BESS Workgroup J. Rabadan, Ed. Internet-Draft S. Sathappan Intended status: Standards Track K. Nagaraj Expires: April 12, 2021 Nokia W. Lin Juniper October 09, 2020 Propagation of ARP/ND Flags in EVPN draft-ietf-bess-evpn-na-flags-07 Abstract This document defines an Extended Community that is advertised along with an EVPN MAC/IP Advertisement route and carries information relevant to the ARP/ND resolution, so that an EVPN PE implementing a proxy-ARP/ND or ARP/ND (on IRB interfaces) function can reply to ARP Requests or Neighbor Solicitations with the correct information. 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 https://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 April 12, 2021. Copyright Notice Copyright (c) 2020 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 (https://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 Rabadan, et al. Expires April 12, 2021 [Page 1] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 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 1.1. Terminology and Conventions . . . . . . . . . . . . . . . 3 2. The EVPN ARP/ND Extended Community . . . . . . . . . . . . . 3 3. Use of the EVPN ARP/ND Extended Community . . . . . . . . . . 5 3.1. Transmission of the EVPN ARP/ND Extended Community . . . 5 3.2. Reception of the EVPN ARP/ND Extended Community . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction An Ethernet Virtual Private Network (EVPN) MAC/IP Advertisement route can optionally carry IPv4 or IPv6 addresses associated with a MAC address. Remote Provider Edge (PE) routers can use this information to populate their Address Resolution Protocol (ARP) or Neighbor Discovery (ND) tables on Integrated Routing and Bridging (IRB) interfaces or their proxy-ARP/ND tables in Broadcast Domains (BD). PEs can then reply locally (act as an ARP/ND proxy, as per [RFC7432]) to IPv4 ARP requests and IPv6 Neighbor Solicitation messages and reduce/suppress the flooding produced by the Address Resolution procedure. However, the information conveyed in the EVPN MAC/IP Advertisement route may not be enough for the remote PE to reply to local ARP or ND requests. For example, if a PE learns an IPv6->MAC ND entry via EVPN, the PE would not know if that particular IPv6->MAC pair belongs to a router or a host, and if that address is an anycast address, as this information is not carried in the EVPN MAC/IP Advertisement routes. This document defines an Extended Community that is advertised along with an EVPN MAC/IP Advertisement route and carries information relevant to the ARP/ND resolution, so that an EVPN PE implementing a proxy-ARP/ND function can reply to ARP Requests or Neighbor Solicitations with the correct information. In particular, the Flags defined in [RFC4861] can now be conveyed along with a MAC/IP Advertisement route, so that an egress EVPN PE can issue Neighbor Advertisement messages with the correct Flag information. Rabadan, et al. Expires April 12, 2021 [Page 2] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 The Flags are carried in the EVPN Address Resolution Protocol (ARP) and Neighbor Discovery (ND) Extended Community, as described in the following sections. 1.1. Terminology and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. EVPN: Ethernet Virtual Private Networks, as in [RFC7432]. BD: Broadcast Domain, also described in [RFC7432]. ARP: Address Resolution Protocol. ND: Neighbor Discovery protocol, specified in [RFC4861]. PE: Provider Edge router. CE: Customer Edge router. IRB: Integrated Routing and Bridging interface. Proxy-ARP/ND: function on the EVPN PEs by which received Address Resolution Protocol (ARP) Requests or Neighbor Solicitation (NS) messages are replied to locally by the PE, without the need to flood the requests to remote PEs in the BD. In order to reply to ARP Requests or NS messages, the PE does a lookup on an ARP/ND table, that is a collection of IP->MAC entries learned by the PE. IP->MAC: an IP address and MAC address combination that represents a given host and is added to an Address Resolution Protocol table or Neighbor Discovery table. This document uses IP->MAC generically for IPv4 and IPv6 addresses. When something is specific to IPv4, the document will use IPv4->MAC and likewise, IPv6->MAC will be used when something is specific to IPv6 entries only. Familiarity with the terminology in [RFC7432] and [RFC4861] is expected. 2. The EVPN ARP/ND Extended Community This document defines a transitive EVPN Extended Community (Type field value of 0x06) with a Sub-Type of 0x08, as allocated by IANA. Rabadan, et al. Expires April 12, 2021 [Page 3] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 It is advertised along with EVPN MAC/IP Advertisement routes that carry an IPv4 or IPv6 address. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=0x06 | Sub-Type=0x08 |Flags (1 octet)| Reserved=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags field: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | |I| |O|R| +-+-+-+-+-+-+-+-+ The following Flags are defined in the Flags field, third octet of the Extended Community: R - Router Flag (corresponds to Bit 23 of the Extended Community) Bit 7 of the Flags field is defined as the "Router Flag". When set, the R Flag indicates that the IPv6->MAC pair advertised in the MAC/IP Advertisement route along with the Extended Community belongs to an IPv6 router. If the R Flag is zero, the IPv6->MAC pair belongs to a host. The receiving PE implementing the ND function will use this information in Neighbor Advertisement messages for the associated IPv6 address. This Flag has no meaning for ARP IPv4->MAC entries and MUST be ignored when the Extended Community is received with an EVPN MAC/IP Advertisement route for an IPv4->MAC pair. O - Override Flag (corresponds to Bit 22 of the Extended Community) Bit 6 of the Flags field is defined as the "Override Flag". An egress PE will normally advertise IPv6->MAC pairs with the O Flag set, and only when IPv6 "anycast" is enabled in the BD or interface, the PE will send an IPv6->MAC pair with the O Flag = 0. The ingress PE will install the ND entry with the received O Flag and will always use this O Flag value when replying to a Neighbor Solicitation for the IPv6 address. Similarly to the Router Flag, the Override Flag has no meaning for ARP IPv4->MAC entries and MUST be ignored when the Extended Community is received with an EVPN MAC/IP Advertisement route for an IPv4->MAC pair. I - Immutable ARP/ND Binding Flag (corresponds to Bit 20 of the Extended Community) Rabadan, et al. Expires April 12, 2021 [Page 4] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 Bit 4 of the Flags field is defined as the "Immutable ARP/ND Binding Flag". When set, the egress PE indicates that the IP->MAC pair sent in an EVPN MAC/IP Advertisement route (along with the Extended Community) is a configured ARP/ND entry. In this case, the IP address in the EVPN MAC/IP Advertisement route can only be bound together with the MAC address specified in the same route, and not with any other MAC addresses received in a different route without the I Flag set. Bits 0-3 and 5 are not assigned by this document. They MUST be set to zero, and ignored on receipt. The reserved fields are set to 0 and ignored by the receiver. 3. Use of the EVPN ARP/ND Extended Community This section describes the relevant procedures when advertising and processing the EVPN ARP/ND Extended Community. In all the procedures below a "PE" must be interpreted as a "PE which supports the ND/ARP proxy function (introduced by [RFC7432]) and implements the propagation of the ARP/ND Flags that this document specifies". 3.1. Transmission of the EVPN ARP/ND Extended Community When an IP->MAC entry is not learned via EVPN, a PE may learn IP->MAC pairs in the management plane (this will create static entries in the ARP/ND or proxy-ARP/ND table) or by snooping ARP or Neighbor Advertisement (NA) messages coming from the CE (this will create dynamic entries). Those static and dynamic IP->MAC entries will be advertised in EVPN MAC/IP Advertisement routes that use the EVPN ARP/ ND Extended Community as follows: o Advertised MAC/IP Advertisement routes for IPv6->MAC entries MUST include one (and only one) ARP/ND Extended Community with the R and O Flag values associated with the entry. Those Flag values are either dynamically learned (from NA messages) or configured in case of static entries. o MAC/IP Advertisement routes for IPv4->MAC entries MAY include one ARP/ND Extended Community. If the EVPN ARP/ND Extended Community is advertised along with an EVPN IPv4/MAC Advertisement route, the R and O Flags SHOULD be set to zero. o If an IP->MAC pair is static (it has been configured) the corresponding MAC/IP Advertisement route MUST be sent along with an ARP/ND Extended Community with the I Flag set. Rabadan, et al. Expires April 12, 2021 [Page 5] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 o This Extended Community does not change the procedures described in [RFC7432]. Specifically the procedures for advertising the MAC Mobility Extended Community along with the MAC/IP Advertisement route are not changed. 3.2. Reception of the EVPN ARP/ND Extended Community In addition to the procedures specified in [RFC7432] a PE receiving a MAC/IP Advertisement route will process the EVPN ARP/ND Extended Community as follows: o Only one EVPN ARP/ND Extended Community is expected to be received along with an EVPN MAC/IP Advertisement route. If more than one ARP/ND Extended Community is received, the PE MUST consider only the first one on the list for processing purposes and MUST NOT propagate the rest of the ARP/ND Extended Communities. o The R, O and I Flags MUST be ignored if they are advertised along with an EVPN MAC/IP Advertisement route that does not contain an IP (IPv4 or IPv6) address. Otherwise they are processed as follows. o R and O Flags processing: * If the EVPN MAC/IP Advertisement route contains an IPv6 address and the EVPN ARP/ND Extended Community, the PE MUST add the R and O Flag values to the ND entry in the ND or proxy-ND table, and propagate the value of the R and O flags from the ARP/ND Extended Community to the Neighbor Advertisements when replying to a Solicitation for the IPv6 address. * If no EVPN ARP/ND Extended Community is received along with the route, the PE will add the default R and O Flags to the entry. The default R Flag SHOULD be an administrative choice. The default O Flag SHOULD be 1. * A PE MUST ignore the received R and O Flags for an EVPN MAC/IP Advertisement route that contains an IPv4->MAC pair. o I Flag processing: * A PE receiving an EVPN MAC/IP Advertisement route containing an IP->MAC and the I Flag set SHOULD install the IP->MAC entry in the ARP/ND or proxy-ARP/ND table as an "Immutable binding". This Immutable binding entry will override an existing non- immutable binding for the same IP->MAC. The absence of the EVPN ARP/ND Extended Community in a MAC/IP Advertisement route indicates that the IP->MAC entry is not an "Immutable binding". Rabadan, et al. Expires April 12, 2021 [Page 6] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 * Receiving multiple EVPN MAC/IP Advertisement routes with I=1 for the same IP but different MAC is considered a misconfiguration. Note that if a configured IP1->MAC1 changes to point to a new MAC address, i.e., IP1->MAC2, the EVPN MAC/IP Advertisement route for IP1->MAC1 will be withdrawn before the EVPN MAC/IP Advertisement route for IP1->MAC2 is advertised. * A PE originating an EVPN MAC/IP Advertisement route for IP1->MAC1 with I=1 MAY also originate the route with the Static bit set (in the MAC Mobility Extended Community). In such a case, the IP1->MAC1 binding is not only immutable but it cannot move as well. Even so, if an update for the same IP1->MAC1 immutable and static, is received from a different PE, one of the two routes will be selected, as in the [RFC7432] case where two MAC/IP routes with Static bit are received for the same MAC from different PEs. In a situation where a host (with an IP->MAC that is configured as Immutable binding in the attached PE) is allowed to move between PEs (that is, the associated MAC is non-static), PEs can receive multiple MAC/IP advertisement routes for the same IP->MAC. In such situations, MAC mobility procedures as in [RFC7432] dictate the reachability of the MAC. As an example of the use of the I Flag, consider PE1, PE2 and PE3 are attached to the same BD. PE1 originates an EVPN MAC/IP Advertisement route for IP1->MAC1 with I=1; later on, PE2 also originates an EVPN MAC/IP Advertisement route IP1->MAC1 with a higher sequence number and I=1. Then all the EVPN PEs attached to the same BD SHOULD retain their IP1->MAC1 ARP/ND binding but update MAC1's forwarding destination to PE2. If for some reason, PE3 originates an EVPN MAC/ IP Advertisement route for IP1->MAC2 with I=0 (even with a higher sequence number), then the EVPN PEs in the BD will not update their IP1->MAC1 ARP/ND bindings, since IP1 is bound to MAC1 (MAC2 SHOULD still be programmed in the layer-2 BDs). This is considered a misconfiguration in PE3. The use of the Flag I=1 assumes that a given IP is always bound to the same MAC address, and therefore the mobility procedures described in [I-D.ietf-bess-evpn-irb-extended-mobility] for "Host IP move to a new MAC" will not apply. 4. Security Considerations The same security considerations described in [RFC7432] apply to this document. Rabadan, et al. Expires April 12, 2021 [Page 7] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 In addition, this document adds pieces of information that impact on the way ARP/ND entries are installed in ARP/ND and/or proxy-ARP/ND tables, and therefore the resolution protocols for IPv4 and IPv6 addresses. For instance, if a given IPv6->MAC binding is configured with the wrong R or O Flags (intentionally or not) on a given PE, the rest of the PEs attached to the same BD will install the wrong information for the IPv6->MAC. This will cause all the PEs in the BD to reply to Neighbor Solicitations for the IPv6 with Neighbor Advertisement (NA) messages containing the wrong R and O Flags. For example, as specified in [RFC4861], the receiver of a NA message with O not set will not update its existing cache entry for the IP->MAC, hence the communication between the owner of the IP address and the receiver of the NA message with the wrong O flag will fail. Similarly, the receiver of a NA message with the wrong R flag, may update its Default Router List incorrectly adding or removing an entry, which could for example lead to sending traffic to a node that is not a router, causing the traffic to be dropped . The I Flag, or Immutable ARP/ND Binding Flag, introduces a useful security tool so that an operator makes sure a given IP address is always bound to the same MAC and that information is distributed to all the PEs attached to the same BD. ARP/ND spoofing attacks from hosts injecting Gratuitous ARPs or unsolicited Neighbor Advertisement messages for that IP address with a different MAC address will not succeed to be programmed in ARP/ND and proxy-ARP/ND tables and therefore will avoid attracting traffic to the spoofer. 5. IANA Considerations This document request that the Name of the currently registered value for Sub-Type 0x08 in the EVPN Extended Community Sub-Types registry (https://www.iana.org/assignments/bgp-extended-communities/bgp- extended-communities.xhtml#evpn) be changed to: +----------+---------------------------+-----------------+ | Sub-Type | Name | Reference | +----------+---------------------------+-----------------+ | 0x08 | ARP/ND Extended Community | [this document] | +----------+---------------------------+-----------------+ This document also requests the creation of a registry called "ARP/ND Extended Community Flags" where the following initial allocations are made: Rabadan, et al. Expires April 12, 2021 [Page 8] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 +---------------+---------------------------------+-----------------+ | Flag position | Name | Reference | +---------------+---------------------------------+-----------------+ | 0-3 | Unassigned | - | | 4 | Immutable ARP/ND Binding Flag | [this document] | | | (I) | | | 5 | Unassigned | - | | 6 | Override Flag (O) | [this document] | | 7 | Router Flag (R) | [this document] | +---------------+---------------------------------+-----------------+ The registration procedure for this registry is Standards Action. This registry should be located in the Border Gateway Protocol (BGP) Extended Communities general registry (https://www.iana.org/assignments/bgp-extended-communities/bgp- extended-communities.xhtml). 6. Acknowledgments The authors would like to thank Ali Sajassi for his feedback. 7. References 7.1. Normative References [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Rabadan, et al. Expires April 12, 2021 [Page 9] Internet-Draft EVPN Neighbor Advertisement Flags October 2020 7.2. Informative References [I-D.ietf-bess-evpn-irb-extended-mobility] Malhotra, N., Sajassi, A., Pattekar, A., Lingala, A., Rabadan, J., and J. Drake, "Extended Mobility Procedures for EVPN-IRB", draft-ietf-bess-evpn-irb-extended- mobility-03 (work in progress), May 2020. Authors' Addresses Jorge Rabadan (editor) Nokia 777 Middlefield Road Mountain View, CA 94043 USA Email: jorge.rabadan@nokia.com Senthil Sathappan Nokia 701 E. Middlefield Road Mountain View, CA 94043 USA Email: senthil.sathappan@nokia.com Kiran Nagaraj Nokia 701 E. Middlefield Road Mountain View, CA 94043 USA Email: kiran.nagaraj@nokia.com Wen Lin Juniper Networks Email: wlin@juniper.net Rabadan, et al. Expires April 12, 2021 [Page 10]