Skip to main content

Transparent Interconnection of Lots of Links (TRILL): ARP and Neighbor Discovery (ND) Optimization

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8302.
Authors Yizhou Li , Donald E. Eastlake 3rd , Linda Dunbar , Radia Perlman , Mohammed Umair
Last updated 2018-01-05 (Latest revision 2017-10-08)
Replaces draft-yizhou-trill-arp-optimization, draft-trill-trill-arp-optimization
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Susan Hares
Shepherd write-up Show Last changed 2017-05-31
IESG IESG state RFC 8302 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Alia Atlas
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
RFC Editor RFC Editor state AUTH48-DONE
TRILL Working Group                                                Y. Li
INTERNET-DRAFT                                               D. Eastlake
Intended Status: Standard Track                                L. Dunbar
                                                     Huawei Technologies
                                                              R. Perlman
                                                                M. Umair
Expires: April 12, 2017                                  October 9, 2017

                       TRILL: ARP/ND Optimization


   This document describes mechanisms to optimize the ARP (Address
   Resolution Protocol) and ND (Neighbor Discovery) traffic in a TRILL
   campus. TRILL switches maintain a cache of IP/MAC address/Data Label
   bindings that are learned from ARP/ND requests and responses that
   pass through them. In many cases, this cache allows an edge RBridge
   to avoid flooding an ARP/ND request by either responding to it
   directly or by encapsulating it and unicasting it. Such optimization
   reduces packet flooding over a TRILL campus. 

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
   other groups may also distribute working documents as

   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


Yizhou, et al                                                   [Page 1]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

Copyright and License Notice

   Copyright (c) 2017 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
   ( 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/SEND Messages  . . . . . . . . . . . . . . . . .  5
     4.1 SEND Considerations  . . . . . . . . . . . . . . . . . . . .  6
     4.2 Address Verification . . . . . . . . . . . . . . . . . . . .  7
     4.3 Extracting Local End Station IP/MAC Mapping Information  . .  7
     4.4 Determine How to Reply to ARP/ND . . . . . . . . . . . . . .  8
     4.5 Determine How to Handle the ARP/ND Response  . . . . . . . . 10
   5 Handling of RARP (Reverse Address Resolution Protocol)
     Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6 Handling of DHCP messages  . . . . . . . . . . . . . . . . . . . 10
   7 Handling of Duplicate IP Addresses . . . . . . . . . . . . . . . 10
   8 RBridge ARP/ND Cache Liveness and MAC Mobility . . . . . . . . . 11
   9 Security Considerations  . . . . . . . . . . . . . . . . . . . . 12
     9.1 Data Plane Based Considerations  . . . . . . . . . . . . . . 12
     9.2 Directory Based Considerations . . . . . . . . . . . . . . . 13
     9.3 Use of the Confidence Level Feature  . . . . . . . . . . . . 13
   10 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13
   11 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 14
   12 References  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     12.1 Normative References  . . . . . . . . . . . . . . . . . . . 14
     12.2 Informative References  . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16


Yizhou, et al                                                   [Page 2]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

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

   DHCP           In this document refers to both DHCP for IPv4
   [RFC2131] and DHCPv6 [RFC3315]

   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

Yizhou, et al                                                   [Page 3]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   implementing the TRILL protocol.

   SEND           secure neighbor discovery [RFC3971]

   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. This section is a general discussion of this
   problem and is not intended to be normative.

   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
   [RFC8171], 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 a TRILL Campus, When all end-
   station MAC addresses are similarly known, it should be possible to
   suppress unknown unicast flooding 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 detect duplication of its IP address.

   Most of the end station hosts either send DHCP messages requesting an
   IP Address or 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

Yizhou, et al                                                   [Page 4]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   When complete directory information is available, the default data
   plane learning of MAC addresses of end station is not only
   unnecessary but could be harmful if there is learning based on frames
   with forged source addresses. Such data plane learning can be
   suppressed because TRILL already provides an option to disable data-
   plane learning from the source MAC address of end-station frames (see
   Section 5.3 of [RFC6325]).

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. The 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 RBridge Directory Assist
   Mechanisms [RFC8171] 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 edge RBridge
   has extracted the sender's IP/MAC address pair from the received data
   frame (either ARP or ND), it may save the information and then use
   the IA APPsub-TLV to link the IP and MAC addresses and 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 [RFC8171]. 

   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/SEND Messages

Yizhou, et al                                                   [Page 5]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   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.

   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/SEND message, it can
   perform the steps described within the sub-sections below. In
   particular, Section 4.4 describes the options for such an ingress
   handling an ARP/ND message and, in the cases where it forwards the
   message, Section 4.5 describes how to handle any response that may be
   returned due to the forwarded message.

   Section 4.3 describes the extraction of address information by an
   RBridge from ARP/ND messages it handles. Under some circumstances,
   this extraction may prompt verification with an end station. Section
   4.2 describes an optional use of ARP/ND messages originated by
   RBridges to verify addresses or liveness.

   As described in Section 4.1, SEND messages are not optimized by the
   mechanisms specified in this document but are snooped on.

4.1 SEND Considerations

   SEND (Secure Neighbor Discovery [RFC3971] is a method of securing ND
   that addresses the threats discussed in [RFC3756]. Typical TRILL
   campuses are inside data centers, Internet exchange points, or
   carrier facilities. These are generally controlled and protected
   environments where these threats are of less concern. Nevertheless,
   SEND provides an additional layer of protection.

   Secure SEND messages require knowledge of cryptographic keys. Methods
   of communicating such keys to RBridges for use in SEND are beyond the

Yizhou, et al                                                   [Page 6]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   scope of this document. Thus, using the optimizations in this
   document, RBridges do not attempt to construct SEND messages and are
   generally transparent to them. RBridges only construct ARP, RARP, or
   insecure ND messages, as appropriate. Nevertheless, RBridges
   implementing ARP/ND optimization SHOULD snoop on SEND messages to
   extract the addressing information that would be present if the SEND
   had been sent as an insecure ND message and is still present in the
   SEND message.

4.2 Address Verification

   RBridges may use ARP/ND to probe directly attached or remote end
   stations for address or liveness verification. This is typically most
   appropriate in less managed and/or higher mobility environments. In
   strongly managed environments, such as a typical data center, where a
   central orchestration/directory system has complete addressing
   knowledge [RFC7067], optimized ARP/ND responses can use that
   knowledge. In such cases, there is little reason for verification
   except for debugging operational problems or the like.

4.3 Extracting Local End Station IP/MAC Mapping Information 

   Edge RBridges extract and use information about the correspondence
   between local end station IP and MAC addresses from the ARP/ND
   messages those end stations send as described below. An apparent zero
   source IP address means that the end station is probing for duplicate
   IP addresses and messages with such a zero source IP address are not
   used for the extraction of IP/MAC address mapping information.

   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 (Section 4.2). RBridge SHOULD update the saved

Yizhou, et al                                                   [Page 7]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   triplet of {IP address, MAC address, ingress nickname} based on the
   verification results. 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/ND it

   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. If a push directory server is used, such information can be
   distributed as specified in [RFC8171].

4.4 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
   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. Within each
   lettered item, it is an implementation decision which numbered
   strategy to use for any particular ARP/ND query falling under that

   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/SEND 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

Yizhou, et al                                                   [Page 8]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

     querier when the response to the recently-launched query to that
     target is received.

     a.4  Reply to the querier based on directory information [RFC8171]
     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 ARP/ND/SEND request as per [RFC6325].

   (b) If the message is a generic ARP/ND/SEND 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 therefore only action b.1 is

     b.1. Flood the ARP/ND/SEND message as per [RFC6325].

     b.2. Use directory server to pull the information [RFC8171] and
     reply to the querier.

     b.3. Drop the message if there should be no response because the
     directory server gives authoritative information that the address
     being queried is non-existent.

   (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/SEND:

   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.


Yizhou, et al                                                   [Page 9]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

4.5 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.2 or to flood the request as per [RFC6325] and item a.5, then R2
   decapsulates the query, and initiates an ARP/ND query on the target's
   link. If and when 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 [RFC8171] if push directory server is in use. 

5 Handling of RARP (Reverse Address Resolution Protocol) Messages

   RARP [RFC903] uses the same packet format as ARP but a different
   Ethertype (0x8035) and opcode values. Its processing 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. 

6 Handling of DHCP messages

   When a newly connected end-station exchanges messages with a DHCP
   [RFC3315][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 using ESADI.

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.

Yizhou, et al                                                  [Page 10]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   Duplicate IP addresses can be detected when an existing active IP/MAC
   mapping gets modified. Also an edge RBridge may send a query called a
   DAD-query (Duplicate Address Detection query) asking about the IP
   address in question to the former owner of that IP address by using
   the MAC address formerly associated with that IP address. A DAD-query
   is a unicast ARP/ND message with sender IP in case of ARP (or
   a configurable IP address per RBridge 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, it may be a case of mobility
   and in any case the new IP entry will be confirmed and activated in
   its ARP/ND cache.

   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

   It is an implementation choice how to respond to a query for an
   address that is duplicated in the network when authoritative
   information is not available from a directory or configuration.
   Typically the information most recently snooped is returned.

8 RBridge ARP/ND Cache Liveness and MAC Mobility

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

   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
   has been learnt as local entry on RB1. If end-Station "A" moves to
   some other location (MAC/VM Mobility) and gets connected to edge-
   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-

Yizhou, et al                                                  [Page 11]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   label should update the entry to show reachability from RB2 instead
   of RB1.

   If an ARP/ND entry in the cache is not refreshed, then the RBridge
   connected to that end-station MAY send periodic refresh messages
   (ARP/ND "probes") to that end-station, so that the entries can be
   refreshed before they age out. The end-station would reply to the
   ARP/ND probe and the reply resets the corresponding entry age-timer.

9 Security Considerations

   There are generally two modes of learning the address information
   that is the basis of ARP/ND optimization: data plane mode and
   directory mode. The data plane mode is the traditional bridge address
   learning [802.1Q] that is also implemented in TRILL switches
   [RFC6325] and is discussed in Section 9.1. The directory mode uses
   data obtained from a directory [RFC8171] and is discussed in Section
   9.2. The TRILL confidence level feature, which can help arbitrate
   between conflicting address information, is discussed in Section 9.3.

   RBridges should rate limit of ARP/ND queries injected into the TRILL
   campus to limit some potential denial of service attacks.

9.1 Data Plane Based Considerations

   Generally speaking, when ARP/ND optimization is operating in the data
   plane mode, the information learned by RBridges is the same as that
   which is learned by end stations. Thus the answers generated by
   RBridges to the query messages being optimized are generally those
   that would be generated by end stations in the absence of
   optimization and the security considerations are those of the
   underlying ARP/ND protocols.

   RBridges that snoop on DHCPack messages respond to ARP/ND messages in
   essentially the same way that the end stations sending those DHCPack
   messages would. Thus, for Security Considerations of ARP/ND
   optimization for DHCP messages that may be snooped, see the Security
   Considerations sections of [RFC3315] and [RFC2131].

   Unless Secure ND (SEND [RFC3971]) is used, ARP and ND messages can be
   easily forged. Therefore the learning of MAC/IP addresses by RBridges
   from ARP/ND is hackable but is what is available for data plane
   learning without SEND. See Section 4.1 for SEND Considerations.

   Since end stations communicate with edge RBridges using Ethernet,
   some security improvement could be obtained by the use of [802.1AE]
   between end stations and edge RBridges. Such link security would

Yizhou, et al                                                  [Page 12]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   impose requirements on edge stations, while TRILL is generally
   designed to operate with unmodified, TRILL-ignorant end stations, and
   is beyond the scope of this document

   ARP/ND address mapping information learned locally at an RBridge can
   be distributed to other RBridges using the TRILL ESADI protocol that
   can be secured as specified in [RFC7357]. (ESADI is also used for
   push directories with flags in the data indicating whether data come
   from a directory or from data plane learning, as well as a confidence
   level (see Section 9.3).)

9.2 Directory Based Considerations

   ARP/ND optimization can be based on directory information [RFC8171].
   If the directory information is know to be trustworthy and complete,
   then trustworthy responses to ARP/ND queries can be entirely based on
   this information. This bounds the damage that forged ARP/ND messages
   can do to the local link between end stations and edge RBridges. (In
   TRILL, such a "link" can be a bridged LAN.)

   Of course, there can also be incomplete and/or un-reliable directory
   address mapping data. The network administrator can configure their
   TRILL campus to use such directory data in place of data plane
   learned data. Alternatively, such directory data can be used along
   with data plane learned arbitrated by confidence level as discussed
   in Section 9.3.

9.3 Use of the Confidence Level Feature

   An RBridge can use the confidence level in IA APPsub-TLV information
   received via ESADI or pull directory retrievals to determine the
   configured relative reliability of MAC/IP address mapping information
   from those sources and from locally learned address information.
   ESADI / push directory information can be secured as provided in
   [RFC7357] and pull directory information can be secured as provided
   in [RFC8171]. 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 it does so. Thus the implementer can, to some
   extent, cause sources that they know are more reliable to dominate
   those they know to be less reliable. How the implementer determines
   this is beyond the scope of this document.

10 IANA Considerations

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

Yizhou, et al                                                  [Page 13]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

11 Acknowledgments

   The authors would like to thank Igor Gashinsky and Sue Hares for
   their 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.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, July 2003.

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

   [RFC7357]  Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.

Yizhou, et al                                                  [Page 14]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

              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.

   [RFC8171]  Eastlake 3rd, D., Dunbar, L., Perlman, R., and Y. Li,
              "Transparent Interconnection of Lots of Links (TRILL):
              Edge Directory Assistance Mechanisms", RFC 8171, June

12.2 Informative References

   [802.1AE]  IEEE Std 802.1AE-2006, IEEE Standard for Local and
              metropolitan networks / Media Access Control (MAC)
              Security, 18 August 2006.

   [802.1Q]   IEE Std 8021Q-2014, IEEE Standard for Local and
              metropolitan area networks / Bridges and Bridged Networks,
              3 November 2014.

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, May 2004.

   [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.


Yizhou, et al                                                  [Page 15]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   [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.

   [RFC7067]  Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
              Gashinsky, "Directory Assistance Problem and High-Level
              Design Proposal", RFC 7067, November 2013.

Authors' Addresses

   Yizhou Li
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012

   Phone: +86-25-56625375

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

   Phone: +1-508-333-2270

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

   Phone: +1-469-277-5840

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


   Mohammed Umair
   Cessna Business Park, Kadubeesanahalli Village, Hobli,
   Sarjapur, Varthur Main Road, Marathahalli,

Yizhou, et al                                                  [Page 16]
INTERNET DRAFT         TRILL ARP/ND Optimization            October 2017

   Bengaluru, Karnataka 560087 India 


Yizhou, et al                                                  [Page 17]