Network Working Group                                          V. Fuller
Internet-Draft                                              D. Farinacci
Intended status: Experimental                              cisco Systems
Expires: July 14, 2012                                  January 11, 2012

                       LISP Map Server Interface


   This draft describes the Maping Service for the Locator Identifier
   Separation Protocol (LISP), implemented by two new types of LISP-
   speaking devices, the LISP Map Resolver and LISP Map Server, that
   provides a simplified "front end" to for one or more Endpoint ID to
   Routing Locator mapping databases.

   By using this service interface and communicating with Map Resolvers
   and Map Servers, LISP Ingress Tunnel Routers and Egress Tunnel
   Routers, are not dependent on the details of mapping database
   systems, which facilitates experimentation with different database
   designs.  Since these devices implement the "edge" of the LISP
   infrastructure, connect directly to LISP-capable Internet end sites,
   and comprise the bulk of LISP-speaking devices, reducing their
   implementation and operational complexity should also reduce the
   overall cost and effort of deploying LISP.

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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   This Internet-Draft will expire on July 14, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  4
   3.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Interactions With Other LISP Components  . . . . . . . . . . .  6
     4.1.  ITR EID-to-RLOC Mapping Resolution . . . . . . . . . . . .  6
     4.2.  EID Prefix Configuration and ETR Registration  . . . . . .  7
     4.3.  Map Server Processing  . . . . . . . . . . . . . . . . . .  8
     4.4.  Map Resolver Processing  . . . . . . . . . . . . . . . . .  9
       4.4.1.  Anycast Map Resolver Operation . . . . . . . . . . . . 10
   5.  Open Issues and Considerations . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   [LISP], the Locator Identifier Separation Protocol, specifies an
   architecture and mechanism for replacing the addresses currently used
   by IP with two separate name spaces: Endpoint IDs (EIDs), used within
   sites, and Routing Locators (RLOCs), used on the transit networks
   that make up the Internet infrastructure.  To achieve this
   separation, LISP defines protocol mechanisms for mapping from EIDs to
   RLOCs.  In addition, LISP assumes the existence of a database to
   store and propagate those mappings globally.  Several such databases
   have been proposed, among them: LISP-CONS [CONS], LISP-NERD, [NERD]
   and LISP+ALT [ALT].

   The LISP Mapping Service defines two new types of LISP-speaking
   devices: the Map Resolver, which accepts Map-Requests from an Ingress
   Tunnel Router (ITR) and "resolves" the EID-to-RLOC mapping using a
   mapping database, and the Map Server, which learns authoritative EID-
   to-RLOC mappings from an Egress Tunnel Router (ETR) and publishes
   them in a database.

   Conceptually, LISP Map Servers share some of the same basic
   configuration and maintenance properties as Domain Name System (DNS)
   [RFC1035] servers; likewise, Map Resolvers are conceptually similar
   to DNS caching resolvers.  With this in mind, this specification
   borrows familiar terminology (resolver and server) from the DNS

   Note that while this document assumes a LISP+ALT database mapping
   infrastructure to illustrate certain aspects of Map Server and Map
   Resolver operation, the Mapping Service interface can (and likely
   will) be used by ITRs and ETRs to access other mapping database
   systems as the LISP infrastructure evolves.

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2.  Definition of Terms

   Map Server:   a network infrastructure component which learns of EID-
      prefix mapping entries from an ETR, via the registration mechanism
      described below, or some other authoritative source if one exists.
      A Map Server publishes these EID-prefixes in a mapping database.

   Map Resolver:   a network infrastructure component which accepts LISP
      Encapsulated Map-Requests, typically from an ITR, determines
      whether or not the destination IP address is part of the EID
      namespace; if it is not, a Negative Map-Reply is returned.
      Otherwise, the Map Resolver finds the appropriate EID-to-RLOC
      mapping by consulting a mapping database system.

   Encapsulated Map-Request:   a LISP Map-Request carried within an
      Encapsulated Control Message, which has an additional LISP header
      prepended.  Sent to UDP destination port 4342.  The "outer"
      addresses are globally-routeable IP addresses, also known as
      RLOCs.  Used by an ITR when sending to a Map Resolver and by a Map
      Server when forwarding a Map-Request to an ETR.

   Negative Map-Reply:   a LISP Map-Reply that contains an empty
      locator-set.  Returned in response to a Map-Request if the
      destination EID does not exist in the mapping database.
      Typically, this means that the "EID" being requested is an IP
      address connected to a non-LISP site.

   Map-Register message:   a LISP message sent by an ETR to a Map Server
      to register its associated EID-prefixes.  In addition to the set
      of EID-prefixes to register, the message includes one or more
      RLOCs to be be used by the Map Server when forwarding Map-Requests
      (re-formatted as Encapsulated Map-Requests) received through the
      database mapping system.  An ETR may request that the Map Server
      answer Map-Requests on its behalf by setting the "proxy-map-reply"
      flag (P-bit) in the message.

   Map-Notify message:   a LISP message sent by a Map Server to an ETR
      to confirm that a Map-Register has been received and processed.
      An ETR requests that a Map-Notify be returned by setting the
      "want-map-notify" or "M" bit in the Map-Register message.  Unlike
      a Map-Reply, a Map-Notify uses UDP port 4342 for both source and

   For definitions of other terms, notably Map-Request, Map-Reply,
   Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR), please
   consult the LISP specification [LISP].

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3.  Basic Overview

   A Map Server is a device which publishes EID-prefixes in a LISP
   mapping database on behalf of a set of ETRs.  When it receives a Map
   Request (typically from an ITR) it consults the mapping database to
   find an ETR that can answer with the set of RLOCs for an EID-prefix.
   To publish its EID-prefixes, an ETR periodically sends Map-Register
   messages to the Map Server.  A Map-Register message contains a list
   of EID-prefixes plus a set of RLOCs that can be used to reach the ETR
   when a Map Server needs to forward a Map-Request to it.

   When LISP+ALT is used as the mapping database, a Map Server connects
   to ALT network and acts as a "last-hop" ALT router.  Intermediate ALT
   routers forward Map-Requests to the Map Server that advertises a
   particular EID-prefix and the Map Server forwards them to the owning
   ETR, which responds with Map-Reply messages.

   A Map Resolver receives Encapsulated Map-Requests from its client
   ITRs and uses a mapping database system to find the appropriate ETR
   to answer those requests.  On a LISP+ALT network, a Map Resolver acts
   as a "first-hop" ALT router.  It has GRE tunnels configured to other
   ALT routers and uses BGP to learn paths to ETRs for different
   prefixes in the LISP+ALT database.  The Map Resolver uses this path
   information to forward Map-Requests over the ALT to the correct ETRs.

   Note that while it is conceivable that a Map Resolver could cache
   responses to improve performance, issues surrounding cache management
   will need to be resolved for doing so to be reliable and practical.
   As initially deployed, Map Resolvers will operate only in a non-
   caching mode, de-decapsulating and forwarding Encapsulated Map
   Requests received from ITRs.  Any specification of caching
   functionality is left for future work.

   Note that a single device can implement the functions of both a Map
   Server and a Map Resolver and, in many cases, the functions will be
   co-located in that way.

   Detailed descriptions of the LISP packet types referenced by this
   document may be found in [LISP].

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4.  Interactions With Other LISP Components

4.1.  ITR EID-to-RLOC Mapping Resolution

   An ITR is configured with one or more Map Resolver addresses.  These
   addresses are "locators" (or RLOCs) and must be routeable on the
   underlying core network; they must not need to be resolved through
   LISP EID-to-RLOC mapping as that would introduce a circular
   dependency.  When using a Map Resolver, an ITR does not need to
   connect to any other database mapping system.  In particular, the ITR
   need not connect to the LISP+ALT infrastructure or implement the BGP
   and GRE protocols that it uses.

   An ITR sends an Encapsulated Map-Request to a configured Map Resolver
   when it needs an EID-to-RLOC mapping that is not found in its local
   map-cache.  Using the Map Resolver greatly reduces both the
   complexity of the ITR implementation and the costs associated with
   its operation.

   In response to an Encapsulated Map-Request, the ITR can expect one of
   the following:

   o  An immediate Negative Map-Reply (with action code of "forward-
      native", 15-minute TTL) from the Map Resolver if the Map Resolver
      can determine that the requested EID does not exist.  The ITR
      saves the EID-prefix returned in the Map-Reply in its cache,
      marking it as non-LISP-capable and knows not to attempt LISP
      encapsulation for destinations matching it.

   o  A Negative Map-Reply (with action code of "forward-native") from
      the Map Server that has an aggregate EID-covering the EID in the
      Map-Request but where the EID matches a "hole" in the aggregate.
      If the "hole" is for a LISP EID-prefix that is defined in the Map
      Server configuration but for which no ETRs are currently
      registered, a 1-minute TTL is returned.  If the "hole" is for an
      unassigned part of the aggregate, then it is not a LISP EID and a
      15-minute TTL is returned.  See Section 4.2 for discussion of
      aggregate EID-prefixes and details of Map Server EID-prefix

   o  A LISP Map-Reply from the ETR that owns the EID-to-RLOC mapping or
      possibly from a Map Server answering on behalf of the ETR.  See
      (Section 4.4) for more details on Map Resolver message processing.

   Note that an ITR may be configured to both use a Map Resolver and to
   participate in a LISP+ALT logical network.  In such a situation, the
   ITR should send Map-Requests through the ALT network for any EID-
   prefix learned via ALT BGP.  Such a configuration is expected to be

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   very rare, since there is little benefit to using a Map Resolver if
   an ITR is already using LISP+ALT.  There would be, for example, no
   need for such an ITR to send a Map-Request to a possibly non-existent
   EID (and rely on Negative Map-Replies) if it can consult the ALT
   database to verify that an EID-prefix is present before sending that

4.2.  EID Prefix Configuration and ETR Registration

   An ETR publishes its EID-prefixes on a Map Server by sending LISP
   Map-Register messages.  A Map-Register message includes
   authentication data, so prior to sending a Map-Register message, the
   ETR and Map Server must be configured with a shared secret or other
   relevant authentication information.  A Map Server's configuration
   must also include a list of the EID-prefixes for which each ETR is
   authoritative.  Upon receipt of a Map-Register from an ETR, a Map
   Server accepts only EID-prefixes that are configured for that ETR.
   Failure to implement such a check would leave the mapping system
   vulnerable to trivial EID-prefix hijacking attacks.  As developers
   and operators gain experience with the mapping system, additional,
   stronger security measures may be added to the registration process.

   In addition to the set of EID-prefixes defined for each ETR that may
   register, a Map Server is typically also configured with one or more
   aggregate prefixes that define the part of the EID numbering space
   assigned to it.  When LISP+ALT is the database in use, aggregate EID-
   prefixes are implemented as discard routes and advertised into ALT
   BGP.  The existance of aggregate EID-prefixes in a Map Server's
   database means that it may receive Map Requests for EID-prefixes that
   match an aggregate but do not match a registered prefix; Section 4.3
   describes how this is handled.

   Map-Register messages are sent periodically from an ETR to a Map
   Server with a suggested interval between messages of one minute.  A
   Map Server should time-out and remove an ETR's registration if it has
   not received a valid Map-Register message within the past three
   minutes.  When first contacting a Map Server after restart or changes
   to its EID-to-RLOC database mappings, an ETR may initially send Map-
   Register messages at an increased frequency, up to one every 20
   seconds.  This "quick registration" period is limited to five minutes
   in duration.

   An ETR may request that a Map Server explicitly acknowledge receipt
   and processing of a Map-Register message by setting the "want-map-
   notify" ("M" bit) flag.  A Map Server that receives a Map-Register
   with this flag set will respond with a Map-Notify message.  Typical
   use of this flag by an ETR would be to set it for Map-Register
   messages sent during the initial "quick registration" with a Map

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   Server but then set it only occasionally during steady-state
   maintenance of its association with that Map Server.  Note that the
   Map-Notify message is sent to UDP destination port 4342, not to the
   source port specified in the original Map-Register message.

   Note that a one-minute minimum registration interval during
   maintenance of an ETR-MS association places a lower-bound on how
   quickly and how frequently a mapping database entry can be updated.
   This may have implications for what sorts of mobility can be
   supported directly by the mapping system; shorter registration
   intervals or other mechanisms might be needed to suopport faster
   mobility in some cases.  For a discussion on one way that faster
   mobility may be implemented for individual devices, please see

   An ETR may also request, by setting the "proxy-map-reply" flag
   (P-bit) in the Map-Register message, that a Map Server answer Map-
   Requests instead of forwarding them to the ETR.  See [LISP] for
   details on how the Map Server sets certain flags (such as those
   indicating whether the message is authoritative and how returned
   locators should be treated) when sending a Map-Reply on behalf of an
   ETR.  When an ETR requests proxy reply service, it should include all
   RLOCs for all ETRs for the EID-prefix being registered, along with
   the routable flag ("R-bit") setting for each RLOC.  The Map Server
   includes all of this information in Map Reply messages that it sends
   on behalf of the ETR.  This differs from a non-proxy registration
   since the latter need only provide one or more RLOCs for a Map Server
   to use for forwarding Map-Requests; the registration information is
   not used in Map-Replies so it being incomplete is not incorrect.

   An ETR which uses a Map Server to publish its EID-to-RLOC mappings
   does not need to participate further in the mapping database
   protocol(s).  When using a LISP+ALT mapping database, for example,
   this means that the ETR does not need to implement GRE or BGP, which
   greatly simplifies its configuration and reduces its cost of

   Note that use of a Map Server does not preclude an ETR from also
   connecting to the mapping database (i.e. it could also connect to the
   LISP+ALT network) but doing so doesn't seem particularly useful as
   the whole purpose of using a Map Server is to avoid the complexity of
   the mapping database protocols.

4.3.  Map Server Processing

   Once a Map Server has EID-prefixes registered by its client ETRs, it
   can accept and process Map-Requests for them.

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   In response to a Map-Request (received over the ALT if LISP+ALT is in
   use), the Map Server first checks to see if the destination EID
   matches a configured EID-prefix.  If there is no match, the Map
   Server returns a negative Map-Reply with action code "forward-native"
   and a 15-minute TTL.  This may occur if a Map Request is received for
   a configured aggreate EID-prefix for which no more-specific EID-
   prefix exists; it indicates the presence of a non-LISP "hole" in the
   agregate EID-prefix.

   Next, the Map Server checks to see if any ETRs have registered the
   matching EID-prefix.  If none are found, then the Map Server returns
   a negative Map-Reply with action code "forward-native" and a 1-minute

   If any of the registered ETRs for the EID-prefix have requested proxy
   reply service, then the Map Server answers the request instead of
   forwarding it.  It returns a Map-Reply with the EID-prefix, RLOCs,
   and other information learned through the registration process.

   If none of the ETRs have requested proxy reply service, then the Map
   Server re-encapsulates and forwards the resulting Encapsulated Map-
   Request to one of the registered ETRs.  It does not otherwise alter
   the Map-Request so any Map-Reply sent by the ETR is returned to the
   RLOC in the Map-Request, not to the Map Server.  Unless also acting
   as a Map Resolver, a Map Server should never receive Map-Replies; any
   such messages should be discarded without response, perhaps
   accompanied by logging of a diagnostic message if the rate of Map-
   Replies is suggestive of malicious traffic.

4.4.  Map Resolver Processing

   Upon receipt of an Encapsulated Map-Request, a Map Resolver de-
   capsulates the enclosed message then searches for the requested EID
   in its local database of mapping entries (statically configured or
   learned from associated ETRs if the Map Resolver is also a Map Server
   offering proxy reply service).  If it finds a matching entry, it
   returns a LISP Map-Reply with the known mapping.

   If the Map Resolver does not have the mapping entry and if it can
   determine that the EID is not in the mapping database (for example,
   if LISP+ALT is used, the Map Resolver will have an ALT forwarding
   table that covers the full EID space) it immediately returns a
   negative LISP Map-Reply, with action code "forward-native" and a 15-
   minute TTL.  To minimize the number of negative cache entries needed
   by an ITR, the Map Resolver should return the least-specific prefix
   which both matches the original query and does not match any EID-
   prefix known to exist in the LISP-capable infrastructure.

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   If the Map Resolver does not have sufficient information to know
   whether the EID exists, it needs to forward the Map-Request to
   another device which has more information about the EID being
   requested.  To do this, it forwards the unencapsulated Map-Request,
   with the original ITR RLOC as the source, to the mapping database
   system.  Using LISP+ALT, the Map Resolver is connected to the ALT
   network and sends the Map-Request to the next ALT hop learned from
   its ALT BGP neighbors.  The Map Resolver does not send any response
   to the ITR; since the source RLOC is that of the ITR, the ETR or Map
   Server which receives the Map-Request over the ALT and responds will
   do so directly to the ITR.

4.4.1.  Anycast Map Resolver Operation

   A Map Resolver can be set up to use "anycast", where the same address
   is assigned to multiple Map Resolvers and is propagated through IGP
   routing, to facilitate the use of a topologically-close Map Resolver
   each ITR.

   Note that Map Server associations with ETRs should not use anycast
   addresses as registrations need to be established between an ETR and
   a specific set of Map Servers, each identified by a specific
   registation association.

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5.  Open Issues and Considerations

   There are a number of issues with the Map Server and Map Resolver
   design that are not yet completely understood.  Among these are:

   o  Constants, such as those used for Map-Register frequency,
      retransmission timeouts, retransmission limits, negative Map-Reply
      TTLs, et al are subject to further refinement as more experience
      with prototype deployment is gained.

   o  Convergence time when an EID-to-RLOC mapping changes and
      mechanisms for detecting and refreshing or removing stale, cached

   o  Deployability and complexity trade-offs of implementing stronger
      security measures in both EID-prefix registration and Map-Request/
      Map-Reply processing

   o  Requirements for additional state in the registration process
      between Map Servers and ETRs

   The authors expect that experimentation on the LISP pilot network
   will help answer open questions surrounding these and other issues.

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6.  IANA Considerations

   This document makes no request of the IANA.

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7.  Security Considerations

   The 2-way LISP header nonce exchange documented in [LISP] can be used
   to avoid ITR spoofing attacks.

   To publish an authoritative EID-to-RLOC mapping with a Map Server, an
   ETR includes authentication data that is a hash of the message using
   pair-wise shared key.  An implementation must support use of HMAC-
   SHA-1-96 [RFC2104] and should support use of HMAC-SHA-256-128
   [RFC6234] (SHA-256 truncated to 128 bits).

   During experimental and prototype deployment, all authentication key
   configuration will be manual.  Should LISP and its components be
   considered for IETF standardization, further work will be required to
   follow the BCP 107 [RFC4107] recommendations on automated key

   As noted in Section 4.2, a Map Server should verify that all EID-
   prefixes registered by an ETR match configuration stored on the Map

   The currently-defined authentication mechanism for Map-Register
   messages does not provide protection against "replay" attacks by a
   "man-in-the-middle".  Additional work is needed in this area.

   [LISP-SEC] defines a proposed mechanism for providing origin
   authentication, integrity, anti-replay protection, and prevention of
   man-in-the-middle and "overclaiming" attacks on the Map-Request/
   Map-Reply exchange.  Work is ongoing on this and other proposals for
   resolving these open security issues

   While beyond the scope of securing an individual Map Server or Map
   Resolver, it should be noted that a BGP-based LISP+ALT network (if
   ALT is used as the mapping database infrastructure) can take
   advantage standards work on adding security to BGP.

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8.  References

8.1.  Normative References

   [ALT]      Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP-ALT)",
              draft-ietf-lisp-alt-10.txt (work in progress),
              October 2011.

   [LISP]     Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-20.txt (work in progress), January 2012.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

8.2.  Informative References

   [CONS]     Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
              Content distribution Overlay Network Service for LISP",
              draft-meyer-lisp-cons-04.txt (work in progress),
              April 2008.

   [LISP-MN]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
              Mobile Node Architecture", draft-meyer-lisp-mn-05.txt
              (work in progress), May 2011.

              Maino, F., Ermagan, V., Cabellos, A., Sanchez, D., and O.
              Bonaventure, "LISP-Security", draft-ietf-lisp-sec-00.txt
              (work in progress), July 2011.

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

   [RFC4107]  Bellovin, S. and R. Housley, "Guidelines for Cryptographic
              Key Management", BCP 107, RFC 4107, June 2005.

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Appendix A.  Acknowledgments

   The authors would like to thank Greg Schudel, Darrel Lewis, John
   Zwiebel, Andrew Partan, Dave Meyer, Isidor Kouvelas, Jesper Skriver,
   Fabio Maino, and members of the mailing list for their
   feedback and helpful suggestions.

   Special thanks are due to Noel Chiappa for his extensive work on
   caching with LISP-CONS, some of which may be used by Map Resolvers.

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Authors' Addresses

   Vince Fuller
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


   Dino   Farinacci
   cisco Systems
   Tasman Drive
   San Jose, CA  95134


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