Network Working Group S. Sivabalan Internet-Draft S. Boutros Intended status: Standards Track Cisco Systems, Inc. Expires: May 03, 2016 H. Shah Ciena Corp. S. Aldrin Google Inc. M. Venkatesan Comcast. November 03, 2015 MAC Address Withdrawal over Static Pseudowire draft-ietf-pals-mpls-tp-mac-wd-03.txt Abstract This document specifies a mechanism to signal MAC address withdrawal notification using PW Associated Channel (ACH). Such notification is useful when statically provisioned PWs are deployed in VPLS/H-VPLS environment. Requirements Language 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 [RFC2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on May 3, 2016. Sivabalan, et al. Expires May 03, 2016 [Page 1] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. MAC Withdraw OAM Message . . . . . . . . . . . . . . . . . . 4 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Operation of Sender . . . . . . . . . . . . . . . . . . . 6 4.2. Operation of Receiver . . . . . . . . . . . . . . . . . . 7 5. Security Consideration . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6.1. MPLS G-Ach type . . . . . . . . . . . . . . . . . . . . . 7 6.2. Sequence Number TLV . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 7.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction An LDP-based MAC Address Withdrawal Mechanism is specified in [RFC4762] to remove dynamically learned MAC addresses when the source of those addresses can no longer forward traffic. This is accomplished by sending an LDP Address Withdraw Message with a MAC List TLV containing the MAC addresses to be removed, to all other PEs over the LDP sessions. [RFC7361] describes an optimized MAC withdrawal mechanism which can be used to remove only the set of MAC addresses that need to be re-learned in H-VPLS networks. [RFC7361] also describes optimized MAC Withdrawal operations in PBB-VPLS networks. Sivabalan, et al. Expires May 03, 2016 [Page 2] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 A PW can be signaled via the LDP or can be statically provisioned. In the case of static PW, LDP based MAC withdrawal mechanism cannot be used. This is analogous to the problem and solution described in [RFC6478] where PW OAM message has been introduced to carry PW status TLV using in-band PW Associated Channel. In this document, we propose to use PW OAM message to withdraw MAC address(es) learned via static PW. Thus, MAC withdraw signaling for static PW re-uses concepts of - in-band signaling mechanisms used by static PW status signaling and - MAC withdrawal mechanisms described by [RFC4762] and [RFC7361] The MAC withdraw signaling is a best effort scheme. It is an attempt to optimize the network convergence by reducing blackholes caused by PW failover for protected PWs. The protocol defined in this document addresses possible loss of MAC withdraw signal due to network congestion, but do not assure the guarenteed delivery, as is the case for the LDP based MAC withdraw signaling. In the event that MAC withdraw signaling does not reach the intended target, the fallback to MAC re-learning due to bi-directional traffic or as a last resort to user configured MAC entries age out, will resume the traffic via new PW path. Such fallbacks would cause temporary blackout but does not render network permanently unusable. 2. Terminology The following terminologies are used in this document: ACK: Acknowledgement for MAC withdraw message. LDP: Label Distribution Protocol. MAC: Media Access Control. PE: Provide Edge Node. MPLS: Multi Protocol Label Switching. PW: PseudoWire. PW OAM: PW Operations, Administration and Maintenance. TLV: Type, Length, and Value. VPLS: Virtual Private LAN Services. Sivabalan, et al. Expires May 03, 2016 [Page 3] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 3. MAC Withdraw OAM Message LDP provides a reliable packet transport for control plackets for dynamic PWs. This can be contrasted with static PWs which rely on re-transmission and acknowledgments (ACK) for reliable OAM packet delivery as described in [RFC6478]. The proposed solution for MAC withdrawal over static PW also relies on re-transmissions and ACKs. However, ACK is mandatory. A given MAC withdrawal notification is sent as a PW OAM message, and the sender re-transmits the message for a configured number of times in the absence of an ACK response for the sequence numbered message. The receiver removes the MAC address(es) for a given sequence number MAC withdraw signaling and sends the ACK response. The receipt of same or lower sequence number message is responded with ACK but does not cause removal of MAC addresses. A new TLV to carry the sequence number has been defined. The format of the MAC address withdraw OAM message is shown in Figure 1. The MAC withdraw PW OAM message follows same guidelines used in [RFC6478], whereby first 4-bytes of OAM message header is followed by message specific field and a set of TLVs relevant for the message. Since the MAC withdrawal PW OAM message is not refreshed forever, a MAC address withdraw OAM message MUST contain a "Sequence Number TLV" otherwise the entire message is dropped. It MAY contain MAC Flush Parameter TLVs defined in [RFC7361] when static PWs are deployed in H-VPLS and PBB-VPLS scenarios. The first 2 bits of the sequence number TLV are reserved and MUST be set to 0 on transmit and ignored on receipt. Sivabalan, et al. Expires May 03, 2016 [Page 4] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1|Version| Reserved |(TBD) MAC Withdraw OAM Message | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | TLV Length |A|R| Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Res| Sequence Number TLV (TBD) | Sequence Number TLV Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MAC List TLV | ~ MAC Flush Parameter TLV (optional) ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: MAC Address Withdraw PW OAM Packet Format In this section, MAC List TLV and MAC Flush Parameter TLV are collectively referred to as "MAC TLV(s)". The definition and processing rules of MAC List TLV are described by [RFC4762], and the corresponding rules of MAC Flush Parameter TLV are governed by [RFC7361]. "TLV Length" is the total length of all TLVs in the message, and "Sequence Number TLV Length" is the length of the sequence number field. A single bit (called A-bit) is set by a receiver to acknowledge receipt and processing of a MAC Address Withdraw OAM message. In the acknowledge message, with A-bit set, MAC TLV(s) is/are excluded. A single bit (called R-bit) is set to indicate if the sender is requesting reset of the sequence numbers. The sender sets this bit when the Pseudowire is restarted and has no local record of send and expected receive sequence number. The Sequence number TLV MUST be the first TLV in the message. The lack of reliable transport protocol for the in-band OAM necessitates a presence of sequencing and acknowledgement scheme so that the receiver can recognize newer message from retransmitted older messages. The [RFC4385] describes the details of sequence number handling which includes overflow detection for sequence number field of size 16-bits. This document leverages the same scheme with the two exemptions - sequence number field is of size 32-bits - overflow detection is simplified such that sequence number exceed 2,147,483,647 (0x7FFFFFFF) is considered overflow and reset to 1. Sivabalan, et al. Expires May 03, 2016 [Page 5] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 4. Operation This section describes how the initial MAC withdraw OAM messages are sent and retransmitted, as well as how the messages are processed and retransmitted messages are identified. 4.1. Operation of Sender Each PW is associated with a counter to keep track of the sequence number of the transmitted MAC withdrawal messages. Whenever a node sends a new set of MAC TLVs, it increments the transmitted sequence number counter, and include the new sequence number in the message. The transmit sequence number is initialized to 1 at the onset, after the wrap and after the sequence number reset request receipt. Hence the transmit sequence number is set to 2 in the first MAC withdraw message sent after the sequence number is initialized to 1. The sender expects an ACK from the receiver within a time interval which we call "Retransmit Time" which can be either a default (1 second) or configured value. If the ACK does not arrive within the Retransmit Time, the sender retransmits the message with the same sequence number as the original message. The retransmission MUST be ceased when an ACK is received. In order to avaoid continuous retransmissions in the absence of acknowledgements, a method of suppressing retransmission MUST be implemented. A simple and well used approach is to cease retransmission after a small number of transmissions. A one second retransmission with two retries in the absence of an ACK response is RECOMMENDED. However, both the interval and the number of retries are a local matter which present no interworking issues and thus the operator MAY configure different values. Alternatively, an increasing backoff delay with a larger number of retries MAY be implemented to improve scaling issues. Whilst there are no interworking issues with any of these methods, the implementer must be mindful of not introducing network congestion and must take into account of decaying value of delayed MAC withdraw signaling against possible relearning due to bidirectional traffic or MAC age timeout. During the period of retransmission, if a need to send a new MAC withdraw message with updated sequence number arises then retransmission of the older unacknowledged withdraw message MUST be suspended and retransmit time for the new sequence number MUST be initiated. In essence, sender engages in retransmission logic only for the latest send withdraw message for a given PW. In the event that a Pseudowire was deleted and re-added or the router is restarted with configuration, the local node may lose information about the send sequence number of previous incarnation. This becomes problematic for the remote peer as it will continue to ignore the Sivabalan, et al. Expires May 03, 2016 [Page 6] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 received MAC withdraw messages with lower sequence numbers. In such cases, it is desirable to reset the sequence numbers at both ends of the Pseudowire. The 'R' reset bit is set in the first MAC withdraw to notify the remote peer to reset the send and receive sequence numbers. The 'R' bit must be cleared in subsequent MAC withdraw messages after the acknowledgement is received 4.2. Operation of Receiver Each PW is associated with a register to keep track of the expected sequence number of the MAC withdrawal message and is initialized to 1. Whenever a MAC withdrawal message is received, and if the sequence number on the message is greater than the value in the register, the MAC address(es) contained in the MAC TLV(s) is/are removed, and the register is updated with the received sequence number. The receiver sends an ACK whose sequence number is the same as that in the received message. If the sequence number in the received message is smaller than or equal to the value in the register, the MAC TLV(s) is/are not processed. However, an ACK with the received sequence number MUST be sent as a response. The receiver processes the ACK message as an acknowledgement for all the MAC withdraw messages sent up to the sequence number present in the ACK message and terminates retransmission. The handling of the sequence number is described in section 3. A MAC withdraw message with 'R' bit set MUST be processed by resetting the send and receive sequence number first. The rest of MAC withdraw message processing is performed as described above. The acknowledgement is sent with 'R' bit cleared. 5. Security Consideration The security measures described in [RFC4447], [RFC5085], and [RFC6073] are adequate for the proposed mechanism. 6. IANA Considerations 6.1. MPLS G-Ach type This document requests IANA to assign new channel type (requested value 0x0028) from the registry named "MPLS Generalized Associated Channel (G-ACh) Types (including Pseudwire Associated Channel Types)". The description of the new channel type is "MAC Withdraw OAM Message". [TO BE REMOVED: This registration should take place at the following location: http://www.iana.org/assignments/g-ach- parameters/g-ach-parameters.xhtml]. The channel type value of 0x0028 Sivabalan, et al. Expires May 03, 2016 [Page 7] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 is requested as it is used in implementations that are deployed in the field. 6.2. Sequence Number TLV This document requests IANA to assign a new TLV Type (requested value 0x0001) from the existing LDP "TLV Type Name Space" registry. The description for the new TLV Type is "Sequence Number TLV". [Note to IANA TO BE REMOVED BY THE RFC EDITOR: This registration should take place at the following location: http://www.iana.org/assignments/ldp-namespaces/ldp-namespaces.xhtml]. In an earlier revision of this draft, we created a new sub-TLV registry with one entry, a new "Sequence Number TLV" with the value 0x0001. This has been implemented by several vendors. The IESG proposed that rathen than create a new sub-TLV registry, we just allocate a new code point from the existing LDP "TLV Type Name Space" registry. In this registry, the value 0x0001 is available for allocation by standards action, so we request this code point for the new "Sequence Number" TLV type to avoid needing to change the existing implementations. 7. References 7.1. Normative References [RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson, "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over an MPLS PSN", RFC 4385, February 2006. [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006. [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007. [RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, December 2007. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. Sivabalan, et al. Expires May 03, 2016 [Page 8] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 [RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011. [RFC6478] Martini, L., Swallow, G., Heron, G., and M. Bocci, "Pseudowire Status for Static Pseudowires", RFC 6478, May 2012. [RFC7361] Dutta, P., Balus, F., Stokes, O., Calvignac, G., and D. Fedyk, "LDP Extensions for Optimized MAC Address Withdrawal in a Hierarchical Virtual Private LAN Service (H-VPLS)", RFC 7361, September 2014. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References Authors' Addresses Siva Sivabalan Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario K2K 3E8 Canada Email: msiva@cisco.com Sami Boutros Cisco Systems, Inc. 170 West Tasman Dr. San Jose, CA 95134 US Email: sboutros@cisco.com Himanshu Shah Ciena Corp. 3939 North First Street San Jose, CA 95134 US Email: hshah@ciena.com Sivabalan, et al. Expires May 03, 2016 [Page 9] Internet-Draft MAC Withdrawal over Static Pseudowire October 2015 Sam Aldrin Google Inc. Email: aldrin.ietf@gmail.com Mannan Venkatesan Comcast. 1800 Bishop Gate Blvd Mount Laurel, NJ 08075 US Email: mannan_venkatesan@cable.comcast.com Sivabalan, et al. Expires January 3, 2016 [Page 10]