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Network Working Group                                          D. Saucez
Internet-Draft                          Universite catholique de Louvain
Intended status: Informational                                L. Iannone
Expires: January 3, 2012                Deutsche Telekom Laboratories AG
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                            July 2, 2011


                         LISP Threats Analysis
                     draft-ietf-lisp-threats-00.txt

Abstract

   This document analyzes the threats against the security of the
   Locator/Identifier Separation Protocol and proposes a set of
   recommendations to mitigate some of the identified security risks.

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 http://datatracker.ietf.org/drafts/current/.

   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 January 3, 2012.

Copyright Notice

   Copyright (c) 2011 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
   (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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  3
   4.  On-path Attackers  . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Off-Path Attackers: Reference Environment  . . . . . . . . . .  4
   6.  Data-Plane Threats . . . . . . . . . . . . . . . . . . . . . .  6
     6.1.  EID-to-RLOC Database Threats . . . . . . . . . . . . . . .  6
     6.2.  EID-to-RLOC Cache Threats  . . . . . . . . . . . . . . . .  7
       6.2.1.  EID-to-RLOC Cache poisoning  . . . . . . . . . . . . .  7
       6.2.2.  EID-to-RLOC Cache overflow . . . . . . . . . . . . . .  9
     6.3.  Attacks not leveraging on the LISP header  . . . . . . . .  9
     6.4.  Attacks leveraging on the LISP header  . . . . . . . . . . 10
       6.4.1.  Attacks using the Locator Status Bits  . . . . . . . . 10
       6.4.2.  Attacks using the Map-Version bit  . . . . . . . . . . 11
       6.4.3.  Attacks using the Nonce-Present and the Echo-Nonce
               bits . . . . . . . . . . . . . . . . . . . . . . . . . 12
       6.4.4.  Attacks using the ID Instance bits . . . . . . . . . . 13
   7.  Control Plane Threats  . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Attacks with Map-Request messages  . . . . . . . . . . . . 13
     7.2.  Attacks with Map-Reply messages  . . . . . . . . . . . . . 15
     7.3.  Gleaning Attacks . . . . . . . . . . . . . . . . . . . . . 15
   8.  Threats concerning Interworking  . . . . . . . . . . . . . . . 17
   9.  Threats with Malicious xTRs  . . . . . . . . . . . . . . . . . 18
   10. Security of the ALT Mapping System . . . . . . . . . . . . . . 20
   11. Threats concerning LISP-MS . . . . . . . . . . . . . . . . . . 21
     11.1. Map Server . . . . . . . . . . . . . . . . . . . . . . . . 21
     11.2. Map-Resolver . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Suggested Recommendations  . . . . . . . . . . . . . . . . . . 23
   13. Document Status and Plans  . . . . . . . . . . . . . . . . . . 25
   14. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   15. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   16. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26
   17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     17.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     17.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Appendix A.  Document Change Log . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28









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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  Introduction

   The Locator/ID Separation Protocol (LISP) is defined in
   [I-D.ietf-lisp].  The present document aims at identifying threats in
   the current LISP specification.  We also propose some recommendations
   on mechanisms that could improve the security of LISP against off-
   path attackers.  This document builds upon [I-D.bagnulo-lisp-threat].

   This document is split in two parts.  The first discusses the LISP
   data-plane and the second the LISP control-plane.

   The LISP data-plane consists of LISP packet encapsulation,
   decapsulation, and forwarding and includes the EID-to-RLOC Cache and
   EID-to-RLOC Database data structures used to perform these
   operations.

   The LISP control-plane consists in the mapping distribution system,
   which can be one of the mapping distribution systems proposed so far
   (e.g., [I-D.ietf-lisp], [I-D.ietf-lisp-alt], [I-D.ietf-lisp-ms],
   [I-D.meyer-lisp-cons], and [I-D.lear-lisp-nerd]), and the Map-
   Request, Map-Reply, Map-Register messages.

   This document does not consider all the possible uses of LISP as
   discussed in [I-D.ietf-lisp].  The document focuses on LISP unicast,
   including as well LISP Interworking [I-D.ietf-lisp-interworking],
   LISP-MS [I-D.ietf-lisp-ms], and briefly considers the ALT mapping
   system described in [I-D.ietf-lisp-alt].

   Furthermore, here we assume a generic IP service and do not discuss
   the difference from a security viewpoint between using IPv4 or IPv6.


3.  Definition of Terms

   The present document does not introduce any new term, compared to the
   main LISP specification.  For a complete list of terms please refer
   to [I-D.ietf-lisp].







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4.  On-path Attackers

   On-path attackers are attackers that are able to capture and modify
   all the packets exchanged between an ITR and an ETR.  To cope with
   such an attacker, cryptographic techniques such as those used by
   IPSec are required.  We do not consider that LISP has to cope with
   such attackers.

   Mobile IP has also considered time-shifted attacks from on-path
   attackers.  A time-shifted attack is an attack where the attacker is
   temporarily on the path between two communicating hosts.  While it is
   on-path, the attacker sends specially crafted packets or modifies
   packets exchanged by the communicating hosts in order to disturb the
   packet flow (e.g., by performing a man in the middle attack).  An
   important issue for time-shifted attacks is the duration of the
   attack once the attacker has left the path between the two
   communicating hosts.  We do not consider time-shifted attacks in this
   document.


5.  Off-Path Attackers: Reference Environment

   Throughout this document we consider the reference environment shown
   in the figure below.  There are two hosts attached to LISP routers:
   HA and HB.  HA is attached to the two LISP xTRs LR1 and LR2, which
   are attached to two different ISPs.  HB is attached to the two LISP
   xTRs LR3 and LR4.  HA and HB are the EIDs of the two hosts.  LR1,
   LR2, LR3, and LR4 are the RLOCs of the xTRs.























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                 +-----+
                 | HA  |
                 +-----+
                    | EID: HA
                    |
                -----------------
                    |          |
                 +-----+    +-----+
                 | LR1 |    | LR2 |
                 +-----+    +-----+
                    |          |
                    |          |
                 +-----+    +-----+
                 |ISP1 |    |ISP2 |
                 +-----+    +-----+
                    |          |
                 +----------------+     +-----+
                 |                |-----| SA  |
                 |                |     +-----+
                 |    Internet    |
                 |                |     +-----+
                 |                |-----| NSA |
                 +----------------+     +-----+
                    |          |
                 +-----+    +-----+
                 | LR3 |    | LR4 |
                 +-----+    +-----+
                    |          |
                -------------------
                               |
                               | EID: HB
                            +-----+
                            | HB  |
                            +-----+

                        Figure 1: Reference Network

   We consider two off-path attackers with different capabilities:

   SA  is an off-path attacker that is able to send spoofed packets,
       i.e., packets with a different source IP address than its
       assigned IP address.  SA stands for Spoofing Attacker.

   NSA is an off-path attacker that is only able to send packets whose
       source address is its assigned IP address.  NSA stands for Non
       Spoofing Attacker.

   It should be noted that with LISP, packet spoofing is slightly



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   different than in the current Internet.  Generally the term "spoofed
   packet" indicates a packet containing a source IP address which is
   not the one of the actual originator of the packet.  Since LISP uses
   encapsulation, the spoofed address can be in the outer header as well
   as in the inner header, this translates in two types of spoofing:

   EID Spoofing:  the originator of the packet puts in it a spoofed EID.
         The packet will be normally encapsulated by the ITR of the
         site.

   RLOC Spoofing:  the originator of the packet generates directly a
         LISP-encapsulated packet with a spoofed source RLOC.

   Note that the two types of spoofing are not mutually exclusive,
   rather all combinations are possible and can be used to perform
   different kind of attacks.

   In our reference environment, both SA and NSA attackers are capable
   of sending LISP encapsulated data packets and LISP control packets.
   This means that SA is able to perform both RLOC and EID spoofing
   while NSA can only perform EID spoofing.  They may also send other
   types of IP packets such as ICMP messages.  We assume that both
   attackers can query the LISP mapping system to obtain the mappings
   for both HA and HB.


6.  Data-Plane Threats

   This section discusses threats and attacks related to the LISP data-
   plane.  More precisely, we discuss the operations of encapsulation,
   decapsulation, and forwarding as well as the content of the EID-to-
   RLOC Cache and EID-to-RLOC Database as specified in the original LISP
   document ([I-D.ietf-lisp]).

   We start considering the two main data structures of LISP, namely the
   EID-to-RLOC Database and the EID-to-RLOC Cache.  Then, we look at the
   data plane attacks that can be performed by a spoofing off-path
   attacker (SA) and discuss how they can be mitigated by the LISP xTRs.
   In this analysis, we assume that the LR1 and LR2 (resp. LR3 and LR4)
   xTRs maintain a EID-to-RLOC Cache that contains the required mapping
   entries to allow HA and HB to exchange packets.

6.1.  EID-to-RLOC Database Threats

   The EID-to-RLOC Database on each xTR maintains the set of mappings
   related to the EID-Prefixes that are "behind" the xTR.  Where
   "behind" means that at least one of the xTR's globally-visible IP
   addresses is a RLOC for those EID-Prefixes.



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   As described in [I-D.ietf-lisp], the EID-to-RLOC Database content is
   determined by configuration.  This means that the only way to attack
   this data structure is by gaining privileged access to the xTR.  As
   such, it is out of the scope of LISP to propose any mechanism to
   protect routers and, hence, it is no further analyzed in this
   document.

6.2.  EID-to-RLOC Cache Threats

   A key component of the overall LISP architecture is the EID-to-RLOC
   Cache.  The EID-to-RLOC Cache is the data structure that stores the
   bindings between EID and RLOC (namely the "mappings") to be used
   later on.  Attacks against this data structure can happen either when
   the mappings are first installed in the cache (see also Section 7) or
   by corrupting (poisoning) the mappings already present in the cache.

6.2.1.  EID-to-RLOC Cache poisoning

   The content of the EID-to-RLOC Cache can be poisoned by spoofing LISP
   encapsulated packets.  Example of EID-to-RLOC Cache poisoning are:

   Fake mapping:  The cache contains entirely fake mappings that do not
         originate from an authoritative mapping server.  This can be
         achieved either through gleaning as described in Section 7.3 or
         by attacking the control-plane as described in Section 7.

   EID Poisoning:  The EID-Prefix in a specific mapping is not owned by
         the originator of the entry.  Similarly to the previous case,
         this can be achieved either through gleaning as described in
         Section 7.3 or by attacking the control-plane as described in
         Section 7.

   EID redirection/RLOC poisoning:  The EID-Prefix in the mapping is not
         bound to (located by) the set of RLOCs present in the mapping.
         This can result in packets being redirected elsewhere,
         eavesdropped, or even blackholed.  Note that not necessarily
         all RLOCs are fake/spoofed.  The attack works also if only part
         of the RLOCs, the highest priority ones, is compromised.
         Again, this can be achieved either through the gleaning as
         described in Section 7.3 or by attacking the control-plane as
         described in Section 7.

   Reachability poisoning:  The reachability information stored in the
         mapping could be poisoned, redirecting the packets to a subset
         of the RLOCs (or even stopping it if locator status bits are
         all set to 0).  If reachability information is not verified
         through the control-plane this attack can be simply achieved by
         sending a spoofed packet with swapped or all locator status



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         bits reset.  The same result can be obtained by attacking the
         control-plane as described in Section 7.  Depending on how the
         RLOC reachability information is stored on the router, the
         attack can impact only one mapping or all the mappings that
         share the same RLOC.

   Traffic Engineering information poisoning:  The LISP protocol defines
         two attributes associated to each RLOC in order to perform
         inbound Traffic Engineering (TE): namely priority and weight.
         By injecting fake TE attributes, the attacker is able to break
         load balancing policies and concentrate all the traffic on a
         single RLOC or put more load on a RLOC than what is expected,
         creating congestion.  It is even possible to block the traffic
         if all the priorities are set to 255.  Corrupting the TE
         attributes can be achieved by attacking the control-plane as
         described in Section 7.

   Mapping TTL poisoning:  The LISP protocol associates a Time-To-Live
         to each mapping that, once expired, allows to delete a mapping
         from the EID-to-RLOC Cache (or forces a Map-Request/Map-Reply
         exchange to refresh it if still needed).  By injecting fake TTL
         values, an attacker can either shrink the EID-to-RLOC Cache
         (using very short TTL), thus creating an excess of cache miss
         causing a DoS on the mapping system, or it can increase the
         size of the cache by putting very high TTL values, up to a
         cache overflow (see Section 6.2.2).  Corrupting the TTL can be
         achieved by attacking the control-plane as described in
         Section 7.  Long TTL can be use in fake mappings to increase an
         attack duration.

   Instance ID poisoning:  The LISP protocol allows to use a 24-bit
         identifier to select the forwarding table to use on the
         decapsulating ETR to forward the decapsulated packet.  By
         spoofing this attribute the attacker is able to redirect or
         blackhole inbound traffic.  Corrupting the Instance ID
         attribute can be achieved by attacking the control-plane as
         described in Section 7.

   Map-Version poisoning:  The LISP protocol allows to associate a
         version number to mappings ([I-D.ietf-lisp-map-versioning]).
         The LISP header can transport source and destination map-
         versions, describing which version of the mapping have been
         used to select the source and the destination RLOCs of the LISP
         encapsulated packet.  By spoofing this attribute the attacker
         is able to trigger Map-Request on the receiving ETR.
         Corrupting the Map-Version attribute can be achieved either by
         attacking the control-plane as described in Section 7 or by
         using spoofed packets as described in Section 6.4.2.



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   If the above listed attacks succeed, the attacker has the means of
   controlling the traffic.

6.2.2.  EID-to-RLOC Cache overflow

   Depending on how the EID-to-RLOC Cache is managed (e.g., LRU vs. LFU)
   and depending on its size, an attacker can try to fill the cache with
   fake mappings.  Once the cache is full, some mappings will be
   replaced by new fake ones, causing traffic disruption.

   This can be achieved either through the gleaning as described in
   Section 7.3 or by attacking the control-plane as described in
   Section 7.

   Another way to generate a EID-to-RLOC Cache overflow is by injecting
   mapping with a fake and very large TTL value.  In this case the cache
   will keep a large amount of mappings ending with a completely full
   cache.  This type of attack can also be performed through the
   control-plane.

6.3.  Attacks not leveraging on the LISP header

   We first consider an attacker that sends packets without exploiting
   the LISP header, i.e., with the N, L, E, V, and I bits reset
   ([I-D.ietf-lisp]).

   To inject a packet in the HA-HB flow, a spoofing off-path attacker
   (SA) can send a LISP encapsulated packet whose source is set to LR1
   or LR2 and destination LR3 or LR4.  The packet will reach HB as if
   the packet was sent by host HA.  This is not different from today's
   Internet where a spoofing off-path attacker may inject data packets
   in any flow.  Several existing techniques can be used by hosts to
   prevent such attacks from affecting established flows, e.g.,
   [RFC4301] and [I-D.ietf-tcpm-tcp-security].

   On the other hand, a non-spoofing off-path attacker (NSA) can only
   send a packet whose source address is set to its assigned IP address.
   The destination address of the encapsulated packet can be LR3 or LR4.
   When the LISP ETR that serves HB receives the encapsulated packet, it
   can consult its EID-to-RLOC Cache and verify that NSA is not a valid
   source address for LISP encapsulated packets containing a packet sent
   by HA.  This verification is only possible if the ETR already has a
   valid mapping for HA.  Otherwise, and to avoid such data packet
   injection attacks, the LISP ETR should reject the packet and possibly
   query the mapping system to obtain a mapping for the encapsulated
   source EID (HA).





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6.4.  Attacks leveraging on the LISP header

   The latest LISP draft [I-D.ietf-lisp] defines several flags that
   modify the interpretation of the LISP header in data packets.  In
   this section, we discuss how an off-path attacker could exploit this
   LISP header.

6.4.1.  Attacks using the Locator Status Bits

   When the L bit is set to 1, it indicates that the second 32-bits
   longword of the LISP header contains the Locator Status Bits.  In
   this field, each bit position reflects the status of one of the RLOCs
   mapped to the source EID found in the encapsulated packet.  In
   particular, a packet with the L bit set and all Locator Status Bits
   set to zero indicates that none of the locators of the encapsulated
   source EID are reachable.  The reaction of a LISP ETR that receives
   such a packet is not clearly described in [I-D.ietf-lisp].

   A spoofing off-path attacker (SA) can send a data packet with the L
   bit set to 1, all Locator Status Bits set to zero, a spoofed source
   RLOC (e.g.  LR1), destination LR3, and containing an encapsulated
   packet whose source is HA.  If LR3 blindly trust the Locator Status
   Bits of the received packet it will set LR1 and LR2 as unreachable,
   possibly disrupting ongoing communication.

   Locator Status Bits can be blindly trusted only in secure
   environments.  In the general unsecured Internet environment, the
   safest practice for xTRs is to confirm the reachability change
   through the control plane (e.g., RLOC probing).  In the above
   example, LR3 should note that something has changed in the Locator
   Status Bits and query the mapping system in order to confirm status
   of the RLOCs of the source EID.

   A similar attack could occur by setting only one Locator Status Bit
   to 1, e.g., the one that corresponds to the source RLOC of the
   packet.

   If a non-spoofing off-path attacker (NSA) sends a data packet with
   the L bit set to 1 and all Locator Status Bits set to zero, this
   packet will contain the source address of the attacker.  Similarly as
   in Section 6.3, if the xTR accepts the packet without checking the
   EID-to-RLOC Cache for a mapping that binds the source EID and the
   source RLOC of the received packet, then the same observation like
   for the the spoofing attacker (SA) apply.

   Otherwise, if the xTR does make the check through the EID-to-RLOC
   Cache, it should reject the packet because its source address is not
   one of the addresses listed as RLOCs for the source EID.



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   Nevertheless, in this case a Map-Request should be sent, which can be
   used to perform Denial of Service attacks.  Indeed an attacker can
   frequently change the Locator Status Bits in order to trigger a large
   amount of Map-Requests.  Rate limitation, as described in
   [I-D.ietf-lisp], does not allow to send high number of such a
   request, resulting in the attacker saturating the rate with these
   spoofed packets.

6.4.2.  Attacks using the Map-Version bit

   The Map-Version bit is used to indicate whether the low-order 24 bits
   of the first 32 bits word of the LISP header contain an Source and
   Destination Map-Version.  When a LISP ETR receives a LISP
   encapsulated packet with the Map-Version bit set to 1, the following
   actions are taken:

   o  It compares the Destination Map-Version found in the header with
      the current version of its own mapping, in the EID-to-RLOC
      Database, for the destination EID found in the encapsulated
      packet.  If the received Destination Map-Version is smaller (i.e.,
      older) than the current version, the ETR should apply the SMR
      procedure described in [I-D.ietf-lisp] and send a Map-Request with
      the SMR bit set.

   o  If a mapping exists in the EID-to-RLOC Cache for the source EID,
      then it compares the Map-Version of that entry with the Source
      Map-Version found in the header of the packet.  If the stored
      mapping is older (i.e., the Map-Version is smaller) than the
      source version of the LISP encapsulated packet, the xTR should
      send a Map-Request for the source EID.

   A spoofing off-path attacker (SA) could use the Map-Version bit to
   force an ETR to send Map-Request messages.  The attacker can retrieve
   the current source and destination Map-Version for both HA and HB.
   Based on this information, it can send a spoofed packet with an older
   Source Map-Version or Destination Map-Version.  If the size of the
   Map-Request message is larger than the size of the smallest LISP-
   encapsulated packet that could trigger such a message, this could
   lead to amplification attacks (see Section 7.1).  Fortunately,
   [I-D.ietf-lisp] recommends to rate limit the Map-Request messages
   that are sent by an xTR.  This prevents the amplification attack, but
   there is a risk of Denial of Service attack if an attacker sends
   packets with Source and Destination Map-Versions that frequently
   change.  In this case, the ETR could consume all its rate by sending
   Map-Request messages in response to these spoofed packets.

   A non-spoofing off-path attacker (NSA) cannot success in such an
   attack if the destination xTR rejects the LISP encapsulated packets



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   that are not sent by one of the RLOCs mapped to the included source
   EID.  If it is not the case, the attacker can be able to perform
   attacks concerning the Destination Map Version number as for the
   spoofing off-path attacker (SA).

6.4.3.  Attacks using the Nonce-Present and the Echo-Nonce bits

   The Nonce-Present and Echo-Nonce bits are used when verifying the
   reachability of a remote ETR.  Assume that LR3 wants to verify that
   LR1 receives the packets that it sends.  LR3 can set the Echo-Nonce
   and the Nonce-Present bits in LISP data encapsulated packets and
   include a random nonce in these packets.  Upon reception of these
   packets, LR1 will store the nonce sent by LR3 and echo it when it
   returns LISP encapsulated data packets to LR3.

   A spoofing off-path attacker (SA) could interfere with this
   reachability test by sending two different types of packets:

   1.  LISP data encapsulated packets with the Nonce-Present bit set and
       a random nonce and the appropriate source and destination RLOCs.

   2.  LISP data encapsulated packets with the Nonce-Present and the
       Echo-Nonce bits both set and the appropriate source and
       destination RLOCs.  These packets will force the receiving ETR to
       store the received nonce and echo it in the LISP encapsulated
       packets that it sends.

   The first type of packet should not cause any major problem to ITRs.
   As the reachability test uses a 24 bits nonce, it is unlikely that an
   off-path attacker could send a single packet that causes an ITR to
   believe that the ETR it is testing is reachable while in reality it
   is not reachable.  To increase the success likelihood of such attach,
   the attacker should created a massive amount of packets carrying all
   possible nonce values.  However, "flood attack" can be easily
   detected and blocked.

   The second type of packet could be exploited to create a Denial of
   Service attack against the nonce-based reachability test.  Consider a
   spoofing off-path attacker (SA) that sends a continuous flow of
   spoofed LISP data encapsulated packets that contain the Nonce-Present
   and the Echo-Nonce bit and each packet contains a different random
   nonce.  The ETR that receives such packets will continuously change
   the nonce that it returns to the remote ITR.  If the remote ITR
   starts a nonce-reachability test, this test may fail because the ETR
   has received a spoofed LISP data encapsulated packet with a different
   random nonce and never echoes the real nonce.  In this case the ITR
   will consider the ETR not reachable.  The success of this test will
   of course depend on the ratio between the amount of packets sent by



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   the legitimate ITR and the spoofing off-path attacker (SA).

   Packets sent by a non-spoofing off-path attacker (NSA) can cause
   similar problem if no check is done with the EID-to-RLOC Cache (see
   Section 6.3 for the EID-to-RLOC Cache check).  Otherwise, if the
   check is performed the packets will be rejected by the ETR that
   receives them and cannot cause problems.

6.4.4.  Attacks using the ID Instance bits

   LISP allows to carry in its header a 24-bits value called "Instance
   ID" and used on the ITR to indicate which private AFI has been used
   for encapsulation, while on the ETR can be used to select the
   forwarding table used for forwarding the decapsulated packet.

   Even if an off-path attacker could randomly guess a valid Instance ID
   value, there is no LISP specific problem.  Obviously the attacker
   could be now able to reach hosts that are only reachable through the
   routing table identified by the attacked Instance ID, however, end-
   system security is out of the scope of this document.  Nevertheless,
   access lists can be configured to protect the network from Instance
   ID based attacks.


7.  Control Plane Threats

   In this section, we discuss the different types of attacks that can
   occur when an off-path attacker sends control plane packets.  We
   focus on the packets that are sent directly to the ETR and do not
   analyze the particularities of a LISP mapping system.  The ALT
   mapping system is discussed in Section 10.

7.1.  Attacks with Map-Request messages

   An off-path attacker could send Map-Request packets to a victim ETR.
   In theory, a Map-Request packet is only used to solicit an answer and
   as such it should not lead to security problems.  However, the LISP
   specification [I-D.ietf-lisp] contains several particularities that
   could be exploited by an off-path attacker.

   The first possible exploitation is the P bit.  The P bit is used to
   probe the reachability of remote ETRs in the control plane.  In our
   reference environment, LR3 could probe the reachability of LR1 by
   sending a Map-Request with the P bit set.  LR1 would reply by sending
   a Map-Reply message with the P bit set and the same nonce as in the
   Map-Request message.

   A spoofing off-path attacker (SA) could use the P bit to force a



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   victim ETR to send a Map-Reply to the spoofed source address of the
   Map-Request message.  As the Map-Reply can be larger than the Map-
   Request message, there is a risk of amplification attack.
   Considering only IPv6 addresses, a Map-Request can be as small as 40
   bytes, considering one single ITR address and no Mapping Protocol
   Data.  The Map-Reply instead has a size of O(12 + (R * (28 + N *
   24))) bytes, where N is the maximum number of RLOCs in a mapping and
   R the maximum number of records in a Map-Reply.  Since up to 255
   RLOCs can be associated to an EID-Prefix and 255 records can be
   stored in a Map-Reply, the maximum size of a Map-Reply is thus above
   1 MB showing a size factor of up to 39,193 between the message sent
   by the attacker and the message sent by the ETR.  These numbers are
   however theoretical values not considering transport layer
   limitations and it is more likely that the reply will contain only on
   record with at most a dozen of locators, giving an amplification
   factor around 8.

   Any ISP with a large number of potential RLOCs for a given EID-Prefix
   should carefully ponder the best trade-off between the number of
   RLOCs through which it wants that the EID is reachable and the
   consequences that an amplification attack can produce.

   It should be noted that the maximum rate of Map-Reply messages should
   apply to all Map-Replies and also be associated to each destination
   that receives Map-Reply messages.  Otherwise, a possible
   amplification attack could be launched by a spoofing off-path
   attacker (SA) as follows.  Consider an attacker SA and and EID-Prefix
   p/P and a victim ITR.  To amplify a Denial of Service attack against
   the victim ITR, SA could send spoofed Map-Request messages whose
   source EID addresses are all the addresses inside p/P and source RLOC
   address is the victim ITR.  Upon reception of these Map-Request
   messages, the ETR would send large Map-Reply messages for each of the
   addresses inside p/P back to the victim ITR.

   If a non-spoofing off-path attacker (NSA) sends a Map-Request with
   the P bit set, it will receive a Map-Reply with the P bit set.  This
   does not raise security issues besides the usual risk of overloading
   a victim ETR by sending too many Map-Request messages.

   The Map-Request message may also contain the SMR bit.  Upon reception
   of a Map-Request message with the SMR bit, an ETR must return to the
   source of the Map-Request message a Map-Request message to retrieve
   the corresponding mapping.  This raises similar problems as the P bit
   discussed above except that as the Map-Request messages are smaller
   than Map-Reply messages, the risk of amplification attacks is
   reduced.  This is not true anymore if the ETR append to the Map-
   Request messages its own Map-Records.  This mechanism is meant to
   reduce the delay in mapping distribution since mapping information is



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   provided in the Map-Request message.

   Furthermore, appending Map-Records to Map-Request messages represents
   a major security risk since an off-path attacker could generate a
   (spoofed or not) Map-Request message and include in the Map-Reply
   portion of the message mapping for EID prefixes that it does not
   serve.  This could lead to various types of redirection and denial of
   service attacks.  An xTR should not process the Map-Records
   information that it receives in a Map-Request message.

7.2.  Attacks with Map-Reply messages

   In this section we analyze the attacks that could occur when an off-
   path attacker sends directly Map-Reply messages to ETRs without using
   one of the proposed LISP mapping systems.

   There are two different types of Map-Reply messages:

   Positive Map-Reply:  This messages contain a Map-Record binding an
         EID-Prefix to one or more RLOCs.

   Negative Map-Reply:  This messages contain a Map-Record for an EID-
         Prefix with an empty locator-set and specifying an action,
         which may be either Drop, Natively forward, or Send Map-
         Request.

   Positive Map-Reply messages are used to map EID-Prefixes onto RLOCs.
   Negative Map-Reply messages are used to support PTR and interconnect
   the LISP Internet with the legacy Internet.

   Most of the security of the Map-Reply messages depend on the 64 bits
   nonce that is included in a Map-Request and returned in the Map-
   Reply.  An ETR must never accept a Map-Request message whose nonce
   does not match one of the pending Map-Request messages.  If an ETR
   does not accept Map-Reply messages with an invalid nonce, the risk of
   attack is very small given the size of the nonce (64 bits).

   Note, however, that the nonce only confirms that the Map-Reply was
   sent by the ETR that received the Map-Request.  It does not validate
   the content of the Map-Reply message.

7.3.  Gleaning Attacks

   A third type of attack involves the gleaning mechanism proposed in
   [I-D.ietf-lisp] and discussed in [Saucez09].  In order to reduce the
   time required to obtain a mapping, [I-D.ietf-lisp] allows an ITR to
   learn a mapping from the LISP data encapsulated packets and the Map-
   Request packets that it receives.  LISP data encapsulated packet



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   contains a source RLOC, destination RLOC, source EID and destination
   EID.  When a ITR receives a data encapsulated packet coming from a
   source EID for which it does not already know a mapping, it may
   insert the mapping between the source RLOC and the source EID in its
   EID-to-RLOC Cache.  Gleaning can also be used when an ITR receives a
   Map-Request as the Map-Request also contains a source EID address and
   a source RLOC.  Once a gleaned entry has been added to the cache, the
   LISP ITR sends a Map-Request to retrieve the mapping for the gleaned
   EID from the mapping system.  [I-D.ietf-lisp] recommends to store the
   gleaned entries for only a few seconds.

   The first risk of gleaning is the ability to temporarily hijack an
   identity.  Consider an off-path attacker that wants to temporarily
   hijack host HA's identity and send packets to host HB with host HA's
   identity.  If the xTRs that serve host HB do not store a mapping for
   host HA, a non-spoofing off-path attacker (NSA) could send a LISP
   encapsulated data packet to LR3 or LR4.  The ETR will store the
   gleaned entry and use it to return the packets sent by host HB to the
   attacker.  In parallel, the ETR will send a Map-Request to retrieve
   the mapping for HA.  During a few seconds or until the reception of
   the Map-Reply, host HB will exchange packets with the attacker that
   has hijacked HA's identity.  Note that the attacker could in parallel
   send lots of Map-Requests or lots of LISP data encapsulated packets
   with random sources to force the xTR that is responsible for host HA
   to send lots of Map-Request messages in order to force it to exceed
   its rate limit for control plane messages.  This could further delay
   the arrival of the Map-Reply message on the requesting ETR.

   Gleaning also introduces the possibility of a man-in-the-middle
   attack.  Consider an off-path attacker that knows that hosts HA and
   HB that reside in different sites will exchange information at time
   t.  An off-path attacker could use this knowledge to launch a man-in-
   the-middle attack if the xTRs that serve the two hosts do not have
   mapping for the other EID.  For this, the attacker sends to LR1
   (resp. LR3) a LISP data encapsulated packet whose source RLOC is its
   IP address and contains an IP packet whose source is set to HB (resp.
   HA).  The attacker chooses a packet that will not trigger an answer,
   for example the last part of a fragmented packet.  Upon reception of
   these packets, LR1 and LR3 install gleaned entries that point to the
   attacker.  As explained above, the attacker could, at the same time,
   send lots of packets to LR1 and LR3 to force them to exhaust their
   control plane rate limit.  This will extend the duration of the
   gleaned entry.  If host HA establishes a flow with host HB at that
   time, the packets that they exchange will first pass through the
   attacker.

   In both cases, the attack only lasts for a few seconds (unless the
   attacker is able to exhaust the rate limitation).  However it should



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   be noted that today a large amount of packets may be exchanged during
   even a small fraction of time.


8.  Threats concerning Interworking

   [I-D.ietf-lisp-interworking] defines two network elements to allow
   LISP and non-LISP sites to communicate, namely the Proxy-ITR and the
   Proxy-ETR.  The Proxy-ITR encapsulates traffic from non-LISP sites in
   order to forward it toward LISP sites, while the Proxy-ETR
   decapsulates traffic arriving from LISP sites in order to forward it
   toward non-LISP sites.  For these elements some of the attack based
   on the LISP specific header are not possible, for the simple reason
   that some of the fields cannot be used due to the unidirectional
   nature of the traffic.

   The Proxy-ITR has functionalities similar to the ITR, however, its
   main purpose is to encapsulate packets arriving from the DFZ in order
   to reach LISP sites.  This means that it is no bound to any
   particular EID-Prefix, hence no mapping exists and no mapping can be
   configured in the EID-to-RLOC Database.  This means that the Proxy-
   ITR element itself is not able, to check whether or not the arriving
   traffic has the right to be encapsulated or not.  To limit such an
   issue it is recommended to use the current practice based on
   firewalls and ACLs on the machine running the Proxy-ITR service.  On
   the other side, the Proxy-ITR is meant to encapsulate only packets
   that are destined to one of the LISP sites it is serving.  This is
   the case for instance for a service provider selling Proxy-ITR
   services.  For this purpose a static EID-to-RLOC Cache can be
   configured in order to encapsulate only valid packets.  In case of a
   cache-miss no Map-Request needs to be sent and the packet can be
   silently dropped.

   The Proxy-ETR has functionalities similar to the ETR, however, its
   main purpose is to inject un-encapsulated packet in the DFZ in order
   to reach non-LISP-Sites.  This means that since there is no specific
   EID-Prefix downstream, it has no EID-to-RLOC Database that can be
   used to check whether or not the destination EID is part of its
   domain.  In order to avoid for the Proxy-ETR to be used as relay in a
   DoS attack it is preferable to configure the EID-to-RLOC Cache with
   static entries used to check if an encapsulated packet coming from a
   specific RLOC and having a specific source EID is actually allowed to
   transit through the Proxy-ETR.  This is also important for services
   provider selling Proxy-ETR service to actually process only packets
   arriving from its customers.  However, in case of cache-miss no Map-
   Request needs to be sent, rather the packet can be silently dropped
   since it is not originating from a valid site.  The same drop policy
   should be used for packets with an invalid source RLOC or a valid



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   source RLOC but an invalid EID.


9.  Threats with Malicious xTRs

   In this section, we discuss the threats that could be caused by
   malicious xTRs.  We consider the reference environment below where
   EL1 is a malicious or compromised xTR.  This malicious xTR serves a
   set of hosts that includes HC.  The other xTR and hosts in this
   network play the same role as in the reference environment described
   in Section 5.

                 +-----+
                 | HA  |
                 +-----+
                    | EID: HA
                    |
                -----------------
                    |          |
                 +-----+    +-----+
                 | LR1 |    | LR2 |
                 +-----+    +-----+
                    |          |
                    |          |
                 +-----+    +-----+
                 |ISP1 |    |ISP2 |
                 +-----+    +-----+
                    |          |
                 +----------------+     +-----+  |
                 |                |-----| EL1 |--|
                 |                |     +-----+  |
                 |    Internet    |              |  +-----+
                 |                |              |--| HC  |
                 |                |              |  +-----+
                 +----------------+                 EID: HC
                    |          |
                 +-----+    +-----+
                 | LR3 |    | LR4 |
                 +-----+    +-----+
                    |          |
                -------------------
                               |
                               | EID: HB
                            +-----+
                            | HB  |
                            +-----+

              Figure 2: Malicious xTRs' Reference Environment



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   Malicious xTRs are probably the most serious threat to the LISP
   control plane from a security viewpoint.  To understand the problem,
   let us consider the following scenario.  Host HC and HB exchange
   packets with host HA.  As all these hosts reside in LISP sites, LR1
   and LR2 store mappings for HB and HC.  Thus, these xTRs may need to
   exchange LISP control plane packets with EL1, e.g., to perform
   reachability tests or to refresh expired mappings (e.g., if HC's
   mapping has a small TTL).

   A first threat against the LISP control plane is when EL1 replies to
   a legitimate Map-Request message sent by LR1 or LR2 with a Map-Reply
   message that contains an EID-Prefix that is larger than the prefix
   owned by the site attached to EL1.  This could allow EL1 to attract
   packets destined to other EIDs than the EIDs that are attached to
   EL1.  This attack is called an "overclaiming" attack.
   [I-D.maino-lisp-sec] proposes a solution to protect LISP against
   overclaiming attacks under the assumption that the mapping system can
   be trusted.

   Another possible attack is a Denial of Service attack by sending a
   Negative Map-Reply message for a coarser prefix without any locator
   and with the Drop action.  Such a Negative Map-Reply indicates that
   the ETR that receives it should discard all packets.  The current
   LISP specification briefly discusses this problem [I-D.ietf-lisp],
   but the proposed solutions does not solve the problem.

   Another concern with malicious xTRs is the possibility of Denial of
   Service attacks.  A first attack is the flooding attack that was
   described in [I-D.bagnulo-lisp-threat].  This attack allows a
   malicious xTR to redirect traffic to a victim.  The malicious xTR
   first defines a mapping for HC with two RLOCs: its own RLOC (EL1) and
   the RLOC of the victim (e.g., LR3).  The victim's RLOC is set as
   unreachable in the mapping.  HC starts a large download from host HA.
   Once the download starts, the malicious xTR updates its Locator
   Status Bits, changes the mapping's version number or sets the SMR bit
   such that LR1 updates its EID-to-RLOC Cache to send all packets
   destined to HC to the victim's RLOC.  Instead of downloading from HA,
   the attacker could also send packets that trigger a response (e.g.,
   ICMP, TCP SYN, DNS request, ...) to HA.  HA would then send its
   response and its xTR would forward it to the victim's RLOC.

   An important point to note about this flooding attack is that it
   reveals a potential problem in the LISP architecture.  A LISP ITR
   relies on the received mapping and possible reachability information
   to select the RLOC of the ETR that it uses to reach a given EID or
   block of EIDs.  However, if the ITR made a mistake, e.g., due to
   configuration, implementation or other types of errors and has chosen
   a RLOC that does not serve the destination EID, there is no easy way



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   for the LISP ETR to inform the ITR of its mistake.  A possible
   solution could be to force a ETR to perform a reachability test with
   the selected ITR as soon as it selects it.  This will be analyzed in
   the next version of this document.


10.  Security of the ALT Mapping System

   One of the assumptions in [I-D.ietf-lisp] is that the mapping system
   is more secure than sending Map-Request and Map-Reply messages
   directly.  We analyze this assumption in this section by analyzing
   the security of the ALT mapping system.

   The ALT mapping system is basically a manually configured overlay of
   GRE tunnels between ALT routers.  BGP sessions are established
   between ALT routers that are connected through such a tunnel.  An ALT
   router advertises the EID prefixes that it serves over its BGP
   sessions with neighboring ALT routers and the EID-Prefixes that it
   has learned from neighboring ALT routers.

   The ALT mapping system is in fact a discovery system that allows any
   ALT router to discover the ALT router that is responsible for a given
   EID-Prefix.  To obtain a mapping from the ALT system, an ITR sends a
   packet containing a Map-Request on the overlay.  This Map-Request is
   sent inside a packet whose destination is the requested EID.  The
   Map-Request is routed on the overlay until it reaches the ALT router
   that advertised initially the prefix that contains the requested EID.
   This ALT router then replies directly by sending a Map-Reply to the
   RLOC of the requesting ITR.

   The security of the ALT mapping system depends on many factors,
   including:

   o  The security of the intermediate ALT routers.

   o  The validity of the BGP advertisements sent on the ALT overlay.

   Unfortunately, experience with BGP on the global Internet has shown
   that BGP is subject to various types of misconfiguration problems and
   security attacks.  The SIDR working group is developing a more secure
   inter-domain routing architecture to solve this problem
   ([I-D.ietf-sidr-arch]).

   The security of the intermediate ALT routers is another concern.  A
   malicious intermediate ALT router could manipulate the received BGP
   advertisements and also answer to received Map-Requests without
   forwarding them to their final destination on the overlay.  This
   could lead to various types of redirection attacks.  Note that in



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   contrast with a regular IP router that could also manipulate in
   transit packets, when a malicious or compromised ALT router replies
   to a Map-Request, it can redirect legitimate traffic for a long
   period of time by sending an invalid Map-Reply message.  Thus, the
   impact of a malicious ALT router could be much more severe than a
   malicious router in today's Internet.


11.  Threats concerning LISP-MS

   LISP-MS ([I-D.ietf-lisp-ms] specifies two network elements, namely
   the Map Server and the Map-Resolver, that are meant to be used by
   xTRs to access the mapping system.  The advantage is clearly the fact
   that even if the mapping system changes in time xTRs do not need to
   change anything since they deal only with Map Servers and Map-
   Resolvers.  This includes the security aspects, since no change in
   the local security policies is needed.

11.1.  Map Server

   Map Server is used to dispatch Map-Request coming from the mapping
   system to ETRs that are authoritative for the EID in the request.  To
   this end it is necessary that ETRs register their mappings to the Map
   Server.  This allows the Map Server to know toward which ETR to
   forward Map-Requests and also to announce the EID-prefix of the
   mapping in the mapping system.

   LISP uses a shared key approach in order to protect the Map Server
   and grant registration rights only to ETRs that have a valid key.
   Shared key must be used to protect both the registration message and
   the Map-Notify message when used.  The mechanism used to share the
   key between a MS and an ETRs must be secured to avoid that a
   malicious nodes catch the key and uses it to send forged Map-Register
   message to the MS.  A forged Map-Register message can be use to
   attract Map-Request and thus provide invalid Map-Replies or the
   redirect Map-Requests to a target to mount a DoS attack.

   More subtle attacks can be carried out only in the case of malicious
   ETRs.  A malicious ETR can register an invalid RLOC to divert Map-
   Requests to a target ETR and succeed a DoS attack on it.  To avoid
   this kind of attack, the Map Server must check that the registered
   RLOCs belongs to ETRs authoritative for the registered EID prefix.
   Such check can be done by sending and explicit Map-Request for the
   EID to the ETRs in the mapping and check that replies with a Map-
   Reply.  If the ETRs return a valid Map-Reply, the RLOC belongs to an
   authoritative ETR.  Note that this does not protect against malicious
   ETRs that create forged Map-Replies.  Stronger techniques for RLOC
   check are presented in [I-D.saucez-lisp-mapping-security].



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   Similarly to the previous case, a malicious ETR can register an
   invalid EID-prefix to attract Map-Requests or to redirect them to a
   target to mount a DoS attack.  To avoid this kind of attack, the Map
   Server must check that the prefixes registered by an ETR belong to
   that ETR.  One method could be to manually configure EID-prefix
   ranges that can be announced by ETRs.
   [I-D.saucez-lisp-mapping-security] present alternative techniques to
   verify the prefix claimed by an ETR.

11.2.  Map-Resolver

   Map-Resolvers receive Map-Requests, typically from ITRs, and use the
   mapping system to find a mapping for the EID in the Map-Request.  It
   can work in two modes:

   Non-Caching Mode:  The resolver just forwards the Map-Request to the
         mapping system, which will take care of delivering the request
         to an authoritative ETR.  The latter will send back a Map-Reply
         directly to the ITR that has originally issued the request.

   Caching Mode:  The resolver will generate a new Map-Request and send
         it to the mapping system.  In this way it will receive the
         corresponding reply, store a local copy in a cache, and send
         back a reply to the original requester.  Since all requested
         mappings are locally cached, before actually making a request
         to the mapping system it performs a lookup in the local cache
         and in case of an hit, it send back a reply without querying
         the mapping system.

   In its basic mode, i.e., non-caching mode, the Map-Resolver does not
   keep state, hence, the only direct form of attack is a DoS attack,
   where an attacker (or a group of attackers) can try to exhaust
   computational power by flooding the resolver with requests.  Common
   filtering techniques and BCP against DoS attacks can be applied in
   this case.

   Nonetheless, resolvers can be used by attackers as relay for DoS
   attacks against xTRs.  An off-path spoofing attacker can generate a
   high load of requests to a set of resolvers, hence distributing the
   load in order to avoid to be blocked.  All this requests can use a
   specific EID that makes all the requests to be forwarded to a
   specific ETR, which, as a result, will be victim of a DDoS attack.
   Similarly, the attacker can use a spoofed source address making all
   the replies to converge to one single ITR, which, as a result, will
   be victim of a DDoS attack.  Such scenarios are not specific to LISP,
   but rather a common problem of every query infrastructure, hence the
   same BCP can be applied in order to limit the attacks.




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   When functioning in caching-mode, the resolver will use the same type
   of cache than ITRs.  Due to its similarity with the ITRs' cache the
   analysis provided in Section 6.2 holds also in this case.  However,
   an important difference exists: this cache is not used for packet
   encapsulation but only for quick replies when new requests arrive.
   Therefore, as the caching-mode is only an optimization, the attacks
   that tends to fill the MR cache have a less severe impact on the
   traffic.

   The question may arise on whether a Kaminsky-like attack is possible
   for an off-path attacker against ITRs sending requests to a certain
   resolver.  The 64-bits nonce present in every message has been
   introduced in the LISP specification to avoid such kind of attack.
   There has been discussion within the LISP Working Group on the
   optimal size of the nonce, and it seems that 64-bits provides
   sufficient protection.

   A possible way to limit the above-described attacks is to introduce
   strong identification in the Map-Request/Map-Reply by using the
   Encapsulated Control Message with authentication enabled.


12.  Suggested Recommendations

   To mitigate the impact of attacks against LISP, the following
   recommendations should be followed.

   First, the use of some form of filtering can help in avoid or at
   least mitigate some types of attacks.

   o  On ETRs, packets should be decapsulated only if the destination
      EID is effectively part of the EID-Prefix downstream the ETR.
      Further, still on ETRs, packets should be decapsulated only if a
      mapping for the source EID is present in the EID-to-RLOC Cache and
      has been obtained through the mapping system (not gleaned).

   o  On ITRs, packets should be encapsulated only if the source EID is
      effectively part of the EID-Prefix downstream the ITR.  Further,
      still on ITRs, packets should be encapsulated only if a mapping
      obtained from the mapping system is present in the EID-to-RLOC
      Cache (no Data-Probing).

   Note that this filtering, since complete mappings need to be
   installed in both ITRs and ETRs, can introduce a higher connection
   setup latency and hence potentially more packets drops due to the
   lack of mappings in the EID-to-RLOC Cache.

   While the gleaning mechanism allows to start encapsulating packets to



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   a certain EID in parallel with the Map-Request to obtain a mapping
   when a new flow is established, it creates important security risks
   since it allows attackers to perform identity hijacks.  Although the
   duration of these identity hijacks is limited (except the case of
   rate limitation exhaustion), their impact can be severe.  A first
   option would be to disable gleaning until the security concerns are
   solved.  A second option would be to strictly limit the number of
   packets that can be forwarded via a gleaned entry.  Overall the
   benefits of gleaning, i.e., avoiding the loss of the first packet of
   a flow, seems very small compared to the associated security risks.
   Furthermore, measurements performed in data centers show that today's
   Internet often operate with packet loss ratio of 1 or 2 percentage
   ([Chu]).  These packet loss ratio are probably already orders of
   magnitude larger than the improvement provided by the gleaning
   mechanism.

   With the increasing deployment of spoofing prevention techniques such
   as [RFC3704] or SAVI [SAVI], it can be expected that attackers will
   become less capable of sending packets with a spoofed source address.
   To prevent packet injection attacks from non-spoofing attackers
   (NSA), ETRs should always verify that the source RLOC of each
   received LISP data encapsulated packet corresponds to one of the
   RLOCs listed in the mappings for the source EID found in the inner
   packet.  An alternative could be to use existing IPSec techniques
   [RFC4301] and when necessary including perhaps [RFC5386] to establish
   an authenticated tunnel between the ITR and the ETR.

   [I-D.ietf-lisp] recommends to rate limit the control messages that
   are sent by a xTR.  This limit is important to deal with denial of
   service attacks.  However, a strict limit, e.g., implemented with a
   token bucket, on all the Map-Request and Map-Reply messages sent by a
   xTR is not sufficient.  A xTR should distinguish between different
   types of control plane packets:

   1.  The Map-Request messages that it sends to refresh expired mapping
       information.

   2.  The Map-Request messages that it sends to obtain mapping
       information because one of the served hosts tried to contact an
       external EID.

   3.  The Map-Request messages that it sends as reachability probes.

   4.  The Map-Reply messages that it sends as response to reachability
       probes.

   5.  The Map-Request messages that it sends to support gleaning.




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   These control plane messages are used for different purposes.  Fixing
   a global rate limit for all control plane messages increases the risk
   of Denial of Service attacks if a single type of control plane
   message can exceed the configured limit.  This risk could be
   mitigated by either specifying a rate for each of the five types of
   control plane messages.  Another option could be to define a maximum
   rate for all control plane messages, and prioritize the control plane
   messages according to the list above (with the highest priority for
   message type 1).

   In [I-D.ietf-lisp], there is no mechanism that allows a xTR to verify
   the validity of the content a Map-Reply message that it receives.
   Besides the attacks discussed earlier in the document, a time-shifted
   attack where an attacker is able to modify the content of a Map-Reply
   message but then needs to move off-path could also create redirection
   attacks.  The nonce only allows a xTR to verify that a Map-Reply
   responds to a previously sent Map-Request message.  The LISP Working
   Group should explore solutions that allow to verify the validity and
   integrity of bindings between EID-Prefixes and their RLOCS (e.g.,
   [I-D.saucez-lisp-mapping-security] and [I-D.maino-lisp-sec]).  Having
   such kind of mechanism would allow ITRs to ignore non-verified
   mappings, thus increasing security.

   LISP Working Group should consider developing secure mechanisms to
   allow an ETR to indicate to an ITR that it does not serve a
   particular EID or block of EIDs in order to mitigate the flooding
   attacks.

   Finally, there is also the risk of Denial of Service attack against
   the EID-to-RLOC Cache.  We have discussed these attacks when
   considering external attackers with, e.g., the gleaning mechanism and
   in Section 6.2.  If an ITR has a limited EID-to-RLOC Cache, a
   malicious or compromised host residing in the site that it serves
   could generate packets to random destinations to force the ITR to
   issue a large number of Map-Requests whose answers could fill its
   cache.  Faced with such misbehaving hosts, LISP ITR should be able to
   limit the percent of Map-Requests that it sends for a given source
   EID.


13.  Document Status and Plans

   In this document, we have analyzed some of the security threats that
   affect the Locator/Identifier Separation Protocol (LISP).  We have
   focused our analysis on unicast traffic and considered both the LISP
   data and control planes, and provided some recommendations to improve
   the security of LISP.




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   Revisions of this document will document the security threats of
   other parts of the LISP architecture, including but not limited to:

   o  LISP Multicast ([I-D.ietf-lisp-multicast]).


14.  IANA Considerations

   This document makes no request to IANA.


15.  Security Considerations

   Security considerations are the core of this document and do not need
   to be further discussed in this section.


16.  Acknowledgments

   The flooding attack and the reference environment were first
   described in Marcelo Bagnulo's draft [I-D.bagnulo-lisp-threat].

   This work has been partially supported by the INFSO-ICT-216372
   TRILOGY Project (www.trilogy-project.org).


17.  References

17.1.  Normative References

   [I-D.ietf-lisp]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-14 (work in progress), June 2011.

   [I-D.ietf-lisp-alt]
              Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-07
              (work in progress), June 2011.

   [I-D.ietf-lisp-interworking]
              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-02 (work in progress),
              June 2011.

   [I-D.ietf-lisp-map-versioning]
              Iannone, L., Saucez, D., and O. Bonaventure, "LISP Map-



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              Versioning", draft-ietf-lisp-map-versioning-01 (work in
              progress), March 2011.

   [I-D.ietf-lisp-ms]
              Fuller, V. and D. Farinacci, "LISP Map Server",
              draft-ietf-lisp-ms-09 (work in progress), June 2011.

   [I-D.ietf-lisp-multicast]
              Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
              "LISP for Multicast Environments",
              draft-ietf-lisp-multicast-06 (work in progress),
              June 2011.

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

17.2.  Informative References

   [Chu]      Jerry Chu, H., "Tuning TCP Parameters for the 21st
              Century",  75th IETF, Stockholm, July 2009,
              <http://tools.ietf.org/wg/savi/>.

   [I-D.bagnulo-lisp-threat]
              Bagnulo, M., "Preliminary LISP Threat Analysis",
              draft-bagnulo-lisp-threat-01 (work in progress),
              July 2007.

   [I-D.ietf-sidr-arch]
              Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", draft-ietf-sidr-arch-13 (work in
              progress), May 2011.

   [I-D.ietf-tcpm-tcp-security]
              Gont, F., "Security Assessment of the Transmission Control
              Protocol (TCP)", draft-ietf-tcpm-tcp-security-02 (work in
              progress), January 2011.

   [I-D.lear-lisp-nerd]
              Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
              draft-lear-lisp-nerd-08 (work in progress), March 2010.

   [I-D.maino-lisp-sec]
              Maino, F., Ermagan, V., Cabellos-Aparicio, A., Saucez, D.,
              and O. Bonaventure, "LISP-Security (LISP-SEC)",
              draft-maino-lisp-sec-00 (work in progress), March 2011.

   [I-D.meyer-lisp-cons]
              Brim, S., "LISP-CONS: A Content distribution Overlay



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              Network Service for LISP", draft-meyer-lisp-cons-04 (work
              in progress), April 2008.

   [I-D.saucez-lisp-mapping-security]
              Saucez, D. and O. Bonaventure, "Securing LISP Mapping
              replies", draft-saucez-lisp-mapping-security-00 (work in
              progress), February 2011.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5386]  Williams, N. and M. Richardson, "Better-Than-Nothing
              Security: An Unauthenticated Mode of IPsec", RFC 5386,
              November 2008.

   [SAVI]     IETF, "Source Address Validation Improvements Working
              Group", <http://tools.ietf.org/wg/savi/>.

   [Saucez09]
              Saucez, D. and L. Iannone, "How to mitigate the effect of
              scans on mapping systems",  Submitted to the Trilogy
              Summer School on Future Internet.


Appendix A.  Document Change Log

   o  Version 00 Posted July 2011.

      *  Added discussion on LISP-MS in Section 11.

      *  Added discussion on Instance ID in Section 6.4.

      *  Editorial polishing of the whole document.

      *  Added "Change Log" appendix to keep track of main changes.

      *  Renamed "draft-saucez-lisp-security-03.txt.











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Authors' Addresses

   Damien Saucez
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain la Neuve
   Belgium

   Email: damien.saucez@uclouvain.be


   Luigi Iannone
   Deutsche Telekom Laboratories AG
   Ernst-Reuter Platz 7
   Berlin
   Germany

   Email: luigi@net.t-labs.tu-berlin.de


   Olivier Bonaventure
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain la Neuve
   Belgium

   Email: olivier.bonaventure@uclouvain.be
























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