Propagation of ARP/ND Flags in EVPN
draft-ietf-bess-evpn-na-flags-04

BESS Workgroup                                           J. Rabadan, Ed.
Internet Draft                                              S. Sathappan
                                                              K. Nagaraj
Intended status: Standards Track                                   Nokia

                                                                  W. Lin
                                                                 Juniper

Expires: January 4, 2020                                    July 3, 2019

                  Propagation of ARP/ND Flags in EVPN
                    draft-ietf-bess-evpn-na-flags-04

Abstract

   An EVPN MAC/IP Advertisement route can optionally carry an IPv4 or
   IPv6 addresses associated with a MAC address. Remote PEs can use this
   information to reply locally (act as proxy) to IPv4 ARP requests and
   IPv6 Neighbor Solicitation messages and reduce/suppress the flooding
   produced by the Address Resolution procedure. The information
   conveyed in the MAC/IP 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 host, a router or a host with an anycast
   address, as this information is not carried in the MAC/IP route
   advertisements. Similarly, other information relevant to the IP->MAC
   ARP/ND entries may be needed. 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.

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
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
 

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   and may be updated, replaced, or obsoleted by other documents at any
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   document authors. All rights reserved.

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Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1 Terminology and Conventions  . . . . . . . . . . . . . . . .  3
   2. The EVPN ARP/ND Extended Community  . . . . . . . . . . . . . .  4
   3. Use of the EVPN ARP/ND Extended Community . . . . . . . . . . .  5
   4. Security Considerations . . . . . . . . . . . . . . . . . . . .  6
   5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  7
   6. References  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     6.1. Normative References  . . . . . . . . . . . . . . . . . . .  7
     6.2. Informative References  . . . . . . . . . . . . . . . . . .  8
   7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  8

 

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1. Introduction

   An EVPN MAC/IP Advertisement route can optionally carry an IPv4 or
   IPv6 addresses associated with a MAC address. Remote PEs can use this
   information to reply locally (act as proxy) to IPv4 ARP requests and
   IPv6 Neighbor Solicitation messages and reduce/suppress the flooding
   produced by the Address Resolution procedure. The information
   conveyed in the MAC/IP 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 host, a router or a host with an anycast
   address, as this information is not carried in the MAC/IP route
   advertisements. Similarly, other information relevant to the host
   advertised in the MAC/IP Advertisement route may be needed. 

   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.  

   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].

   IP->MAC: refers to 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.

   Proxy-ARP/ND: refers to a function on the EVPN PEs by which received
 

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   Address Resolution Protocol (ARP) Requests or Neighbor Solicitation
   (NS) messages are replied 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.

   Familiarity with the terminology in [RFC7432] and [RFC4861] is
   expected.

2. The EVPN ARP/ND Extended Community

   This document defines a new EVPN Extended Community with a Type field
   value of 0x06 and a Sub-Type 0x08, as allocated by IANA. 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= TBD |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 octet is defined as the "Router flag". When set,
   the R-bit indicates that the IPv6->MAC pair advertised in the MAC/IP
   Advertisement route along with the extended community belongs to a
   router. If the R-bit 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 is ignored when the extended community is
   advertised with a MAC/IP route for an IPv4->MAC pair.

   O - Override Flag (corresponds to Bit 22 of the extended community)

 

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   Bit 6 of the Flags octet is defined as the "Override flag". An egress
   PE will normally advertise IPv6->MAC pairs with the O-bit set, and
   only when IPv6 "anycast" is enabled in the BD, the PE will send an
   IPv6->MAC pair with the O-bit = 0. The ingress PE will install the ND
   entry with the received O-bit and will use this information when
   replying to a Neighbor Solicitation for the IPv6 address. This flag
   is ignored when the extended community is advertised with a MAC/IP
   route for an IPv4->MAC pair.

   I - Immutable ARP/ND Binding Flag (corresponds to Bit 20 of the
   extended community)

   Bit 4 of the Flags octet is defined as the "Immutable ARP/ND binding
   flag". When set, the egress PE indicates that the IP->MAC pair sent
   in a MAC/IP route along with the extended community is a configured
   ARP/ND entry, and the IP address in the MAC/IP route can only be
   bound together with the MAC address specified in the same route. 

   Bits 0-3 and 5 are not assigned by this document.

3. Use of the EVPN ARP/ND Extended Community

   An EVPN PE supporting a ND/ARP function and implementing the
   propagation of the ARP/ND Flags MUST follow this procedure:

   a) Transmission of the EVPN ARP/ND Extended Community

   A PE may learn the IPv6->MAC pair and its associated ND Flags in the
   management plane or by snooping Neighbor Advertisement messages
   coming from the CE. Either way, the PE sends a MAC/IP Advertisement
   route including the learned IPv6->MAC pair and MUST send the ARP/ND
   Extended Community carrying its associated "R" and "O" Flags. 

   If an IPv4->MAC or IPv6->MAC pair has been learned in the management
   plane (it has been configured) the corresponding MAC/IP Advertisement
   route SHOULD be sent along with an ARP/ND extended community with the
   flag I set.

   This Extended Community does not have any impact on the rest of the
   procedures described in [RFC7432], including the advertisement of the
   MAC Mobility Extended Community along with the MAC/IP Advertisement
   route.

   b) Reception of the EVPN ARP/ND Extended Community

   In addition to the procedures specified in [RFC7432] a PE receiving a
   MAC/IP Advertisement route containing an IPv6 address and the ND
 

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   Extended Community MUST add the R and O Flags to the ND entry for the
   IPv6->MAC entry and use that information in Neighbor Advertisements
   when replying to a Solicitation for the IPv6 address. 

   A PE that implements a proxy-ND function SHOULD have an
   administrative option to define the default Flag to be used in case
   no EVPN ND Extended Community is received for a given IPv6->MAC
   entry. A PE MUST ignore the received R and O Flags for a MAC/IP route
   that contains an IPv4 address.

   A PE receiving a MAC/IP Advertisement route containing an IPv4 or
   IPv6 address and the I flag set, SHOULD install the IP->MAC entry in
   the ARP/ND table as "Immutable binding" entry.

   In a situation where a host (with a IP->MAC configured as Immutable
   binding) 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
   dictate the reachability of the MAC. Receiving multiple MAC/IP routes
   with I=1 for the same IP but different MAC is considered a
   misconfiguration.

   For example, consider PE1, PE2 and PE3 are attached to the same BD.
   PE1 originates a MAC/IP route for IP1->MAC1 with I=1; later on, PE2
   also originates a MAC/IP 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 a MAC/IP route
   for IP1->MAC2 (even with a higher sequence number), then the EVPN PEs
   in the BD SHOULD 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. 

   A PE originating a MAC/IP 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. Also, note that the use of
   the flag I=1 assumes that a given IP is always bound to the same MAC
   address, and therefore some of the mobility procedures described in
   [EXT-MOBILITY] will not apply.

   The flags SHOULD be ignored if they are advertised along with a
   MAC/IP Advertisement route that does not contain an IP address.

4. Security Considerations

   The same security considerations described in [RFC7432] apply to this
 

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   document.

5. IANA Considerations

   This document requests the registration of a new EVPN Extended
   Community sub-type:

   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 octet" where the following allocations are
   made:

   Flag position        Name                            Reference

   0-3          Unassigned
   4            Immutable ARP/ND Binding Flag (I)       [this document]
   5            Unassigned
   6            Override Flag (O)                       [this document]
   7            Router Flag (R)                 [this document]

   The registration procedure for this registry is Standards Action.

6. References

6.1. 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, <https://www.rfc-
   editor.org/info/rfc4861>.

   [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,
   <https://www.rfc-editor.org/info/rfc7432>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
   1997, <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC2119
   Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
   <https://www.rfc-editor.org/info/rfc8174>.
 

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6.2. Informative References

   [EXT-MOBILITY] Malhotra, N. et al., "Extended Mobility Procedures for
   EVPN-IRB", Work in Progress, draft-ietf-bess-evpn-irb-extended-
   mobility-01, June 2019.

7. Acknowledgments

   The authors would like to thank Ali Sajassi for his feedback.

Authors' Addresses

   Jorge Rabadan (Editor)
   Nokia
   777 E. 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

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