Network Working Group                                         W. Cerveny
Internet-Draft                                            Arbor Networks
Intended status: Informational                                 R. Bonica
Expires: July 8, 2016                                   Juniper Networks
                                                         January 5, 2016

               Benchmarking IPv6 Neighbor Cache Behavior


   This document is a benchmarking instantiation of RFC 6583:
   "Operational Neighbor Discovery Problems" [RFC6583].  It describes a
   general testing procedure and measurements that can be performed to
   evaluate how the problems described in RFC 6583 may impact the
   functionality or performance of intermediate nodes.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 8, 2016.

Copyright Notice

   Copyright (c) 2016 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

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   ( 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Overview of Relevant NDP and Intermediate Node Behavior . . .   3
   4.  Test Setup  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Testing Interfaces  . . . . . . . . . . . . . . . . . . .   6
   5.  Modifiers (Variables) . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Frequency of NDP Triggering Packets . . . . . . . . . . .   6
   6.  Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Stale Entry Time Determination  . . . . . . . . . . . . .   6
       6.1.1.  General Testing Procedure . . . . . . . . . . . . . .   7
     6.2.  Neighbor Cache Exhaustion Determination . . . . . . . . .   7
       6.2.1.  General Testing Procedure . . . . . . . . . . . . . .   7
   7.  Measurements Explicitly Excluded  . . . . . . . . . . . . . .   8
     7.1.  DUT CPU Utilization . . . . . . . . . . . . . . . . . . .   8
     7.2.  Malformed Packets . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document is a benchmarking instantiation of RFC 6583:
   "Operational Neighbor Discovery Problems" [RFC6583].  It describes a
   general testing procedure and measurements that can be performed to
   evaluate how the problems described in RFC 6583 may impact the
   functionality or performance of intermediate nodes.

2.  Terminology

   Intermediate Node  A router, switch, firewall or any other device
      which separates end-nodes.  The tests in this document can be
      completed with any intermediate node which maintains a neighbor
      cache, although not all measurements and performance
      characteristics may apply.

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   Neighbor Cache  The neighbor cache is a database which correlates the
      link-layer address and the adjacent interface with an IPv6

   Neighbor Discovery  See Section 1 of RFC 4861 [RFC4861]

   Scanner Network  The network from which the scanning tester is

   Scanning Interface  The interface from which the scanning activity is

   Stale Entry Time  This is the duration for which a neighbor cache
      entry marked "Reachable" will continue to be marked "Reachable" if
      an update for the address is not received.

   Target Network  The network for which the scanning tests is targeted.

   Target Network Destination Interface  The interface that resides on
      the target network, which is primarily used to measure DUT
      performance while the scanning activity is occurring.

3.  Overview of Relevant NDP and Intermediate Node Behavior

   In a traditional network, an intermediate node must support a mapping
   between a connected node's IP address and the connected node's link-
   layer address and interface the node is connected to.  With IPv4,
   this process is handled by ARP [RFC0826].  With IPv6, this process is
   handled by NDP and is documented in [RFC4861].  With IPv6, when a
   packet arrives on one of an intermediate node's interfaces and the
   destination address is determined to be reachable via an adjacent

   1.  The intermediate node first determines if the destination IPv6
       address is present in its neighbor cache.

   2.  If the address is present in the neighbor cache, the intermediate
       node forwards the packet to the destination node using the
       appropriate link-layer address and interface.

   3.  If the destination IPv6 address is not in the intermediate node's
       neighbor cache:

       1.  An entry for the IPv6 address is added to the neighbor cache
           and the entry is marked "INCOMPLETE".

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       2.  The intermediate node sends a neighbor solicitation packet to
           the solicited-node multicast address on the interface
           considered on-link.

       3.  If a solicited neighbor advertisement for the IPv6 address is
           received by the intermediate node, the neighbor cache entry
           is marked "REACHABLE" and remains in this state for 15 to 45

       4.  If a neighbor advertisement is not received, the intermediate
           node will continue sending neighbor solicitation packets
           every second until either a neighbor solicitation is received
           or the maximum number of solicitations has been sent.  If a
           neighbor advertisement is not received in this period, the
           entry can be discarded.

   There are two scenarios where a neighbor cache can grow to a very
   large size:

   1.  There are a large number of real nodes connected via an
       intermediate node's interface and a large number of these nodes
       are sending and receiving traffic simultaneously.

   2.  There are a large number of addresses for which a scanning
       activity is occuring and no real node will respond to the
       neighbor solicitation.  This scanning activity can be
       unintentional or malicious.  In addition to maintaining the
       "INCOMPLETE" neighbor cache entry, the intermediate node must
       send a neighbor solicitation packet every second for the maximum
       number of socicitations.  With today's network link bandwidths, a
       scanning event could cause a lot of entries to be added to the
       neighbor cache and solicited for in the time that it takes for a
       neighbor cache entry to be discarded.

   An intermediate node's neighbor cache is of a finite size and can
   only accommodate a specific number of entries, which can be limited
   by available memory or a preset operating system limit.  If the
   maximum number of entries in a neighbor cache is reached, the
   intermediate node must either drop an existing entry to make space
   for the new entry or deny the new IP address to MAC address/
   interface mapping with an entry in the neighbor cache.  In an extreme
   case, the intermediate node's memory may become exhausted, causing
   the intermediate node to crash or begin paging memory.

   At the core of the neighbor discovery problems presented in RFC 6583
   [RFC6583], unintentional or malicious IPv6 traffic can transit the
   intermediate node that resembles an IP address scan similar to an
   IPv4-based network scan.  Unlike IPv4 networks, an IPv6 end network

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   is typically configured with a /64 address block, allowing for
   upwards of 2**64 addresses.  When a network node attempts to scan all
   the addresses in a /64 address block directly attached to the
   intermediate node, it is possible to create a huge amount of state in
   the intermediate node's neighbor cache, which may stress processing
   or memory resources.

   Section 7.1 of RFC 6583 recommends how intermediate nodes should
   behave when the neighbor cache is exceeded.  Section 6 of RFC 6583
   [RFC6583] recommends how damage from an IPv6 address scan may be
   mitigated.  Section 6.2 of RFC 6583 [RFC6583] discusses queue tuning.

4.  Test Setup

   The network needs to minimally have two subnets: one from which the
   scanner(s) source their scanning activity and the other which is the
   target network of the address scans.

   It is assumed that the latency for all network segments is neglible.
   By default, the target network's subnet shall be 64-bits in length,
   although some tests may involve increasing the prefix length.

   Although packet size shouldn't have a direct impact, packet per
   second (pps) rates will have an impact.  Smaller packet sizes should
   be utilized to facilitate higher packet per second rates.

   For purposes of this test, the packet type being sent by the scanning
   device isn't important, although most scanning applications might
   want to send packets that would elicit responses from nodes within a
   subnet (such as an ICMPv6 echo request).  Since it is not intended
   that responses be evoked from the target network node, such packets
   aren't necessary.

   At the beginning of each test the intermediate node should be
   initialized.  Minimally, the neighbor cache should be cleared.

   Basic format of test network.

+---------------+             +-----------+             +--------------+
|               |   Scanner   |           |   Target    |              |
|   Scanning    |-------------|    DUT    |-------------|Target Network|
| src interface |   Network   |           |   Network   |dst interface |
|               |             |           |             |              |
+---------------+             +-----------+             +--------------+

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4.1.  Testing Interfaces

   Two tester interfaces are configured for most tests:

   o  Scanning source (src) interface: This is the interface from which
      test packets are sourced.  This interface sources traffic to
      destination IPv6 addresses on the target network from a single
      link-local address, similar to how an adjacent intermediate node
      would transit traffic through the intermediate node.

   o  Target network destination (dst) interface: This interface
      responds to neighbor solicitations as appropriate and confirms
      when an intermediate node has forwarded a packet to the interface
      for consumption.  Where appropriate, the target network
      destination interface will respond to neighbor solicitations with
      a unique link-layer address per IPv6 address solicited.

5.  Modifiers (Variables)

5.1.  Frequency of NDP Triggering Packets

   The frequency of NDP triggering packets can be as high as the maximum
   packet per second rate that the scanner network will support (or is
   rated for).  However, it may not be necessary to send packets at a
   particularly high rate.  In fact, a non-benchmarking goal of testing
   could be to identify if the DUT is able to withstand scans at rates
   which otherwise would not impact the performance of the DUT.

   Optimistically, the scanning rate should be incremented until the
   DUT's performance begins deteriorating.  Depending on the software
   and system being used to implement the scanning, it may be
   challenging to achieve a sufficient rate.  Where this maximum
   threshold cannot be determined, the test results should note the
   highest rate tested and that DUT performance deterioration was not
   noticed at this rate.

   The lowest rate tested should be the rate for which packets can be
   expected to have an impact on the DUT -- this value is of course,

6.  Tests

6.1.  Stale Entry Time Determination

   This test determines the time interval when the intermediate node
   (DUT) identifies an address as stale.

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   RFC 4861, section 6.3.2 [RFC4861] states that an address can be
   marked "stale" at a random value between 15 and 45 seconds (as
   defined via constants in the RFC).  This test confirms what value is
   being used by the intermediate node.  Note that RFC 4861 states that
   this random time can be changed "at least every few hours."

6.1.1.  General Testing Procedure

   1.  Send a packet from the scanning source interface to an address in
       target network.  Observe that the intermediate node sends a
       neighbor solicitation to the solicited-node multicast address on
       the target network, for which tester destination interface should
       respond with a neighbor advertisement.  The intermediate node
       should create an entry in neighbor cache for the address, marking
       the address as "reachable".  As this point, the packet should be
       forwarded to the tester destination interface.

   2.  After the neighbor advertisement from the destination tester
       interface in step one, no more neighbor advertisements from the
       tester destination interface should be allowed.

   3.  Continue sending packets from the scanning source interface to
       the same address in the target network.

   4.  Note the time at which the DUT no longer forwards packets.  The
       stale timer value will be the period of time between when the DUT
       received the first neighbor advertisement above and the point at
       which the DUT no longer forwards packets for this flow to the
       tester destination interface.

6.2.  Neighbor Cache Exhaustion Determination

   Discover the point at which the neighbor cache is exhausted and
   evaluate intermediate node behavior when this threshold is reached.
   If possible, the stale timer value should be locked down to a large
   value.  A side-effect of this test is to confirm that intermediate
   node behaves correctly; in particular, it shouldn't crash.

   Note that some intermediate nodes may restrict the frequency of
   allowed neighbor discovery packets transmitted.  The maximum allowed
   packets per second must either be set to a value which doesn't impact
   the outcome of the test must allow for this restriction.

6.2.1.  General Testing Procedure

   1.  At a very fast rate, send packets incrementally to valid unique
       addresses in the target network, within stale entry time period.
       Simultaneously, send packets for addresses previously added to

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       the neighbor cache.  The neighbor cache has been exhausted when
       previously added addresses must be re-discovered with a neighbor
       solicitation (within the stale entry time period).

   2.  Observe what happens when one address greater than the maximum
       neighbor cache size ("n") is reached.  When "n+1" is reached, if
       either the first or most recent cache entry are dropped, this may
       be acceptable.

   3.  Confirm intermediate node doesn't crash when "n+1" is reached.

7.  Measurements Explicitly Excluded

   These are measurements which aren't recommended because of the
   itemized reasons below:

7.1.  DUT CPU Utilization

   This measurement relies on the DUT to provide utilization
   information, which is subjective.

7.2.  Malformed Packets

   This benchmarking test is not intended to test DUT behavior in the
   presence of malformed packets.

8.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

9.  Security Considerations

   Benchmarking activities as described in this memo are limited to
   technology characterization using controlled stimuli in a laboratory
   environment, with dedicated address space and the constraints
   specified in the sections above.

   The benchmarking network topology will be an independent test setup
   and MUST NOT be connected to devices that may forward the test
   traffic into a production network, or misroute traffic to the test
   management network.

   Further, benchmarking is performed on a "black-box" basis, relying
   solely on measurements observable external to the DUT/SUT.  Special

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   capabilities SHOULD NOT exist in the DUT/SUT specifically for
   benchmarking purposes.

   Any implications for network security arising from the DUT/SUT SHOULD
   be identical in the lab and in production networks.

10.  Acknowledgements

   Helpful comments and suggestions were offered by Al Morton, Joel
   Jaeggli, Nalini Elkins, Scott Bradner, Ram Krishnan, and Marius
   Georgescu on the BMWG e-mail list and at BMWG meetings.  Precise
   grammatical corrections and suggestions were offered by Ann Cerveny.

11.  References

11.1.  Normative References

   [RFC0826]  Plummer, D., "Ethernet Address Resolution Protocol: Or
              Converting Network Protocol Addresses to 48.bit Ethernet
              Address for Transmission on Ethernet Hardware", STD 37,
              RFC 826, DOI 10.17487/RFC0826, November 1982,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,

   [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,

   [RFC5180]  Popoviciu, C., Hamza, A., Van de Velde, G., and D.
              Dugatkin, "IPv6 Benchmarking Methodology for Network
              Interconnect Devices", RFC 5180, DOI 10.17487/RFC5180, May
              2008, <>.

   [RFC6583]  Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
              Neighbor Discovery Problems", RFC 6583,
              DOI 10.17487/RFC6583, March 2012,

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11.2.  Informative References

   [RFC7048]  Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
              Detection Is Too Impatient", RFC 7048,
              DOI 10.17487/RFC7048, January 2014,

Authors' Addresses

   Bill Cerveny
   Arbor Networks
   2727 South State Street
   Ann Arbor, MI  48104


   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20170


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