BESS Workgroup J. Rabadan, Ed. Internet Draft K. Nagaraj S. Sathappan Intended status: Informational V. Prabhu Nokia A. Liu Ciena W. Lin Juniper Networks Expires: July 22, 2018 January 18, 2018 AC-Influenced Designated Forwarder Election for EVPN draft-ietf-bess-evpn-ac-df-03 Abstract The Designated Forwarder (DF) in EVPN networks is the PE responsible for sending multicast, broadcast and unknown unicast traffic to a multi-homed CE, on a given Ethernet Tag on a particular Ethernet Segment (ES). The DF is selected based on the list of PEs that advertise the Ethernet Segment Identifier (ESI) to the EVPN network. While PE node or link failures trigger the DF re-election for a given , individual Attachment Circuit (AC) or MAC-VRF failures do not trigger such DF re-election and the traffic may therefore be permanently impacted, even though there is an alternative path. This document improves the DF election algorithm so that the AC status can influence the result of the election and this type of "logical" failures can be protected too. 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), 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 Rabadan et al. Expires July 22, 2018 [Page 1] Internet-Draft AC-based DF election for EVPN January 18, 2018 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 July 22, 2018. Copyright Notice Copyright (c) 2018 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. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3 2. Solution Description . . . . . . . . . . . . . . . . . . . . . 4 2.1. Current DF Election Procedure And AC Failures . . . . . . . 5 2.2. The Attachment Circuit (AC) Influenced DF Election . . . . 6 2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services . 7 3. Solution benefits . . . . . . . . . . . . . . . . . . . . . . . 8 4. Conventions used in this document . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . . 9 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Rabadan et al. Expires July 22, 2018 [Page 2] Internet-Draft AC-based DF election for EVPN January 18, 2018 1. Problem Statement [RFC7432] defines the Designated Forwarder (DF) as the EVPN PE responsible for: o Flooding Broadcast, Unknown unicast and Multicast traffic (BUM), on a given Ethernet Tag on a particular Ethernet Segment (ES), to the CE. This is valid for single-active and all-active EVPN multi-homing. o Sending unicast traffic on a given Ethernet Tag on a particular ES to the CE. This is valid for single-active multi-homing. The default DF election algorithm defined by [RFC7432] is called service-carving and, for a given ES, is based on a (V mod N)= i function that provides a local DF election of a PEi at level. V is the Ethernet Tag associated to the EVI (the numerically lowest Ethernet Tag value in case of multiple Ethernet Tags), whereas N is the number of PEs for which ES routes have been successfully imported. In other words, EVPN's service-carving takes into account only two variables in the DF election for a given ESI: the existence of the PE's IP address on the candidate list and the locally provisioned Ethernet Tags. If the DF for an fails (due to physical link/node failures) an ES route withdrawn will make the Non-DF (NDF) PEs re- elect the DF for that and the service will be recovered. However the current DF election procedure does not provide a protection against "logical" failures or human errors that may occur at service level on the DF, while the list of active PEs for a given ES does not change. These failures may have an impact not only on the local PE where the issue happens, but also on the rest of the PEs of the ES. Some examples of such logical failures are listed below: a) A given individual Attachment Circuit (AC) defined in an ES is accidentally shutdown or even not provisioned yet (hence the Attachment Circuit Status - ACS - is DOWN), while the ES is operationally active (since the ES route is active). b) A given MAC-VRF - with an ES defined - is shutdown or not provisioned yet, while the ES is operationally active (since the ES route is active). In this case, the ACS of all the AC defined in that MAC-VRF is considered to be DOWN. Neither (a) nor (b) will trigger the DF re-election on the remote PEs for a given ES since the ACS is not taken into account in the DF election procedures. While the ACS is used as a DF election tie- Rabadan et al. Expires July 22, 2018 [Page 3] Internet-Draft AC-based DF election for EVPN January 18, 2018 breaker and trigger in [VPLS-MH], there is no procedure defined in [RFC7432] to trigger the DF re-election based on the ACS change on the DF. This document improves the [RFC7432] service-carving procedure so that the ACS may be taken into account as a variable in the DF election, and therefore EVPN can provide protection against logical failures. 2. Solution Description The ACS for a given Ethernet Tag on an ES is implicitly conveyed in the corresponding EVPN A-D per EVI route for that given . This section describes how to use the A-D per EVI routes to improve the DF election algorithm. Figure 1 illustrates an example EVPN network that will be used to describe the proposed solution. EVI-1 is defined in PE-1, PE-2, PE-3 and PE-4. CE12 is a multi-homed CE connected to ESI12 in PE-1 and PE-2. Similarly CE23 is multi-homed to PE-2 and PE-3 using ESI23. Both, CE12 and CE23, are connected to EVI-1 through VLAN-based service interfaces: CE12-VID 1 (VLAN ID 1 on CE12) is associated to AC1 and AC2 in EVI-1, whereas CE23-VID 1 is associated to AC3 and AC4 in EVI-1. Note that there are other ACs defined on these ES mapped to different EVIs. Rabadan et al. Expires July 22, 2018 [Page 4] Internet-Draft AC-based DF election for EVPN January 18, 2018 +---+ |CE4| +---+ | PE-4 | +-----+-----+ +---------------| +-----+ |---------------+ | | |EVI-1| | | | +-----------+ | | | | EVPN | | | | PE-1 PE-2 PE-3 | | (NDF) (DF) (NDF)| +-----------+ +-----------+ +-----------+ | |EVI-1| | | |EVI-1| | | |EVI-1| | | +-----+ |-------| +-----+ |-------| +-----+ | +-----------+ +-----------+ +-----------+ AC1\ ESI12 /AC2 AC3\ ESI23 /AC4 \ / \ / \ / \ / +----+ +----+ |CE12| |CE23| +----+ +----+ Figure 1 EVPN network example 2.1. Current DF Election Procedure And AC Failures After running the service-carving DF election algorithm, PE-2 turns out to be the DF for ESI12 and ESI23 in EVI-1. The following two examples illustrate the issues with the existing defined procedure in [RFC7432]: a) If AC2 is accidentally shutdown or even not configured, CE12 traffic will be impacted. In case of all-active multi-homing, the BUM traffic to CE12 will be "black-holed", whereas for single-active multi-homing all the traffic to/from CE12 will be discarded. This is due to the fact that a logical failure in PE-2 AC2 may not trigger an ES route withdrawn for ESI12 (since there are still other ACs active on ESI12) and therefore PE-1 will not re-run the DF election procedures. b) If EVI-1 is administratively shutdown or even not configured yet on PE-2, CE12 and CE23 will both be impacted: BUM traffic to both CEs will be discarded in case of all-active multi-homing and all traffic will be discarded to/from the CEs in case of single-active multi-homing. This is due to the fact that PE-1 and PE-3 will not Rabadan et al. Expires July 22, 2018 [Page 5] Internet-Draft AC-based DF election for EVPN January 18, 2018 re-run the DF election procedures and will keep assuming PE-2 is the DF. According to [RFC7432], "when an Ethernet tag is decommissioned on an Ethernet segment, then the PE MUST withdraw the Ethernet A-D per EVI route(s) announced for the that are impacted by the decommissioning", however, while this A-D per EVI route withdrawal is used at the remote PEs performing aliasing or backup procedures, it is not used to influence the DF election for the affected EVIs. 2.2. The Attachment Circuit (AC) Influenced DF Election Modifying the service-carving DF election procedure in the following way solves the issue: 1. When PE-1 and PE-2 discover ESI12, they advertise an ES route for ESI12 with the associated ES-import extended community, starting a timer at the same time. Likewise, PE-2 and PE-3 advertise an ES route for ESI23 and start a timer. 2. Similarly, PE-1 and PE-2 advertise an Ethernet A-D per ES route for ESI12, and PE-2/PE-3 advertise an Ethernet A-D per ES route for ESI23. 3. In addition, PE-1/PE-2/PE-3 advertise an Ethernet A-D per EVI route for AC1, AC2, AC3 and AC4 as soon as the ACs are enabled. Note that the AC can be associated to a single customer VID (e.g. VLAN-based service interfaces) or a bundle of customer VIDs (e.g. VLAN-bundle service interfaces). 4. When the timer expires, each PE builds an ordered "candidate" list of the IP addresses of all the PE nodes connected to the Ethernet Segment (including itself), in increasing numeric order. The candidate list is based on the Originator Router's IP addresses of the ES routes, excluding all the PEs for which no Ethernet A-D per ES route has been received. 5. When electing the DF for a given EVI, a PE will not be considered candidate until an Ethernet A-D per EVI route has been received from that PE. In other words, the ACS on the ESI for a given PE must be UP so that the PE is considered as candidate for a given EVI. For example, PE-1 will not consider PE-2 as candidate for DF election for until an Ethernet A-D per EVI route is received from PE-2 for . 6. Once the PEs with ACS = DOWN for a given EVI have been eliminated Rabadan et al. Expires July 22, 2018 [Page 6] Internet-Draft AC-based DF election for EVPN January 18, 2018 from the candidate list, the (V mod N) = i function can be applied for the remaining N candidates, as per [RFC7432]. Note that this procedure does not modify the existing EVPN control plane whatsoever. It only modifies the candidate list of PEs taken into account for the DF election algorithm defined in [RFC7432]. In addition to the procedure described above, the following events SHALL modify the candidate PE list and trigger the DF re-election in a PE for a given : a) Local ES going DOWN due to a physical failure or reception of an ES route withdraw for that ESI. b) Local ES going UP due to its detection/configuration or reception of a new ES route update for that ESI. c) Local AC going DOWN/UP. d) Reception of a new Ethernet A-D per EVI update/withdraw for the . e) Reception of a new Ethernet A-D per ES update/withdraw for the ESI. This procedure is backwards compatible with the DF election procedures described in [RFC7432] since it does not add any new extension in the control plane, however, a PE not supporting the procedures in this document SHOULD NOT share a multi-homed ES with a PE following this solution since both PEs may end up with an inconsistent view on who the DF is. The AC influenced DF election procedures SHOULD be enabled by an administrative option and only used when all the PEs in the ES support it. The procedure discussed in this section is applicable to the DF Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire Services [RFC8214]. 2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services The procedure described section 2.2 works for VLAN-based and VLAN- bundle service interfaces since, for those service types, a PE advertises only one Ethernet A-D per EVI route per . The withdrawal of such route means that the PE cannot forward traffic on that particular . In VLAN-aware bundle services, the PE advertises multiple Ethernet A- Rabadan et al. Expires July 22, 2018 [Page 7] Internet-Draft AC-based DF election for EVPN January 18, 2018 D per EVI routes per (one route per Ethernet Tag). The withdrawal of an individual route only indicates the unavailability of a specific AC but not necessarily all the ACs in the . For the specific case of VLAN-aware bundle services, the DF election will be influenced by the update/withdraw of any of the Ethernet A-D per EVI routes in the . For example, assuming three bridge tables in PE-1 for the same MAC- VRF (each one associated to a different Ethernet Tag), PE-1 will advertise three Ethernet A-D per EVI routes for . Each of the three routes will indicate the status of each AC in . PE-1 will be considered as a valid candidate PE for DF election as long as the three routes are active. If PE-1 withdraws one or more of the Ethernet A-D per EVI routes for , the PEs in ESI12 will not consider PE-1 as a suitable DF candidate for . 3. Solution benefits The solution described in this document provides the following benefits: a) Improves the DF election procedures for EVPN so that failures due to human errors, logical failures or even delay in provisioning of Attachment Circuits can be protected by multi-homing. b) It does not modify or add any BGP new attributes or NLRI changes. c) It is backwards compatible with the procedures defined in RFC7432. 4. 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 [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying RFC-2119 significance. In this document, the characters ">>" preceding an indented line(s) indicates a compliance requirement statement using the key words listed above. This convention aids reviewers in quickly identifying or finding the explicit compliance requirements of this RFC. Rabadan et al. Expires July 22, 2018 [Page 8] Internet-Draft AC-based DF election for EVPN January 18, 2018 5. Security Considerations The same Security Considerations described in [RFC7432] are valid for this document. 6. IANA Considerations There are no new IANA considerations in this document. 7. References 7.1. Normative References [RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A., Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015, . [RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., Rabadan, J., "Virtual Private Wire Service Support in Ethernet VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017, . 7.2. Informative References [VPLS-MH] Kothari, Henderickx et al., "BGP based Multi-homing in Virtual Private LAN Service", draft-ietf-bess-vpls-multihoming- 01.txt, work in progress, January, 2016. 8. Acknowledgments The authors want to thank Sriram Venkateswaran, Laxmi Padakanti, Ranganathan Boovaraghavan and Ali Sajassi for their review and contributions. 9. Contributors In addition to the authors listed on the front page, the following coauthors have also contributed to this document: Wim Henderickx Nokia Email: wim.henderickx@nokia.com Rabadan et al. Expires July 22, 2018 [Page 9] Internet-Draft AC-based DF election for EVPN January 18, 2018 Patrice Brissette Cisco Systems Email: pbrisset@cisco.com Authors' Addresses Jorge Rabadan Nokia 777 E. Middlefield Road Mountain View, CA 94043 USA Email: jorge.rabadan@nokia.com Kiran Nagaraj Nokia Email: kiran.nagaraj@nokia.com Senthil Sathappan Nokia Email: senthil.sathappan@nokia.com Vinod Prabhu Nokia Email: vinod.prabhu@nokia.com Autumn Liu Ciena Email: hliu@ciena.com Wen Lin Juniper Networks, Inc. Email: wlin@juniper.net Rabadan et al. Expires July 22, 2018 [Page 10]