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Versions: (draft-yizhou-trill-arp-optimization) 00 01 02 03 04 05 06 07

TRILL Working Group                                                Y. Li
INTERNET-DRAFT                                               D. Eastlake
Intended Status: Standard Track                                L. Dunbar
                                                     Huawei Technologies
                                                              R. Perlman
                                                                M. Umair
Expires: April 24, 2017                                 October 21, 2016

                       TRILL: ARP/ND Optimization


   This document describes mechanisms to optimize the ARP (Address
   Resolution Protocol) and ND (Neighbor Discovery) traffic in TRILL
   campus. Such optimization reduces packet flooding over a TRILL

Status of this Memo

   This Internet-Draft is submitted to IETF 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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   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright and License Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the

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   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 . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2 ARP/ND Optimization Requirement and Solution . . . . . . . . . .  4
   3 IP/MAC Address Mappings  . . . . . . . . . . . . . . . . . . . .  5
   4 Handling ARP/ND Messages . . . . . . . . . . . . . . . . . . . .  5
     4.1 Get Sender's IP/MAC Mapping Information for Non-zero IP  . .  6
     4.2 Determine How to Reply to ARP/ND . . . . . . . . . . . . . .  6
     4.3 Determine How to Handle the ARP/ND Response  . . . . . . . .  8
   5 Handling RARP (Reverse Address Resolution Protocol) Messages . .  8
   6 Handling of DHCP messages  . . . . . . . . . . . . . . . . . . .  9
   7 Handling of Duplicate IP Addresses . . . . . . . . . . . . . . .  9
   8 ARP/ND Cache Liveness and MAC Mobility . . . . . . . . . . . . . 10
   9 Security Considerations  . . . . . . . . . . . . . . . . . . . . 10
   10 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11
   11 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 11
   12 References  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     12.1 Normative References  . . . . . . . . . . . . . . . . . . . 11
     12.2 Informative References  . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1 Introduction

   ARP [RFC826] and ND [RFC4861] are normally sent by broadcast and
   multicast respectively. To reduce the burden on a TRILL campus caused
   by these multi-destination messages, RBridges MAY implement an
   "optimized ARP/ND response", as specified herein, when the target's
   location is known by the ingress RBridge or can be obtained from a
   directory. This avoids ARP/ND query and answer flooding.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

   The acronyms and terminology in [RFC6325] are used herein. Some of
   these are listed below for convenience  along with some additions:

   APPsub-TLV     Application sub-Type-Length-Value [RFC6823]

   ARP            Address Resolution Protocol [RFC826]

   Campus         A TRILL network consisting of RBridges, links, and
   possibly bridges bounded by end stations and IP routers [RFC6325]

   DAD            Duplicate Address Detection

   Data Label     VLAN or FGL

   ESADI          End Station Address Distribution Information [RFC7357]

   FGL            Fine-Grained Label [RFC7172]

   IA             Interface Addresses, a TRILL APPsub-TLV [RFC7961]

   IP             Internet Protocol, both IPv4 and IPv6

   MAC            Media Access Control [RFC7042]

   ND             Neighbor Discovery [RFC4861]

   RBridge        A contraction of "Routing Bridge". A device
   implementing the TRILL protocol.

   SEND           secure neighbor discovery [RFC3971]

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   TRILL          Transparent Interconnection of Lots of Links or
   Tunneled Routing in the Link Layer [RFC6325] [RFC7780]

2 ARP/ND Optimization Requirement and Solution

   IP address resolution can create significant issues in data centers
   due to flooded packets as discussed in [RFC6820]. Such flooding can
   be avoided by a proxy ARP/ND function on edge RBridges as described
   in this document.

   To support such ARP/ND optimization, edge RBridges need to know end-
   station's IP to MAC mapping through manual configuration
   (management), through control plane mechanisms such as directories
   [DirMech], or through Data plane learning by snooping of messages
   such as ARP/ND (including DHCP or gratuitous ARP_messages).

   When all the end-stations IP/MAC address mapping is known to edge
   RBridges or provisioned through management or learnt via control
   plane on the edge RBridges, it should be possible to completely
   suppress flooding of ARP/ND messages in TRILL Campus, When all end-
   station MAC addresses are similarly known, it should be possible to
   suppress unknown unicast by dropping any unknown unicast received at
   an edge RBridge.

   An ARP/ND optimization mechanism should include provisions for an
   edge RBridge to issue an ARP/ND request to an attached end station to
   confirm or update information and should allow an end station to
   detect duplicate IP addresses.

   This solution should provide an option to disable any data-plane
   learning on a per port basis.

   Most of the end station hosts either send DHCP messages requesting an
   IP Address send out gratuitous ARP or RARP requests to announce
   themselves to the network right after they come online. Thus the
   local edge RBridge will immediately have the opportunity to snoop and
   learn their MAC and IP addresses and distribute this information to
   other edge RBridges through the TRILL control plane ESADI [RFC7357]
   protocol. Once remote RBridges received this information via the
   control plane they should add IP to MAC mapping information to their
   ARP/ND cache along with the nickname and data label of the address
   information. Therefore, most active IP hosts in TRILL network can be
   learned by the edge RBridges either through local learning or
   control-plane-based remote learning. As a result, ARP suppression can
   vastly reduce the network flooding caused by host ARP learning

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3 IP/MAC Address Mappings

   By default, an RBridge [RFC6325] [RFC7172] learns MAC Address and
   Data Label (VLAN or FGL) to egress nickname mapping information from
   TRILL data frames it receives. No IP address information is learned
   directly from the TRILL data frame. Interface Addresses (IA) APPsub-
   TLV [RFC7961] enhances the TRILL base protocol by allowing IP and MAC
   address mappings to be distributed in the control plane by any
   RBridge. This APPsub-TLV appears inside the TRILL GENINFO TLV in
   ESADI [RFC7357] but the value data structure it specifies may also
   occur in other application contexts. Edge Directory Assist Mechanisms
   [DirMech] makes use of this APPsub-TLV for its push model and uses
   the value data structure it specifies in its pull model.

   An RBridge can easily know the IP/MAC address mappings of the local
   end stations that it is attached to it via its access ports by
   receiving ARP [RFC826] or ND [RFC4861] messages. If the RBridge has
   extracted the sender's IP/MAC address pair from the received data
   packet (either ARP or ND), it may save the information and then use
   the IA APPsub-TLV (to link the IP and MAC addresses) to distribute it
   to other RBridges through ESADI. Then the relevant remote RBridges
   (normally those interested in the same Data Label as the original
   ARP/ND messages) also receive and save such mapping information.
   There are others ways that RBridges save IP/MAC address mappings in
   advance, e.g. import from management system and distribution by
   directory servers [DirMech].

   The examples given above show that RBridges might have saved an end
   station's triplet of {IP address, MAC address, ingress nickname} for
   a given Data Label (VLAN or FGL) before that end station sends or
   receives any real data packet. Note such information might or might
   not be a complete list and might or might not exist on all RBridges.
   The information could possibly be from different sources. RBridges
   can then use the Flags Field in IA APPsub-TLV to identify if the
   source is a directory server or local observation by the sender. A
   different confidence level may also be used to indicate the
   reliability of the mapping information.

4 Handling ARP/ND Messages

   A native frame that is an ARP [RFC826] message is detected by its
   Ethertype of 0x0806. A native frame that is an ND [RFC4861] is
   detected by being one of five different ICMPv6 packet types. ARP/ND
   is commonly used on a link to (1) query for the MAC address
   corresponding to an IPv4 or IPv6 address, (2) test if an IPv4/IPv6
   address is already in use, or (3) to announce the new or updated info
   on any of IPv4/IPv6 address, MAC address, and/or point of attachment.

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   To simplify the text, we use the following terms in this section.

     1) IP address - indicated protocol address that is normally an IPv4
     address in ARP or an IPv6 address in ND.

     2) sender's IP/MAC address - sender IP/MAC address in ARP, source
     IP address and source link-layer address in ND

     3) target's IP/MAC address - target IP/MAC address in ARP, target
     address and target link-layer address in ND

   When an ingress RBridge receives an ARP/ND message, it can perform
   the steps described in the sub-sections below.

4.1 Get Sender's IP/MAC Mapping Information for Non-zero IP

   o   If the sender's IP is not present in the ingress RBridge's ARP/ND
   cache, populate the information of sender's IP/MAC in its ARP/ND
   cache table. The ingress RBridge correlates its nickname and that
   IP/MAC mapping information. Such triplet of {IP address, MAC address,
   ingress nickname} information is saved locally and can be distributed
   to other RBridges as explain later.

   o   Else if the sender's IP has been saved before but with a
   different MAC address mapped or a different ingress nickname
   associated with the same pair of IP/MAC, the RBridge SHOULD verify if
   a duplicate IP address has already been in use or an end station has
   changed its attaching RBridge. The RBridge may use different
   strategies to do so. For example, the RBridge might ask an
   authoritative entity like directory servers or it might encapsulate
   and unicast the ARP/ND message to the location where it believes the
   address is in use. RBridge SHOULD update the saved triplet of {IP
   address, MAC address, ingress nickname} based on the verification. An
   RBridge might not verify an IP address if the network manager's
   policy is to have the network behave, for each Data Label, as if it
   were a single link and just believe an ARP it receives.

   The ingress RBridge MAY use the IA APPsub-TLV [RFC7961] with the
   Local flag set in ESADI [RFC7357] to distribute any new or updated
   triplet of {IP address, MAC address, ingress nickname} information
   obtained in this step. If a push directory server is used, such
   information can be distributed as per [DirMech].

4.2 Determine How to Reply to ARP/ND

   The options for an edge RBridge to handle a native ARP/ND are given
   below. For generic ARP/ND request seeking the MAC address

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   corresponding to an IP address, if the edge RBridge knows the IP
   address and corresponding MAC, behavior is as in item (a), otherwise
   behavior is as in item (b). Behavior for gratuitous ARP and ND
   Unsolicited Neighbor Advertisements [RFC4861] is given in item (c).
   And item (d) covers handling of Address Probe ARP Query.

   a) If the message is a generic ARP/ND request and the ingress RBridge
   knows the target's IP address and associated MAC address, the ingress
   RBridge MUST take one or a combination of the actions below. In the
   case of secure neighbor discovery (SEND) [RFC3971], cryptography
   would prevent local reply by the ingress RBridge, since the RBridge
   would not be able to sign the response with the target's private key
   and only action a.2 or a.5 is valid.

     a.1. Send an ARP/ND response directly to the querier, using the
     target's MAC address present in the ingress RBridge's ARP/ND cache
     table. Because the edge RBridge might not have an IPv6 address, the
     source IP address for such an ND response MUST be that of the
     target end station.

     a.2. Encapsulate the ARP/ND request to the target's Designated
     RBridge, and have the egress RBridge for the target forward the
     query to the target. This behavior has the advantage that a
     response to the request is authoritative. If the request does not
     reach the target, then the querier does not get a response.

     a.3. Block ARP/ND requests that occur for some time after a request
     to the same target has been launched, and then respond to the
     querier when the response to the recently-launched query to that
     target is received.

     a.4  Reply to the querier based on directory information [DirMech]
     such as information obtained from a pull directory server or
     directory information that the ingress RBridge has requested to be
     pushed to it.

     a.5. Flood the request as per [RFC6325].

   (b) If the message is a generic ARP/ND request and the ingress
   RBridge does not know target's IP address, the ingress RBridge MUST
   take one of the following actions.  In the case of secure neighbor
   discovery (SEND) [RFC3971], cryptography would prevent local reply by
   the ingress RBridge, since the RBridge would not be able to sign the
   response with the target's private key and only action b.1 is valid.

     b.1. Flood the message as per [RFC6325].

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     b.2. Use directory server to pull the information [DirMech] and
     reply to the querier.

     b.3. Drop the message if the directory mechanism is used and you
     know there should be no response (query based on an non-existent IP
     address for example).

   (c) If the message is a gratuitous ARP which can be identified by the
   same sender's and target's "protocol" address fields or an
   Unsolicited Neighbor Advertisements [RFC4861] in ND:

   The RBridge MAY use an IA APPsub-TLV [RFC7961] with the Local flag
   set to distribute the sender's MAC and IP mapping information. When
   one or more directory servers are deployed and complete Push
   Directory information is used by all the RBridges in the Data Label,
   a gratuitous ARP or unsolicited NA SHOULD be discarded rather than
   ingressed. Otherwise, they are either ingressed and flooded as per
   [RFC6325] or discarded depending on local policy.

   (d) If the message is a Address Probe ARP Query [RFC5227] which can
   be identified by the sender's protocol (IPv4) address field being
   zero and the target's protocol address field being the IPv4 address
   to be tested or a Neighbor Solicitation for DAD (Duplicate Address
   Detection) which has the unspecified source address [RFC4862]: it
   SHOULD be handled as the generic ARP message as in (a) or (b) above.

   It is not essential that all RBridges use the same strategy for which
   option to select for a particular ARP/ND query. It is up to the

4.3 Determine How to Handle the ARP/ND Response

   If the ingress RBridge R1 decides to unicast the ARP/ND request to
   the target's egress RBridge R2 as discussed in subsection 3.2 item a)
   or to flood the request as per [RFC6325], then R2 decapsulates the
   query, and initiates an ARP/ND query on the target's link. When/if
   the target responds, R2 encapsulates and unicasts the response to R1,
   which decapsulates the response and sends it to the querier. R2
   SHOULD initiate a link state update to inform all the other RBridges
   of the target's location, layer 3 address, and layer 2 address, in
   addition to forwarding the reply to the querier. The update uses an
   IA APPsub-TLV [IA-draft] (so the layer 3 and layer 2 addresses can be
   linked) with the Local flag set in ESADI [RFC7357] or as per
   [DirMech] if push directory server is in use.

5 Handling RARP (Reverse Address Resolution Protocol) Messages

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   RARP [RFC903] uses the same packet format as ARP but a different
   Ethertype (0x8035) and opcode values. Its use is similar to the
   generic ARP Request/Response as described in 3.2 a) and b).  The
   difference is that it is intended to query for the target "protocol"
   (IP) address corresponding to the target "hardware" (MAC) address
   provided. It SHOULD be handled by doing a local cache or directory
   server lookup on the target "hardware" address provided to find a
   mapping to the desired "protocol" address. Normally, it is used to
   look up a MAC address to find the corresponding IP address.

6 Handling of DHCP messages

   When a newly connected end-station exchanges messages with a DHCP
   [RFC2131] server an edge RBridge should snoop them (mainly the
   DHCPAck message) and store IP/MAC mapping information in its ARP/ND
   cache and should also send the information out through the TRILL
   control plane.

7 Handling of Duplicate IP Addresses

   Duplicate IP addresses within a Data Label can occur due to an
   attacker sending fake ARP/ND messages or due to human/configuration
   errors. If complete directory information is available, then by
   definition the IP location information in the directory is correct.
   Any appearance of an IP address in a different place (different edge
   RBridge or port) from other sources is not correct.

   Without complete directory information, the ARP/ND optimization
   function should support duplicate IP detection. This is critical in a
   Data Center to stop an attacker from using ARP/ND spoofing to divert
   traffic from its intended destination.

   Duplicate IP addresses can be detected when an existing active
   IP1/MAC1 mapping gets modified. Also an edge RBridge may send a query
   to the former owner of IP called a DAD-query (Duplicate Address
   Detection query). A DAD-query is a unicast ARP/ND message with sender
   IP in case of ARP (or a configurable per RBridge IP address
   called the DAD-Query source IP) and an IPv6 Link Local Address in
   case of ND with source MAC set to the DAD-querier RBridge's MAC. If
   the querying RBridge does not receive an answer within a given time,
   the new IP entry will be confirmed and activated in its ARP/ND

   In the case where the former owner replies, a Duplicate Address has
   been detected. In this case the querying RBridge SHOULD log the
   duplicate so that the network administrator can take appropriate

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8 ARP/ND Cache Liveness and MAC Mobility

   A maintenance procedure is needed for ARP/ND caching to ensure IP
   end-stations connected to ingress RBridges are still active.

   Some links provide a physical layer indication of link liveness. A
   dynamic proxy-ARP/ND entry (one learned from data plane observation)
   MUST be removed from the table if the link over which it was learned

   Similarly a dynamic proxy-ARP/ND entry SHOULD be flushed out of the
   table if the IP/MAC mapping has not been refreshed within a given
   age-time. The entry is refreshed if an ARP or ND message is received
   for the same IP/MAC mapping entry from any location. The IP/MAC
   mapping information ageing timer is configurable per RBridge and
   defaults to 3/4 of the MAC address learning Ageing Timer [RFC6325].

   For example end-Station "A" is connected to edge-RBridge1 (RB1) and
   learnt as local entry on RB1. If end-Station "A" moves to some other
   location (MAC/VM Mobility) and gets connected to egde-RBridge2 (RB2),
   after learning on RB2's access port, RB2 advertise this entry through
   the TRILL control-plane and it gets learnt on RB1 as a remote entry.
   The old entry on RB1 SHOULD get replaced and all other edge-RBridges
   with end-station service enabled for that data-label should update
   the entry to show reachability from RB2 instead of RB1.

   If ARP/ND entry in the cache is not refreshed, then the RBridge
   connected to that Host MAY send periodic refresh messages (ARP/ND
   "probes") to the owners of the dynamic Proxy-ARP/ND entries, so that
   the entries can be refreshed before they age out. The owner of the
   IP/MAC mapping entry would reply to the ARP/ND probe and the
   corresponding entry age-timer resets.

9 Security Considerations

   Unless Secure ND (SEND [RFC3971]) is used, ARP and ND messages can be
   easily forged. Therefore the learning of MAC/IP addresses from ARP/ND
   should not be considered as reliable without SEND. RBridge can use
   the confidence level in IA APPsub-TLV information received via ESADI
   or pull directory retrievals to determine the reliability of MAC/IP
   address mapping. ESADI information can be secured as provide in
   [RFC7357] and pull directory information can be secured as provide in
   [DirMech]. The implementation decides if an RBridge will distribute
   the IP and MAC address mappings received from local native ARP/ND
   messages to other RBridges in the same Data Label and with what
   confidence level.

   The ingress RBridge SHOULD also rate limit the ARP/ND queries for the

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   same target to be injected into the TRILL campus to prevent possible
   denial of service attacks.

10 IANA Considerations

   No IANA action is required. RFC Editor: please delete this section
   before publication.

11 Acknowledgments

   The authors would like to thank Igor Gashinsky for his contributions.

12 References

12.1 Normative References

   [RFC826]  Plummer, D., "An Ethernet Address Resolution Protocol", RFC
              826, November 1982.

   [RFC903]  Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
              Reverse Address Resolution Protocol", STD 38, RFC 903,
              June 1984

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, July 2011.

   [RFC7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
              D. Dutt, "Transparent Interconnection of Lots of Links
              (TRILL): Fine-Grained Labeling", RFC 7172, May 2014.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding

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              Scope Link State PDUs (LSPs)", RFC 7356, September 2014.

   [RFC7357]  Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
              Stokes, "Transparent Interconnection of Lots of Links
              (TRILL): End Station Address Distribution Information
              (ESADI) Protocol", RFC 7357, September 2014.

   [RFC7780]  Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
              Ghanwani, A., and S. Gupta, "Transparent Interconnection
              of Lots of Links (TRILL): Clarifications, Corrections, and
              Updates", RFC 7780, February 2016.

   [RFC7961] Eastlake 3rd, D. and L. Yizhou, "Transparent
              Interconnection of Lots of Links (TRILL): Interface
              Addresses APPsub-TLV", RFC 7961, August 2016.

   [DirMech] Dunbar, L., Eastlake 3rd, D., Perlman, R., I. Gashinsky.
              and Li Y., TRILL: Edge Directory Assist Mechanisms",
              draft-ietf-trill-directory-assist-mechanisms, work in

12.2 Informative References

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC5227]  Cheshire, S., "IPv4 Address Conflict Detection", RFC 5227,
              July 2008.

   [RFC6820]  Narten, T., Karir, M., and I. Foo, "Address Resolution
              Problems in Large Data Center Networks", RFC 6820, January

   [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", RFC 6823, December 2012.

   [RFC7042]  Eastlake 3rd, D. and J. Abley, "IANA Considerations and
              IETF Protocol and Documentation Usage for IEEE 802
              Parameters", BCP 141, RFC 7042, October 2013.

Authors' Addresses

   Yizhou Li
   Huawei Technologies
   101 Software Avenue,

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   Nanjing 210012

   Phone: +86-25-56625375
   EMail: liyizhou@huawei.com

   Donald Eastlake
   Huawei R&D USA
   155 Beaver Street
   Milford, MA 01757 USA

   Phone: +1-508-333-2270
   EMail: d3e3e3@gmail.com

   Linda Dunbar
   Huawei Technologies
   5430 Legacy Drive, Suite #175
   Plano, TX 75024, USA

   Phone: +1-469-277-5840
   EMail: ldunbar@huawei.com

   Radia Perlman
   2010 256th Avenue NE, #200
   Bellevue, WA 98007

   EMail: Radia@alum.mit.edu

   Mohammed Umair

   Email: mohammed.umair2@gmail.com

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