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Network Working Group                                       D. Farinacci
Internet-Draft                                                  D. Lewis
Intended status: Informational                                  D. Meyer
Expires: April 26, 2012                                    cisco Systems
                                                                C. White
                                                  Logical Elegance, LLC.
                                                        October 24, 2011

                            LISP Mobile Node


   This document describes how a lightweight version of LISP's ITR/ETR
   functionality can be used to provide seamless mobility to a mobile
   node.  The LISP Mobile Node design described in this document uses
   standard LISP functionality to provide scalable mobility for LISP
   mobile nodes.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 April 26, 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
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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
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  4
   3.  Design Overview  . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Design Requirements  . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  User Requirements  . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Network Requirements . . . . . . . . . . . . . . . . . . .  7
   5.  LISP Mobile Node Operation . . . . . . . . . . . . . . . . . .  7
     5.1.  Addressing Architecture  . . . . . . . . . . . . . . . . .  8
     5.2.  Control Plane Operation  . . . . . . . . . . . . . . . . .  8
     5.3.  Data Plane Operation . . . . . . . . . . . . . . . . . . .  9
   6.  Updating Remote Caches . . . . . . . . . . . . . . . . . . . . 10
   7.  Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  LISP Mobile Node to a Stationary Node in a LISP Site . . . 11
       7.1.1.  Handling Unidirectional Traffic  . . . . . . . . . . . 11
     7.2.  LISP Mobile Node to a Non-LISP Stationary Node . . . . . . 12
     7.3.  LISP Mobile Node to LISP Mobile Node . . . . . . . . . . . 12
       7.3.1.  One Mobile Node is Roaming . . . . . . . . . . . . . . 12
     7.4.  Non-LISP Site to a LISP Mobile Node  . . . . . . . . . . . 13
     7.5.  LISP Site to LISP Mobile Node  . . . . . . . . . . . . . . 13
   8.  Multicast and Mobility . . . . . . . . . . . . . . . . . . . . 14
   9.  RLOC Considerations  . . . . . . . . . . . . . . . . . . . . . 15
     9.1.  Mobile Node's RLOC is an EID . . . . . . . . . . . . . . . 15
   10. Mobility Example . . . . . . . . . . . . . . . . . . . . . . . 17
     10.1. Provisioning . . . . . . . . . . . . . . . . . . . . . . . 17
     10.2. Registration . . . . . . . . . . . . . . . . . . . . . . . 17
   11. LISP Implementation in a Mobile Node . . . . . . . . . . . . . 18
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
     12.1. Proxy ETR Hijacking  . . . . . . . . . . . . . . . . . . . 19
     12.2. LISP Mobile Node using an EID as its RLOC  . . . . . . . . 20
   13. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   14. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     15.2. Informative References . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21

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1.  Introduction

   The Locator/ID Separation Protocol (LISP) [LISP] specifies a design
   and mechanism for replacing the addresses currently used in the
   Internet with two separate name spaces: Endpoint Identifiers (EIDs),
   used within sites, and Routing Locators (RLOCs), used by the transit
   networks that make up the Internet infrastructure.  To achieve this
   separation, LISP defines protocol mechanisms for mapping from EIDs to
   RLOCs.  The mapping infrastructure is comprised of LISP Map-Servers
   and Map-Resolvers [LISP-MS] and is tied together with LISP+ALT

   This document specifies the behavior of a new LISP network element:
   the LISP Mobile Node.  The LISP Mobile Node implements a subset of
   the standard Ingress Tunnel Router and Egress Tunnel Router
   functionality [LISP].  Design goals for the LISP mobility design

   o  Allowing TCP connections to stay alive while roaming.

   o  Allowing the mobile node to communicate with other mobile nodes
      while either or both are roaming.

   o  Allowing the mobile node to multi-home (i.e., use multiple
      interfaces concurrently).

   o  Allowing the mobile node to be a server.  That is, any mobile node
      or stationary node can find and connect to a mobile node as a

   o  Providing shortest path bidirectional data paths between a mobile
      node and any other stationary or mobile node.

   o  Not requiring fine-grained routes in the core network to support

   o  Not requiring a home-agent, foreign agent or other data plane
      network elements to support mobility.  Note since the LISP mobile
      node design does not require these data plane elements, there is
      no triangle routing of data packets as is found in Mobile IP

   o  Not requiring new IPv6 extension headers to avoid triangle routing

   The LISP Mobile Node design requires the use of the LISP Map-Server
   [LISP-ALT] and LISP Interworking [LISP-INTERWORK] technology to allow
   a LISP mobile node to roam and to be discovered in an efficient and

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   scalable manner.  The use of Map-Server technology is discussed
   further in Section 5.

   The protocol mechanisms described in this document apply those cases
   in which a node's IP address changes frequently.  For example, when a
   mobile node roams, it is typically assigned a new IP address.
   Similarly, a broadband subscriber may have its address change
   frequently; as such, a broadband subscriber can use the LISP Mobile
   Node mechanisms defined in this specification.

   The remainder of this document is organized as follows: Section 2
   defines the terms used in this document.  Section 3 provides a
   overview of salient features of the LISP Mobile Node design, and
   Section 4 describes design requirements for a LISP Mobile Node.
   Section 5 provides the detail of LISP Mobile Node data and control
   plane operation, and Section 6 discusses options for updating remote
   caches in the presence of unidirectional traffic flows.  Section 7
   specifies how the LISP Mobile Node protocol operates.  Section 8
   specifies multicast operation for LISP mobile nodes.  Section 9 and
   Section 11 outline other considerations for the LISP-MN design and
   implementation.  Finally, Section 12 outlines the security
   considerations for a LISP mobile node.

2.  Definition of Terms

   This section defines the terms used in this document.

   Stationary Node (SN):  A non-mobile node who's IP address changes
      infrequently.  That is, its IP address does not change as
      frequently as a fast roaming mobile hand-set or a broadband
      connection and therefore the EID to RLOC mapping is relatively

   Endpoint ID (EID):  This is the traditional LISP EID [LISP], and is
      the address that a LISP mobile node uses as its address for
      transport connections.  A LISP mobile node never changes its EID,
      which is typically a /32 or /128 prefix and is assigned to a
      loopback interface.  Note that the mobile node can have multiple
      EIDs, and these EIDs can be from different address families.

   Routing Locator (RLOC):  This is the traditional LISP RLOC, and is in
      general a routable address that can be used to reach a mobile
      node.  Note that there are cases in which an mobile node may
      receive an address that it thinks is an RLOC (perhaps via DHCP)
      which is either an EID or an RFC 1918 address [RFC1918].  This
      could happen if, for example, if the mobile node roams into a LISP
      domain or a domain behind a Network Address Translator (NAT)).

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   Ingress Tunnel Router (ITR):  An ITR is a router that accepts an IP
      packet with a single IP header (more precisely, an IP packet that
      does not contain a LISP header).  The router treats this "inner"
      IP destination address as an EID and performs an EID-to-RLOC
      mapping lookup.  The router then prepends an "outer" IP header
      with one of its globally routable RLOCs in the source address
      field and the result of the mapping lookup in the destination
      address field.  Note that this destination RLOC may be an
      intermediate, proxy device that has better knowledge of the EID-
      to-RLOC mapping closer to the destination EID.  In general, an ITR
      receives IP packets from site end-systems on one side and sends
      LISP-encapsulated IP packets toward the Internet on the other
      side.  A LISP mobile node, however, when acting as an ITR LISP
      encapsulates all packet that it originates.

   Egress Tunnel Router (ETR):  An ETR is a router that accepts an IP
      packet where the destination address in the "outer" IP header is
      one of its own RLOCs.  The router strips the "outer" header and
      forwards the packet based on the next IP header found.  In
      general, an ETR receives LISP-encapsulated IP packets from the
      Internet on one side and sends decapsulated IP packets to site
      end-systems on the other side.  A LISP mobile node, when acting as
      an ETR, decapsulates packets that are then typically processed by
      the mobile node.

   Proxy Ingress Tunnel Router (PITR):  PITRs are used to provide
      interconnectivity between sites that use LISP EIDs and those that
      do not.  They act as a gateway between the Legacy Internet and the
      LISP enabled Network.  A given PITR advertises one or more highly
      aggregated EID prefixes into the public Internet and acts as the
      ITR for traffic received from the public Internet.  Proxy Ingress
      Tunnel Routers are described in [LISP-INTERWORK].

   Proxy Egress Tunnel Router (PETR):  An infrastructure element used to
      decapsulate packets sent from mobile nodes to non-LISP sites.
      Proxy Egress Tunnel Routers are described in [LISP-INTERWORK].

   LISP Mobile Node (LISP-MN):  A LISP capable fast roaming mobile hand-

   Map-cache:  A data structure which contains an EID-prefix, its
      associated RLOCs, and the associated policy.  Map-caches are
      typically found in ITRs and PITRs.

   Negative Map-Reply:  A Negative Map-Reply is a Map-Reply that
      contains a coarsely aggregated non-LISP prefix.  Negative Map-
      Replies are typically generated by Map-Resolvers, and are used to
      inform an ITR (mobile or stationary) that a site is not a LISP

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      site.  A LISP mobile node encapsulate packets to destinations
      covered by the negative Map-Reply are encapsulated to a PETR.

   Roaming Event:  A Roaming Event occurs when there is a change in a
      LISP mobile node's RLOC set.

3.  Design Overview

   The LISP-MN design described in this document uses the Map-Server/
   Map-Resolver service interface in conjunction with a light-weight
   ITR/ETR implementation in the LISP-MN to provide scalable fast
   mobility.  The LISP-MN control-plane uses a Map-Server as an anchor
   point, which provides control-plane scalability.  In addition, the
   LISP-MN data-plane takes advantage of shortest path routing and
   therefore does not increase packet delivery latency.

4.  Design Requirements

   This section outlines the design requirements for a LISP-MN, and is
   divided into User Requirements (Section 4.1) and Network Requirements
   (Section 4.2).

4.1.  User Requirements

   This section describes the user-level functionality provided by a

   Transport Connection Survivability:  The LISP-MN design must allow a
      LISP-MN to roam while keeping transport connections alive.

   Simultaneous Roaming:  The LISP-MN design must allow a LISP-MN to
      talk to another LISP-MN while both are roaming.

   Multihoming:  The LISP-MN design must allow for simultaneous use of
      multiple Internet connections by a LISP-MN.  In addition, the
      design must allow for the LISP mobile node to specify ingress
      traffic engineering policies as documented in [LISP].  That is,
      the LISP-MN must be able to specify both active/active and active/
      passive policies for ingress traffic.

   Shortest Path Data Plane:  The LISP-MN design must allow for shortest
      path bidirectional traffic between a LISP-MN and a stationary
      node, and between a LISP-MN and another LISP-MN (i.e., without
      triangle routing in the data path).  This provides a low-latency
      data path between the LISP-MN and the nodes that it is
      communicating with.

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4.2.  Network Requirements

   This section describes the network functionality that the LISP-MN
   design provides to a LISP-MN.

   Routing System Scalability:  The LISP-MN design must not require
      injection of fine-grained routes into the core network.

   Mapping System Scalability:  The LISP-MN design must not require
      additional state in the mapping system.  In particular, any
      mapping state required to support LISP mobility must BE confined
      to the LISP-MN's Map-Server and the ITRs which are talking to the

   Component Reuse:  The LISP-MN design must use existing LISP
      infrastructure components.  These include map server, map
      resolver, and interworking infrastructure components.

   Home Agent/Foreign Agent:  The LISP-MN design must not require the
      use of home-agent or foreign-agent infrastructure components

   Readdressing:  The LISP-MN design must not require TCP connections to
      be reset when the mobile node roams.  In particular, since the IP
      address associated with a transport connection will not change as
      the mobile node roams, TCP connections will not reset.

5.  LISP Mobile Node Operation

   The LISP-MN design is built from three existing LISP components: A
   lightweight LISP implementation that runs in an LISP-MN, and the
   existing Map-Server [LISP-MS] and Interworking [LISP-INTERWORK]
   infrastructures.  A LISP mobile node typically sends and receives
   LISP encapsulated packets (exceptions include management protocols
   such as DHCP).

   The LISP-MN design makes a single mobile node look like a LISP site
   as described in in [LISP] by implementing ITR and ETR functionality.
   Note that one subtle difference between standard ITR behavior and
   LISP-MN is that the LISP-MN encapsulates all non-local, non-LISP site
   destined outgoing packets to a PETR.

   When a LISP-MN roams onto a new network, it receives a new RLOC.
   Since the LISP-MN is the authoritative ETR for its EID-prefix, it
   must Map-Register it's updated RLOC set.  New sessions can be
   established as soon as the registration process completes.  Sessions
   that are encapsulating to RLOCs that did not change during the

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   roaming event are not affected by the roaming event (or subsequent
   mapping update).  However, the LISP-MN must update the ITRs and PITRs
   that have cached a previous mapping.  It does this using the
   techniques described in Section 6.

5.1.  Addressing Architecture

   A LISP-MN is typically provisioned with one or more EIDs that it uses
   for all transport connections.  LISP-MN EIDs are provisioned from
   blocks reserved from mobile nodes much the way mobile phone numbers
   are provisioned today (such that they do not overlap with the EID
   space of any enterprise).  These EIDs can be either IPv4 or IPv6
   addresses.  For example, one EID might be for a public network while
   another might be for a private network; in this case the "public" EID
   will be associated with RLOCs from the public Internet, while the
   "private" EID will be associated with private RLOCs.  It is
   anticipated that these EIDs will change infrequently if at all, since
   the assignment of a LISP-MN's EID is envisioned to be a subscription
   time event.  The key point here is that the relatively fixed EID
   allows the LISP-MN's transport connections to survive roaming events.
   In particular, while the LISP-MN's EIDs are fixed during roaming
   events, the LISP-MN's RLOC set will change.  The RLOC set may be
   comprised of both IPv4 or IPv6 addresses.

   A LISP-MN is also provisioned with the address of a Map-Server and a
   corresponding authentication key.  Like the LISP-MN's EID, both the
   Map-Server address and authentication key change very infrequently
   (again, these are anticipated to be subscription time parameters).
   Since the LISP LISP-MN's Map-Server is configured to advertise an
   aggregated EID-prefix that covers the LISP-MN's EID, changes to the
   LISP-MN's mapping are not propagated further into the mapping system
   [LISP-ALT].  It is this property that provides for scalable fast

   A LISP-MN is also be provisioned with the address of a Map-Resolver.
   A LISP-MN may also learn the address of a Map-Resolver though a
   dynamic protocol such as DHCP [RFC2131].

   Finally, note that if, for some reason, a LISP-MN's EID is re-
   provisioned, the LISP-MN's Map-Server address may also have to change
   in order to keep LISP-MN's EID within the aggregate advertised by the
   Map-Server (this is discussed in greater detail in Section 5.2).

5.2.  Control Plane Operation

   A roaming event occurs when the LISP-MN receives a new RLOC.  Because
   the new address is a new RLOC from the LISP-MN's perspective, it must
   update its EID-to-RLOC mapping with its Map-Server; it does this

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   using the Map-Register mechanism described in [LISP].

   A LISP-MN may want the Map-Server to respond on its behalf for a
   variety of reasons, including minimizing control traffic on radio
   links and minimizing battery utilization.  A LISP-MN may instruct its
   Map-Server to proxy respond to Map-Requests by setting the Proxy-Map-
   Reply bit in the Map-Register message [LISP].  In this case the Map-
   Server responds with a non-authoritative Map-Reply so that an ITR or
   PITR will know that the ETR didn't directly respond.  A Map-Server
   will proxy reply only for "registered" EID-prefixes using the
   registered EID-prefix mask-length in proxy replies.

   Because the LISP-MN's Map-Server is pre-configured to advertise an
   aggregate covering the LISP-MN's EID prefix, the database mapping
   change associated with the roaming event is confined to the Map-
   Server and those ITRs and PITRs that may have cached the previous

5.3.  Data Plane Operation

   A key feature of LISP-MN control-plane design is the use of the Map-
   Server as an anchor point; this allows control of the scope to which
   changes to the mapping system must be propagated during roaming

   On the other hand, the LISP-MN data-plane design does not rely on
   additional LISP infrastructure for communication between LISP nodes
   (mobile or stationary).  Data packets take the shortest path to and
   from the LISP-MN to other LISP nodes; as noted above, low latency
   shortest paths in the data-plane is an important goal for the LISP-MN
   design (and is important for delay-sensitive applications like gaming
   and voice-over-IP).  Note that a LISP-MN will need additional
   interworking infrastructure when talking to non-LISP sites
   [LISP-INTERWORK]; this is consistent with the design of any host at a
   LISP site which talks to a host at a non-LISP site.

   In general, the LISP-MN data-plane operates in the same manner as the
   standard LISP data-plane with one exception: packets generated by a
   LISP-MN which are not destined for the mapping system (i.e., those
   sent to destination UDP port 4342) or the local network are LISP
   encapsulated.  Because data packets are always encapsulated to a
   RLOC, packets travel on the shortest path from LISP-MN to another
   LISP stationary or LISP-MN.  When the LISP mobile node is sending
   packets to a stationary or LISP-MN in a non-LISP site, it sends LISP-
   encapsulated packets to a PETR which then decapsulates the packet and
   forwards it to its destination.

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6.  Updating Remote Caches

   A LISP-MN has five mechanisms it can use to cause the mappings cached
   in remote ITRs and PITRs to be refreshed:

   Map Versioning:  If Map Versioning [LISP-VERSIONING] is used, an ETR
      can detect if an ITR is using the most recent database mapping.
      In particular, when mobile node's ETR decapsulates a packet and
      detects the Destination Map-Version Number is less than the
      current version for its mapping, in invokes the SMR procedure
      described in [LISP].  In general, SMRs are used to fix the out of
      sync mapping while Map-Versioning is used to detect they are out
      of sync.  [LISP-VERSIONING] provides additional details of the Map
      Versioning process.

   Data Driven SMRs:  An ETR may elect to send SMRs to those sites it
      has been receiving encapsulated packets from.  This will occur
      when an ITR is sending to an old RLOC (for which there is one-to-
      one mapping between EID-to-RLOC) and the ETR may not have had a
      chance to send an SMR the ITR.

   Setting Small TTL on Map Replies:  The ETR (or Map Server) may set a
      small Time to Live (TTL) on its mappings when responding to Map
      Requests.  The TTL value should be chosen such that changes in
      mappings can be detected while minimizing control traffic.  In
      this case the ITR is a SN and the ETR is the MN.

   Piggybacking Mapping Data:  If an ITR and ETR are co-located, an ITR
      may elect to send Map-Requests with piggybacked mapping data to
      those sites in its map cache or to which it has recently
      encapsulated data in order to inform the remote ITRs and PITRs of
      the change.

   Temporary PITR Caching:  The ETR can keep a cache of PITRs that have
      sent Map-Requests to it.  The cache contains the RLOCs of the
      PITRs so later when the locator-set of a LISP-MN changes, SMR
      messages can be sent to all RLOCs in the PITR cache.  This is an
      example of a control-plane driven SMR procedure.

7.  Protocol Operation

   There are five distinct connectivity cases considered by the LISP-MN
   design.  The five mobility cases are:

      LISP Mobile Node to a Stationary Node in a LISP Site.

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      LISP Mobile Node to a Non-LISP Site.

      LISP Mobile Node to a LISP Mobile Node.

      Non-LISP Site to a LISP Mobile Node.

      LISP Site to a LISP Mobile Node.

   The remainder of this section covers these cases in detail.

7.1.  LISP Mobile Node to a Stationary Node in a LISP Site

   After a roaming event, a LISP-MN must immediately register its new
   EID-to-RLOC mapping with its configured Map-Server(s).  This allows
   LISP sites sending Map-Requests to the LISP-MN to receive the current
   mapping.  In addition, remote ITRs and PITRs may have cached mappings
   that are no longer valid.  These ITRs and PITRs must be informed that
   the mapping has changed.  See Section 6 for a discussion of methods
   for updating remote caches.

7.1.1.  Handling Unidirectional Traffic

   A problem may arise when traffic is flowing unidirectionally between
   LISP sites.  This can arise in communication flows between PITRs and
   LISP sites or when a site's ITRs and ETRs are not co-located.  In
   these cases, data-plane techniques such as Map-Versioning and Data-
   Driven SMRs can't be used to update the remote caches.

   For example, consider the unidirectional packet flow case depicted in
   Figure 1.  In this case X is a non-LISP enabled SN (i.e., connected
   to the Internet) and Y is a LISP MN.  Data traffic from X to Y will
   flow through a PITR.  When Y changes its mapping (for example, during
   a mobility event), the PITR must update its mapping for Y. However,
   since data traffic from Y to X is unidirectional and does not flow
   though the PITR, it can not rely data traffic from Y to X to signal a
   mapping change at Y. In this case, the Y must use one or more of the
   techniques described in Section 6 to update the PITR's cache.  Note
   that if Y has only one RLOC, then the PITR has to know when to send a
   Map-Request based on its existing state; thus it can only rely on the
   TTL on the existing mapping.

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      |                                           |
      |                                           | DP
      v   DP              DP            MQ        |
      X -----> Internet -----> PITR ------------> Y
                                ^      LEDP       |
                                |                 |

     DP:   Data Packet
     LEDP: LISP Encapsulated Data Packet
     MQ:   Map Request
     MR:   Map Reply

                   Figure 1: Unidirectional Packet Flow

7.2.  LISP Mobile Node to a Non-LISP Stationary Node

   LISP-MNs use the LISP Interworking infrastructure (specifically a
   PETR) to reach non-LISP sites.  In general, the PETR will be co-
   located with the LISP-MN's Map-Server.  This ensures that the LISP
   packets being decapsulated are from sources that have Map-Registered
   to the Map-Server.  Note that when a LISP-MN roams it continues to
   uses its configured PETR and Map-Server which can have the effect of
   adding stretch to packets sent from a LISP-MN to a non-LISP

7.3.  LISP Mobile Node to LISP Mobile Node

   LISP-MN to LISP-MN communication is an instance of LISP-to-LISP
   communication with three sub-cases:

   o  Both LISP-MNs are stationary (Section 7.1).

   o  Only one LISP-MN is roaming (Section 7.3.1).

   o  Both LISP-MNs are roaming.  The case is analogous to the case
      described in Section 7.3.1.

7.3.1.  One Mobile Node is Roaming

   In this case, the roaming LISP-MN can find the stationary LISP-MN by
   sending Map-Request for its EID-prefix.  After receiving a Map-Reply,
   the roaming LISP-MN can encapsulate data packets directly to the non-
   roaming LISP-MN node.

   The roaming LISP-MN, on the other hand, must update its Map-Server

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   with the new mapping data as described in Section 7.1.  It should
   also use the cache management techniques described in Section 6 to
   provide for timely updates of remote caches.  Once the roaming
   LISP-MN has updated its Map-Server, the non-roaming LISP-MN can
   retrieve the new mapping data (if it hasn't already received an
   updated mapping via one of the mechanisms described in Section 6) and
   the stationary LISP-MN can encapsulate data directly to the roaming

7.4.  Non-LISP Site to a LISP Mobile Node

   When a stationary ITR is talking to a non-LISP site, it may forward
   packets natively (unencapsulated) to the non-LISP site.  This will
   occur when the ITR has received a negative Map Reply for a prefix
   covering the non-LISP site's address with the Natively-Forward action
   bit set [LISP].  As a result, packets may be natively forwarded to
   non-LISP sites by an ITR (the return path will through a PITR,
   however, since the packet flow will be non-LISP site to LISP site).

   A LISP-MN behaves differently when talking to non-LISP sites.  In
   particular, the LISP-MN always encapsulates packets to a PETR.  The
   PETR then decapsulates the packet and forwards it natively to its
   destination.  As in the stationary case, packets from the non-LISP
   site host return to the LISP-MN through a PITR.  Since traffic
   forwarded through a PITR is unidirectional, a LISP-MN should use the
   cache management techniques described in Section 7.1.1.

7.5.  LISP Site to LISP Mobile Node

   When a LISP-MN roams onto a new network, it needs to update the
   caches in any ITRs that might have stale mappings.  This is analogous
   to the case in that a stationary LISP site is renumbered; in that
   case ITRs that have cached the old mapping must be updated.  This is
   done using the techniques described in Section 6.

   When a LISP router in a stationary site is performing both ITR and
   ETR functions, a LISP-MN can update the stationary site's map-caches
   using techniques described in Section 6.  However, when the LISP
   router in the stationary site is performing is only ITR
   functionality, these techniques can not be used because the ITR is
   not receiving data traffic from the LISP-MN.  In this case, the
   LISP-MN should use the technique described in Section 7.1.1.  In
   particular, a LISP-MN should set the TTL on the mappings in its Map-
   Replies to be in 1-2 minute range.

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8.  Multicast and Mobility

   Since a LISP-MN performs both ITR and ETR functionality, it should
   also perform a lightweight version of multicast ITR/ETR functionality
   described in [MLISP].  When a LISP-MN originates a multicast packet,
   it will encapsulate the packet with a multicast header, where the
   source address in the outer header is one of it's RLOC addresses and
   the destination address in the outer header is the group address from
   the inner header.  The interfaces in which the encapsulated packet is
   sent on is discussed below.

   To not require PIM functionality in the LISP-MN as documented in
   [MLISP], the LISP-MN resorts to using encapsulated IGMP for joining
   groups and for determining which interfaces are used for packet
   origination.  When a LISP-MN joins a group, it obtains the map-cache
   entry for the (S-EID,G) it is joining.  It then builds a IGMP report
   encoding (S-EID,G) and then LISP encapsulates it with UDP port 4341.
   It selects an RLOC from the map-cache entry to send the encapsulated
   IGMP Report.

   When other LISP-MNs are joining an (S-EID,G) entry where the S-EID is
   for a LISP-MN, the encapsulated IGMP Report will be received by the
   LISP-MN multicast source.  The LISP-MN multicast source will remember
   the interfaces the encapsulated IGMP Report is received on and build
   an outgoing interface list for it's own (S-EID,G) entry.  If the list
   is greater than one, then the LISP-MN is doing replication on the
   source-based tree for which it is the root.

   When other LISP routers are joining (S-EID,G), they are instructed to
   send PIM encapsulated Join-Prune messages.  However, to keep the
   LISP-MN as simple as possible, the LISP-MN will not be able to
   process encapsulated PIM Join-Prune messages.  Because the map-cache
   entry will have a MN-bit indicating the entry is for a LISP-MN, the
   LISP router will send IGMP encapsulated IGMP Reports instead.

   When the LISP-MN is sending a multicast packet, it can operate in two
   modes, multicast-origination-mode or unicast-origination-mode.  When
   in multicast-origination-mode, the LISP-MN multicast-source can
   encapsulate a multicast packet in another multicast packet, as
   described above.  When in unicast-origination-mode, the LISP-MN
   multicast source encapsulates the multicast packet into a unicast
   packet and sends a packet to each encapsulated IGMP Report sender.

   These modes are provided depending on whether or not the mobile
   node's network it is currently connected can support IP multicast.

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9.  RLOC Considerations

   This section documents cases where the expected operation of the
   LISP-MN design may require special treatment.

9.1.  Mobile Node's RLOC is an EID

   When a LISP-MN roams into a LISP site, the "RLOC" it is assigned may
   be an address taken from the site's EID-prefix.  In this case, the
   LISP-MN will Map-Register a mapping from its statically assigned EID
   to the "RLOC" it received from the site.  This scenario creates
   another level of indirection: the mapping from the LISP-MN's EID to a
   site assigned EID.  The mapping from the LISP-MN's EID to the site
   assigned EID allow the LISP-MN to be reached by sending packets using
   the mapping for the EID; packets are delivered to site's EIDs use the
   same LISP infrastructure that all LISP hosts use to reach the site.

   A packet egressing a LISP site destined for a LISP-MN that resides in
   a LISP site will have three headers: an inner header that is built by
   the host and is used by transport connections, a middle header that
   is built by the site's ITR and is used by the destination's ETR to
   find the current topological location of the LISP-MN, and an outer
   header (also built by the site's ITR) that is used to forward packets
   between the sites.

   Consider a site A with EID-prefix and RLOC A and a site B
   with EID-prefix and RLOC B. Suppose that a host S in site A
   with EID wants to talk to a LISP LISP-MN MN that has
   registered a mapping from EID to "RLOC" (where allocated from site B's EID prefix, in this case).
   This situation is depicted in Figure 2.

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     EID-prefix                           EID-prefix
     S has EID                              MN has EID
                                                    MN has RLOC
      --------------                                   --------------
    /                \       ---------------         /                \
   |          ITR-A'  |    /                 \      |  ETR-B'          |
   |                  |   |                   |     |                  |
   |   S              |   |     Internet      |     |              MN  |
   |    \             |   |                   |     |             ^    |
   |     \            |   |                   |     |            /     |
   |      --> ITR-A   |    \                 /      |  ETR-B ----      |
    \                /       ---------------         \                /
      --------------                                   --------------
       |       |  |                                       ^     ^  ^
       |       |  |                                       |     |  |
       |       |  |         outer-header: A -> B          |     |  |
       |       |  +---------------------------------------+     |  |
       |       |   RLOCs used to find which site MN resides     |  |
       |       |                                                |  |
       |       |                                                |  |
       |       |            middle-header: A ->         |  |
       |       +------------------------------------------------+  |
       |         RLOCs used to find topological location of MN     |
       |                                                           |
       |                                                           |
       |               inner-header: ->          |
                          EIDs used for TCP connection

              Figure 2: Mobile Node Roaming into a LISP Site

   In this case, the inner header is used for transport connections, the
   middle header is used to find topological location of the LISP-MN
   (the LISP-MN Map-Registers the mapping -> when it
   roams into site B), and the outer header is used to move packets
   between sites (A and B in Figure 2).

   In summary, when a LISP-MN roams into a LISP site and receives a new
   address (e.g., via DHCP) that is part of the site's EID space, the
   following sequence occurs:

   1.  The LISP-MN in the LISP site (call it Inside) registers its new
       RLOC (which is actually part of the sites EID prefix) to its map-
       server.  Call its permanent EID E and the EID it DHCPs D. So it
       registers a mapping that looks like E->D.

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   2.  The MN which is outside (call it Outside) sends a map request for
       inside's EID (E) and receives D (plus its policy).  Outside
       realizes that D is an EID and sends a map request for D. This
       will return the site's RLOCs (by its ETR).  Call this R.

   3.  Outside then double encapsulates the outbound packet with the
       inner destination being D and the outer destination being R.

   4.  The packet then finds its way to R, which strips the outer header
       and the packet is routed to D in the domain to Inside.  Inside
       decapsulates the packet to serve the inner header to the

   Note that both D and R could be returned to Inside in one query, so
   as not to incur the additional RTT.

10.  Mobility Example

   This section provides an example of how the LISP-MN is integrated
   into the base LISP Design [LISP].

10.1.  Provisioning

   The LISP-MN needs to be configured with the following information:

      An EID, assigned to its loopback address

      A key for map-registration

      An IP address of a Map-Resolver (this could be learned

      An IP address of its Map-Server and Proxy ETR

10.2.  Registration

   After a LISP roams to a new network, it must immediately register its
   new mapping this new RLOC (and associated priority/weight data) with
   its Map-Server.

   The LISP-MN may chose to set the 'proxy' bit in the map-register to
   indicate that it desires its Map-Server to answer map-requests on its

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11.   LISP Implementation in a Mobile Node

   This section will describe a possible approach for developing a
   lightweight LISP-MN implementation.  A LISP-MN will implement a LISP
   sub-layer inside of the IP layer of the protocol stack.  The sub-
   layer resides between the IP layer and the link-layer.

   For outgoing unicast packets, once the header that contains EIDs is
   built and right before an outgoing interface is chosen, a LISP header
   is prepended to the outgoing packet.  The source address is set to
   the local RLOC address (obtained by DHCP perhaps) and the destination
   address is set to the RLOC associated with the destination EID from
   the IP layer.  To obtain the RLOC for the EID, the LISP-MN maintains
   a map-cache for destination sites or destination LISP-MNs to which it
   is currently talking.  The map-cache lookup is performed by doing a
   longest match lookup on the destination address the IP layer put in
   the first IP header.  Once the new header is prepended, a route table
   lookup is performed to find the interface in which to send the packet
   or the default router interface is used to send the packet.

   When the map-cache does not exist for a destination, the mobile node
   may queue or drop the packet while it sends a Map-Request to it's
   configured Map-Resolver.  Once a Map-Reply is returned, the map-cache
   entry stores the EID-to-RLOC state.  If the RLOC state is empty in
   the Map-Reply, the Map-Reply is known as a Negative Map-Reply in
   which case the map-cache entry is created with a single RLOC, the
   RLOC of the configured Map-Server for the LISP-MN.  The Map-Server
   that serves the LISP-MN also acts as a Proxy ETR (PETR) so packets
   can get delivered to hosts in non-LISP sites to which the LISP-MN is

   For incoming unicast packets, the LISP sub-layer simply decapsulates
   the packets and delivers to the IP layer.  The loc-reach-bits can be
   processed by the LISP sub-layer.  Specifically, the source EID from
   the packet is looked up in the map-cache and if the loc-reach-bits
   settings have changed, store the loc-reach-bits from the packet and
   note which RLOCs for the map-cache entry should not be used.

   In terms of the LISP-MN detecting which RLOCs from each stored map-
   cache entry is reachable, it can use any of the Locator Reachability
   Algorithms from [LISP].

   A background task that runs off a timer should be run so the LISP-MN
   can send periodic Map-Register messages to the Map-Server.  The Map-
   Register message should also be triggered when the LISP-MN detects a
   change in IP address for a given interface.  The LISP-MN should send
   Map-Registers to the same Map-Register out each of it's operational
   links.  This will provide for robustness on radio links with which

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   the mobile node is associated.

   A LISP-MN receives a Map-Request when it has Map-Registered to a Map-
   Server with the Proxy-bit set to 0.  This means that the LISP-MN
   wishes to send authoritative Map-Replies for Map-Requests that are
   targeted at the LISP-MN.  If the Proxy-bit is set when the LISP-MN
   registers, then the Map-Server will send non-authoritative Map-
   Replies on behalf of the LISP-MN.  In this case, the Map-Server never
   encapsulates Map-Requests to the LISP-MN.  The LISP-MN can save
   resources by not receiving Map-Requests (note that the LISP-MN will
   receive SMRs which have the same format as Map-Requests).

   To summarize, a LISP sub-layer should implement:

   o  Encapsulating and decapsulating data packets.

   o  Sending and receiving of Map-Request control messages.

   o  Receiving and optionally sending Map-Replies.

   o  Sending Map-Register messages periodically.

   The key point about the LISP sub-layer is that no other components in
   the protocol stack need changing; just the insertion of this sub-
   layer between the IP layer and the interface layer-2 encapsulation/
   decapsulation layer.

12.  Security Considerations

   Security for the LISP-MN design builds upon the security fundamentals
   found in LISP [LISP] for data-plane security and the LISP Map Server
   [LISP-MS] registration security.  Security issues unique to the
   LISP-MN design are considered below.

12.1.  Proxy ETR Hijacking

   The Proxy ETR (or PETR) that a LISP-MN uses as its destination for
   non-LISP traffic must use the security association used by the
   registration process outlined in Section 5.2 and explained in detail
   in the LISP-MS specification [LISP-MS].  These measures prevent third
   party injection of LISP encapsulated traffic into a Proxy ETR.
   Importantly, a PETR must not decapsulate packets from non-registered

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12.2.  LISP Mobile Node using an EID as its RLOC

   For LISP packets to be sent to a LISP-MN which has an EID assigned to
   it as an RLOC as described in Section 9.1), the LISP site must allow
   for incoming and outgoing LISP data packets.  Firewalls and stateless
   packet filtering mechanisms must be configured to allow UDP port 4341
   and UDP port 4342 packets.

13.  Acknowledgments

   Albert Cabellos, Noel Chiappa, Pierre Francois, Michael Menth, Andrew
   Partan, Chris White and John Zwiebel provided insightful comments on
   the mobile node concept and on this document.  A special thanks goes
   to Mary Nickum for her attention to detail and effort in editing
   early versions of this document.

14.  IANA Considerations

   This document creates no new requirements on IANA namespaces

15.  References

15.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

   [RFC3344]  Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

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15.2.  Informative References

   [LISP]     Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-16.txt (work in progress), October 2011.

              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP-ALT)",
              draft-ietf-lisp-alt-09.txt (work in progress),
              September 2011.

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

   [LISP-MS]  Farinacci, D. and V. Fuller, "LISP Map Server",
              draft-ietf-lisp-ms-11.txt (work in progress), August 2011.

              Iannone, L., Saucez, D., and O. Bonaventure, "LISP Mapping
              Versioning", draft-ietf-lisp-map-versioning-05.txt (work
              in progress), October 2011.

   [MLISP]    Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
              "LISP for Multicast Environments",
              draft-ietf-lisp-multicast-11.txt (work in progress),
              October 2011.

Authors' Addresses

   Dino Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134

   Email: dino@cisco.com

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   Darrel Lewis
   cisco Systems
   Tasman Drive
   San Jose, CA  95134

   Email: darlewis@cisco.com

   David Meyer
   cisco Systems
   Tasman Drive
   San Jose, CA  95134

   Email: dmm@1-4-5.net

   Chris White
   Logical Elegance, LLC.
   San Jose, CA  95134

   Email: chris@logicalelegance.com

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