BESS Workgroup J. Rabadan, Ed.
Internet Draft S. Sathappan
K. Nagaraj
Intended status: Standards Track Nokia
W. Lin
Juniper
Expires: October 27, 2019 April 25, 2019
Propagation of ARP/ND Flags in EVPN
draft-ietf-bess-evpn-na-flags-03
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 proposes an OPTIONAL
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
other groups may also distribute working documents as Internet-
Drafts.
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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 . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
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 proposes an OPTIONAL 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 Discovery (ND)
- 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 MAY be
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 will 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 snooping Neighbor Advertisement messages coming
from the CE. Either way, the PE SHOULD send a MAC/IP Advertisement
route including the learned IPv6->MAC pair and MAY 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 SHOULD 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.
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
document.
5. IANA Considerations
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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]
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>.
6.2. Informative References
7. Acknowledgments
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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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