terminates the PSN tunnels of the preceding and succeeding segments of the MS-PW. o PW switching point for a MS-PW. A PW Switching Point is never the S-PE and the T-PE for the same MS-PW. A PW switching point runs necessary protocols to setup and manage PW segments with other PW switching points and terminating PEs o Active PW. A PW whose preferential status is set to Active and Operational status is UP. o Standby PW. A PW whose preferential status is set to Standby. 2. Introduction In single-segment PW (SS-PW) applications, protection for the PW is provided by the PSN layer. This may be an RSVP LSP with a FRR backup and/or an end-to-end backup LSP. There are however applications where the backup PW terminates on a different target PE node. PSN protection mechanisms cannot protect against failure of the target PE node or the failure of the remote AC. In multi-segment PW (MS-PW) applications, a primary and multiple secondary PWs in standby mode are configured in the network. The paths of these PWs are diverse and are switched at different S-PE nodes. In these applications, PW redundancy is important for the service resilience. This document describes these applications and specifies a new PW status bit to indicate the preferential forwarding status of the PW for the purpose of notifying the remote T-PE of the active/standby state of each PW in the redundancy set. This status bit is different from the operational status bits already defined in the PWE3 control protocol [2]. The PW with both local and remote operational UP status and local and remote preferential active status is selected to forward traffic. Muley et al. Expires March 22, 2007 [Page 3] Internet-Draft Pseudowire (PW) Redundancy) September 2006 3. Multi-homing Single SS-PW redundancy applications 3.1. One Multi-homed CE with single SS-PW redundancy The following figure illustrates an application of single segment pseudo-wire redundancy. |<-------------- Emulated Service ---------------->| | | | |<------- Pseudo Wire ------>| | | | | | | | |<-- PSN Tunnels-->| | | | V V V V | V AC +----+ +----+ AC V +-----+ | | PE1|==================| | | +-----+ | |----------|....|...PW1.(active)...|....|----------| | | | | |==================| | | CE2 | | CE1 | +----+ |PE2 | | | | | +----+ | | +-----+ | | | |==================| | | |----------|....|...PW2.(standby)..| | +-----+ | | PE3|==================| | AC +----+ +----+ Figure 1 Multi-homed CE with single SS-PW redundancy In Figure 1, CE1 is dual homed to PE1 and to PE3 by attachment circuits. The method for dual-homing of CE1 to PE1 and PE3 nodes and the used protocols are outside the scope of this document. PE2 has an attachment circuit from CE2. Two pseudo-wires pw1 and pw2 are established, one connects PE1 to PE2 and the other one connects PE3 to PE2. On PE2, PW1 has a higher priority than PW2 by local configuration. In normal operation, PE1 and PE3 will advertise "Active" and "Standby" preferential forwarding status (apart from operational status) respectively to PE2. This status reflects the forwarding state of the two AC's to CE1. PE2 advertises preferential status of "Active" on both PW1 and PW2. As both the local and remote operational and administrative status for PW1 are UP and Active, traffic is forwarded over PW1 in both directions. On failure of AC to PE1, PE1 sends a PW status notification to PE2 indicating that the AC operational status changed to DOWN. It will also set the forwarding status of PW1 to "standby". PE3 AC will Muley et al. Expires March 22, 2007 [Page 4] Internet-Draft Pseudowire (PW) Redundancy) September 2006 change preferential status to active and this status is also communicated to PE2 using the newly proposed forwarding status bit in the PW status TLV notification message. The changing of preferential status on PE3 due to failure of AC at PE1 is achieved by various methods depending of the used dual-homing protocol and is outside the scope of this draft. On receipt of the status notifications, PE2 switches the path to the standby pseudo-wire PW2 as the newly changed status turns PW2 as Active PW. Note in this example, the receipt of the operational status of the AC on the CE1-PE1 link is normally sufficient to have PE2 switch the path to PW2. However, the operator may want to trigger the switchover of the path of the PW for administrative reasons, i.e., maintenance, and thus the proposed PW forwarding active/standby bit is required to notify PE2 to trigger the switchover. 3.2. Multiple Multi-homed CEs with single SS-PW redundancy |<-------------- Emulated Service ---------------->| | | | |<------- Pseudo Wire ------>| | | | | | | | |<-- PSN Tunnels-->| | | | V V V V | V AC +----+ +----+ AC V +-----+ | |....|.......PW1........|....| | +-----+ | |----------| PE1|...... .........| PE3|----------| | | CE1 | +----+ \ / PW3 +----+ | CE2 | | | +----+ X +----+ | | | | | |....../ \..PW4....| | | | | |----------| PE2| | PE4|--------- | | +-----+ | |....|.....PW2..........|....| | +-----+ AC +----+ +----+ AC Figure 2 Multiple Multi-homed CEs with single SS-PW redundancy In the figure illustrated above the both CEs CE1 and CE2 are dual- homed with PEs, PE1, PE2 and PE3, PE4 respectively. The method for dual-homing and the used protocols are outside the scope of this document. Note that the PSN tunnels are not shown in this figure for clarity. However, it can be assumed that each of the PWs shown is encapsulated in a separate PSN tunnel. PE1 advertises the preferential status "active" and operational status "UP" for pseudo-wires PW1 and PW4 connected to PE3 and PE4. This status reflects the forwarding state of the AC attached to PE1. PE2 advertise preferential status "standby" where as operational Muley et al. Expires March 22, 2007 [Page 5] Internet-Draft Pseudowire (PW) Redundancy) September 2006 status "UP" for pseudo-wires PW2 and PW3 to PE3 and PE4. PE3 advertises preferential status "standby" where as operational status "UP" for pseudo-wires PW1 and PW3 to PE1 and PE2. PE4 advertise the preferential status "active" and operational status "UP" for pseudo- wires PW2 and PW4 to PE2 and PE1 respectively. Thus by matching the local and remote preferential status "active" and operational status "Up" of pseudo-wire the active pseudo-wire is selected. In this case it is the PW4 that will be selected. On failure of AC between the CE1 and PE1 the preferential status on PE2 is changed. Different mechanisms/protocols can be used to achieve this and these are beyond the scope of this document. PE2 then announces the newly changed preferential status "active" to PE3 and PE4. PE1 will advertise a PW status notification message indicating that the AC between CE1 and PE1 is operationally down. PE2 and PE4 checks the local and remote preferential status "active" and operational status "Up" and selects PW2 as the new active pseudo-wire to send traffic. In this application, because each dual-homing algorithm running on the two node sets, i.e., {CE1, PE1, PE2} and {CE2, PE3, PE4}, selects the active AC independently, there is a need to signal the active status of the AC such that the PE nodes can select a common active PW path for end-to-end forwarding between CE1 and CE2. 4. Multi-homing MS-PW redundancy applications 4.1. Multi-homed CE with MS-PW redundancy The following figure illustrates an application of multi-segment pseudo-wire redundancy. Native |<-----------Pseudo Wire----------->| Native Service | | Service (AC) | |<-PSN1-->| |<-PSN2-->| | (AC) | V V V V V V | | +-----+ +-----+ +-----+ +----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+ | |-------|......PW1-Seg1.......|PW1-Seg2.......|-------| | | | | |=========| |=========| | | | | CE1| +-----+ +-----+ +-----+ | | | | |.| +-----+ +-----+ | CE2| | | |.|===========| |=========| | | | | | |.....PW2-Seg1......|.PW2-Seg2......|-------| | +----+ |=============|S-PE2|=========|T-PE4| | +----+ +-----+ +-----+ AC Muley et al. Expires March 22, 2007 [Page 6] Internet-Draft Pseudowire (PW) Redundancy) September 2006 Figure 3 Multi-homed CE with MS-PW redundancy In Figure 3, the PEs that provide PWE3 to CE1 and CE2 are Terminating-PE1 (T-PE1) and Terminating-PE2 (T-PE2) respectively. A PSN tunnel extends from T-PE1 to switching-PE1 (S-PE1) across PSN1, and a second PSN tunnel extends from S-PE1 to T-PE2 across PSN2. PW1 and PW2 are used to connect the attachment circuits (ACs) between T- PE1 and T-PE2. Each PW segment on the tunnel across PSN1 is switched to a PW segment in the tunnel across PSN2 at S-PE1 to complete the multi-segment PW (MS-PW) between T-PE1 and T-PE2. S-PE1 is therefore the PW switching point. PW1 has two segments and is active pseudo- wire while PW2 has two segments and is a standby pseudo-wire. This application requires support for MS-PW with segments of the same type as described in [3]. The operation in this case is the same as in the case of SS-PW. The only difference is that the S-PW nodes need to relay the PW status notification containing both the operational and forwarding status to the T-PE nodes. 4.2. Single Homed CE with MS-PW redundancy This is the main application of interest and the network setup is shown in Figure 3 Native |<------------Pseudo Wire------------>| Native Service | | Service (AC) | |<-PSN1-->| |<-PSN2-->| | (AC) | V V V V V V | | +-----+ +-----+ +-----+ | +----+ | |T-PE1|=========|S-PE1|=========|T-PE2| | +----+ | |-------|......PW1-Seg1.......|.PW1-Seg2......|-------| | | CE1| | |=========| |=========| | | CE2| | | +-----+ +-----+ +-----+ | | +----+ |.||.| |.||.| +----+ |.||.| +-----+ |.||.| |.||.|=========| |========== .||.| |.||...PW2-Seg1......|.PW2-Seg2...||.| |.| ===========|S-PE2|============ |.| |.| +-----+ |.| |.|============+-----+============= .| |.....PW3-Seg1.| | PW3-Seg2......| ==============|S-PE3|=============== | | +-----+ Figure 4 Single homed CE with multi-segment pseudo-wire redundancy Muley et al. Expires March 22, 2007 [Page 7] Internet-Draft Pseudowire (PW) Redundancy) September 2006 In Figure 4, CE1 is connected to PE1 in provider Edge 1 and CE2 to PE2 in provider edge 2 respectively. There are three segmented PWs. A primary PW, PW1, is switched at S-PE1. A standby PW, PW2, which is switched at S-PE2 and has a priority of 1. Finally, another standby PW, PW3, is switched at S-PE3 and has a priority of 2. This means T- PE1 and T-PE2 will select PW1 over PW2, and PW2 over PW3 if all of them are in the UP state. Moreover, a T-PE node will revert back to the primary PW, PW1, whenever it comes back up. The intent of this application is to have T-PE1 and T-PE2 synchronize the transmit and receive paths of the PW over the network. In other words, both T-PE nodes will transmit over the PW segment which is switched by the same S-PE. This is desirable for ease of operation and troubleshooting. Since there is no multi-homing running on the AC, the T-PE nodes would advertise 'Active" for the forwarding status. However, this does not guarantee that the paths of the PW are synchronized because for example of mismatch of the configuration of the PW priority in each T-PE. Thus, there is a need to devise an augmented mechanism to achieve the desirable synchronization of the PW paths and to add the ability to have a T-PE instruct the remote T-PE to perform a coordinated switchover to a common Active path. The solution required for this specific scenario is left for further study. 5. Design considerations While using the pseudo-wire redundancy application, the T-LDP peers MUST negotiate the usage of PW status TLV. The status code defined below carries the active/standby preferential forwarding status of the pseudo-wire. The pseudo-wire is only considered active pseudo- wire only when both the local PW status and the remote PW status indicate preferential status "active" and operational status as Up. Any other status combination keeps the pseudo-wire in standby mode. The pseudo-wires are given different preference level. In case of network failure, the PE/T-PE will first switch to the standby PW with a higher preference. Although the configuration of the pseudo-wire preference is matter of local policy matter and is outside the scope of this, it is desirable to have the preferences configured on both end points be similar. In mis-configuration, a method to force the synchronization of the PW paths is required is for further study. While in standby status, a pseudo-wire can still receive packets in order to avoid black holing of the in-flight packets during switchover. Muley et al. Expires March 22, 2007 [Page 8] Internet-Draft Pseudowire (PW) Redundancy) September 2006 6. Security Considerations This document specifies the LDP extensions that are needed for protecting pseudo-wires. It will have the same security properties as in LDP [5] and the PW control protocol [2]. 7. IANA Considerations We have defined the following codes for the pseudo-wire redundancy application. 7.1. Status Code for PW Preferential Forwarding Status The T-PE nodes need to indicate to each other the preferential forwarding status of active/inactive of the pseudo-wire. 0x00000020 When the bit is set it represents "PW forwarding standby". When the bit is cleared, it represents "PW forwarding "active". 8. Acknowledgments The authors would like to thank Vach Kompella, Kendall Harvey, Tiberiu Grigoriu, Neil Hart, Kajal Saha, and Philippe Niger for their valuable comments and suggestions. 9. References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Martini, L., et al., "Pseudowire Setup and Maintenance using LDP", RFC 4447, April 2006. [3] Martini, L., et al., "Segmented Pseudo Wire", draft-ietf-pwe3- segmented-pw-02.txt, March 2006. [4] Bryant, S., et al., " Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", March 2005 [5] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and B. Thomas, "LDP Specification", RFC 3036, January 2001 Muley et al. Expires March 22, 2007 [Page 9] Internet-Draft Pseudowire (PW) Redundancy) September 2006 Author's Addresses Praveen Muley Alcatel 701 E. Middlefiled Road Mountain View, CA, USA Email: Praveen.muley@alcatel.com Mustapha Aissaoui Alcatel 600 March Rd Kanata, ON, Canada K2K 2E6 Email: mustapha.aissaoui@alcatel.com Matthew Bocci Alcatel Voyager Place, Shoppenhangers Rd Maidenhead, Berks, UK SL6 2PJ Email: matthew.bocci@alcatel.co.uk Jonathan Newton Cable & Wireless Email: Jonathan.Newton@cwmsg.cwplc.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement Muley et al. Expires March 22, 2007 [Page 10] Internet-Draft Pseudowire (PW) Redundancy) September 2006 this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Muley et al. Expires March 22, 2007 [Page 11]