IP Over ATM Issues

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					             8. IP Over ATM

• Set of IP hosts within a same IP domain
  (subnet) communicate with each other
  directly over ATM network.
• The IP hosts outside their subnet (domain)
 communicate with other IP hosts in
 another subnet via an IP router.
CASE 1:



                            IP Host 3
  IP Host 1


              ATM Network

  IP Host 2
                            IP Host 4
                  CASE 2:


                      IP Router




IP Host 1                                   IP Host 3
            ATM Network           ATM
                                  NETWORK

IP Host 2                                   IP Host 4
                 IP Over ATM

• OVERLAY MODEL  IP over ATM

• PEER MODEL  MULTIPROTOCOL
                         LABEL SWITCHING
                         (MPLS)
 Integrated ATM switching and IP Routing Function.
 No Address Resolution Protocol.
 FRAMEWORK for IP over ATM
1. Packet Encapsulation

2. Address Resolution

3. Multicasting

4. Large Network (Scalability)
         DETAILED FRAMEWORK
1. How many VC’s do we need for n protocols?
  i.e., Define a method to transport multiple types of network
  or link layer packets across an ATM connection and also for
  MUXing multiple packet types on the same connection.
 Encapsulating IP packets in ATM AAL5 cells?
   Packet Encapsulation [RFC 1483]

2. How to find ATM addresses from IP
  addresses?
Address Resolution [RFC 1577]
    DETAILED FRAMEWORK

3. How to handle multicast?
    MARS [RFC 2022]

4. How do we go through n subnets
   on a large ATM network?
    NHRP
  PACKET ENCAPSULATION (RFC 1483)
A node that receives a network layer packet across an ATM connection to know what kind of
packet has been received, and to what application or higher level entity to pass the packet to;
hence the packet must be prefixed with a MUX field.



• Goal: Encapsulating IP packets in
    ATM AAL5 cells



LLC/SNAP Encapsulation                                          VC Multiplexing
(Multiprotocol Encapsulation)                            (VC based Encapsulation)
                                                     (“NULL”Encapsulation)
 PACKET ENCAPSULATION (RFC 1483)
Scenario:
                 Different Protocols
            IP   IPX AppleTalk

       Router                                  Router
                                  ATM Switch


Given an ATM link between two routers with 3
different protocols. How many VC’s shall we set up?
 ANSWER 1: LLC/SNAP ENCAPSULATION
        Share a VC using LOGICAL LINK CONTROL (LLC)
  Subnetwork Access Protocol (SNAP).




  IP      IPX      Apple Talk                IP      IPX      Apple Talk




                      VC

Several protocols are carried over the same VC. The protocol is identified
by prefixing the IP packet with an IEEE 802.2 LLC header followed by
an IEEE 802.1a Subnet Attachment Point (SNAP) header. Encapsulations
Terminate at the LLC layer within the end system.
                LLC/SNAP ENCAPSULATION
                                                    IP Packet
           3Bytes       3Bytes      2Bytes
           LLC          OUI          PID
       0xAA-AA-03 0x00-00-00 0x08-00                IP Packet
                     8Byte header

                              AAL5 Frame

An LLC (3 bytes) /SNAP header (5 bytes) is prepended to each packet to identify
which protocol is contained in the payload. PID distinguishes one protocol from
another.
0x0800 specifies IP; 0x0806 is ARP; 0x809B is AppleTalk; 0x8137 is IPX; ..
OUI  Organizationally Unique Identifier administers the
meaning of the following 2 Octet Protocol Identifier (PID),
e.g., OUI value 0x000000  the PID as an Ethernet type.
Max Transfer Unit (MTU) size is standardized at 9180 Bytes, excluding
8 Byte header. However, the size can be negotiated up to 64K Bytes.
ANSWER 2:            VC MULTIPLEXING (“NULL” ENCAPSULATION)

Each protocol is carried over a separate VC with the protocol
type specified at connection set-up.


  IP         IPX       Apple Talk                 AppleTalk        IPX          IP


                               VCc
               VCb
       VCa



VC is terminated directly at a layer 3 endpoint. In other words, the AAL endpoints
of a VC multiplexed connection would be the layer 3 protocol entities. This means
that a VC will carry one protocol only. No MUXing. LANE encapsulation is a form of VC MUXing.
           Comparison of Both Schemes
• Sharing a VC limits the number of VCs required in an IP & multi-
 protocol environment
• However, it uses an additional 8 Byte per AAL frame as a header.
• Also an LLC/SNAP entity must be present at each endpoint to
 demultiplex the frames & pass them up to the higher layer protocol
• VC-based multiplexing is more efficient from a pure VC perspective.
• VC multiplexing results in minimal bandwidth and processing overhead.
• Moreover, because a single protocol is mapped to a single VC it may be
 easier to perform filtering and/or authentication.
• UNI Signaling is required to initiate an LLC/SNAP encapsulated SVC.
• LLC/SNAP supports multiple protocols over the same VC. Permits
 connection reuse & reduces connection set-up time.
• LLC/SNAP method is the default method for IP over ATM.
  ADDRESS RESOLUTION (RFC1577)

                                                    ATMARP
                                                     Server




• IP Address: 123.145.134.65
     ATM Address: 47.0000 1 614 999 2345.00.00.AA….
• Issue: IP Address  ATM Address translation (Logical IP Subnet Concept)
      Address Resolution Protocol (ARP)
      Inverse ATM ARP: (ATM_ARP Server sends messages to client).
• Solution: ATMARP servers
                  Architecture
                Host              Host
ATM_ARP
  Server

                        LIS          LIS
            LIS                                  Host
 Host                               Logical
                        Logical       IP
            Logical
                          IP       Subnet 3
              IP
                       Subnet 2
           Subnet 1                              Host
Host


                                                ATM_ARP
                                                  Server
                        ATM_ARP
              IP Router             IP Router
                          Server

                                                        15
                  Architecture (Cont.)
•   Hosts on subnet are assigned an IP address and PHY layer
    address (ATM).

•   IP nodes (end-systems and routers) in the ATM network are
    grouped into logical IP subnets (LIS) (with similar subnet
    addresses).

•   The nodes in one LIS communicate with those outside their
    LIS through IP routers.

•   When communicating with another host on the same subnet
    using ATM, it is necessary to resolve the destination IP
    address with the ATM address of the end-point.
               Architecture (Cont.)
•   When traversing subnet boundaries, it is necessary
    to first pass through a IP router which can
    continue to implement any filtering, access or
    security policies.
             Architecture (cont.)
• Within each LIS, there is an ATM Address
  Resolution Protocol Server (ATM_ARP) which
  performs directory services function for the nodes
  in the LIS.

• A single LIS can support many hosts and routers
  with the same IP network & subnet mask.

• Communication between any two members of the
  LIS takes place over ATM PVC or SVC.
            Configuration Requirements
                  (Intra-subnet)

            ATM ARP Server         IP Router            ATM ARP Server




IP Host 1                                                           IP Host 3
                         LIS 1                 LIS 2
                   (ATM Network)               ATM Network

IP Host 2                                                           IP Host 4
   Configuration Requirements (Cont.)
• All LIS members must use ATMARP and InATMARP in
 conjunction with an ATMARP server entity to resolve IP and
 ATM addresses when using SVCs.

• All LIS members must use InATMARP to resolve VCs to IP
 addresses when using PVCs. An ATMARP server entity is not
 required when using PVCs.

• All LIS members must be able to communicate with all other
 LIS members using an ATM PVC or SVC. This implies that the
 underlying ATM fabric can be fully meshed.
      Configuration Requirements (Cont.)
The following ATM parameters must be configured for each
 member of the LIS:

•    ATM Hardware Address : This is the ATM address of the
    individual IP host.

•    ATMARP Request Address : This is the ATM address of the
    ATMARP server for the LIS. If the LIS is using only PVCs,
    then this requirement may be null.
                        ATMARP SERVER
•   Primary purpose is to maintain a table or cache of IP address mappings.
•   At least one ATMARP server must be configured for each LIS, along with a
    specific IP and ATM address.
•   A single ATMARP server may service more than one LIS as long as it is IP and
    ATM addressable within each LIS.
•   An ATMARP server learns about the IP and ATM addresses of specific members
    (IP clients) of the LIS through the use of ATMARP and InATMARP messages
    exchanged between the ATMARP server and LIS members.
•   Finally, an ATMARP server can run on an IP host or router.

Figure shows an LIS with 2 IP clients and a stand-alone ATMARP server.
                              ATMARP server
                              IP address=176.13.11.99
                              ATM address=ZZZ



                 IP Client# 1                 ATM       IP Client# 2
                 IP address=176.13.11.1      Switch     IP address=176.13.11.2
                 ATM address=AAA                        ATM address=BBB
             ATMARP SERVER (Cont.)
The ATMARP protocol is composed of five unique message types.

  ATMARP Message                   Description

  ATMARP request     Sent from IP client to server to obtain destination ATM address, contains the
                     client’s IP address, ATM address, and the destination’s IP address

  ATMARP reply       Response from server to IP client with destination ATM address, contains the
                     client’s and destination’s IP and ATM addresses
  InATMARP request   Sent from server to IP client over VC to obtain IP address, contains the client’s
                     ATM address and the ATMARP server’s IP and ATM addresses
  InATMARP reply     Response from IP client over VC with IP address, contains the client’s and
                     Server’s IP and ATM addresses

  ATMARP NAK         Negative response to ATMARP request sent from server to IP client
                           Registration
• IP clients must first register their IP and ATM addresses with the
ATMARP server.
• This is performed by the IP client who initially establishes an SVC with
the ATMARP server.
• The IP client is able to do this because it is configured with the ATM
address of the ATMARP server.
• Next the ATMARP server sends out an InATMARP request.
• The purpose of this message is to obtain the IP address of the client.
• The client returns an InATMARP reply which will contain both the IP
and ATM addresses of the client.
• The ATMARP server checks its existing table and if there are no
duplicates, time-stamps the entry and adds it to the table.
• This entry is valid for a minimum of 20 minutes.
•
                                     Registration
• The registration process flow for IP Client #1 is shown in
Figure.
• Of course, IP Client #2 will register its own address with the
ATMARP server once it is initialized.



                         IP address=176.13.11.99        ATMARP
                         ATM address=ZZZ                 Server


IP Client #1                                                      IP Client #2
                                                ATM
IP address=176.13.11.1                                            IPaddress=176.13.11.2
                                               Switch
ATM address=AAA                                                   ATM address=BBB
                         Setup VC
          InATMARP_Req (IP addr of client #1???)
            InATMARP_Reply (176.13.11.1)
              A new client wants to join
Client Comes Up (Registers)  To establish a connection to
the ATMARP Server of its own LIS.


     Client                 ATM_ARP Server
              Inverse ARP

ATMARP Server detects the connection from the new client,
sends an inverse ARP request using the clients ATM address to
request clients’ IP address since it knows clients ATM address
through VC connection.
                ADDRESS RESOLUTION
• If IP Client #1 wishes to communicate with IP Client #2 and a
connection already exists, then the packets will immediately flow
over that connection.

• IP Client #1 may contain the ATM address of IP Client #2 in its
own ARP cache and if so, then it can immediately set up an SVC
to IP Client #2.

• However, if a connection does not already exist and IP Client #1
does not know the ATM address of IP Client #2, then the ATMARP
process is invoked.

• IP Client #1 sends an ATMARP request to the ATMARP server
that contains the source IP address, destination IP address, and
source ATM address.
                       ADDRESS RESOLUTION
• If the ATMARP server contains an IP/ATM address entry for IP Client #2,
it will return that information in an ATMARP reply message.

• IP Client #1 then knows the ATM address of IP Client #2 and can set up
an SVC.

• If not, then the ATMARP server will return an ARP NAK message.


                                  ATMARP server
                                                              IP Client# 2
         IP Client# 1             IP address=176.13.11.99     IP address=176.13.11.2
         IP address=176.13.11.1   ATM address=ZZZ             ATM address=BBB
         ATM address=AAA

                                                      ATM
                                                     Switch
       ATMARP_Req (IP addr of Client #2, ATM addr ???)
              ATMARP_Reply (ATM addr = BBB)
                Setup VC and Send Data
                        Example:
• Client in LIS 1 wants to communicate with a client in LIS 2
  must go through ROUTER 1 even though a direct VC can
  be established between two clients over the ATM network.
• Two clients are attached to two different ATM switches.
• Within this LIS  Host 2 had registered earlier with ATM-
  ARP server.
• Each node is configured with the ATM address of its
  ATM_ARP server.

• Host 1 establishes a connection to its LIS ATM_ARP Server
 and then resolves an address for Host 2 in the same LIS.


                                                            29
                      Operation of Classical IP over ATM
                                   Source                 ATM_ARP             Destination
           Host 1                                                                                     Host 2
                                   Switch                   Server              Switch
                      Set Up
       Registration




                                                Set Up
                                                Connect
                      Connect
                           Connection Established
                               InARP request
                                   InARP RP
Resolution




                                 ARP Request
 Address




                                 ARP Response

                       Set Up
 Establishment




                                                            Set Up
  Connection




                                                                                            Set Up
                                                                                            Connect
                                                            Connect

                       Connect
                                                     Connection Established
                                REVIEW:
  Suppose: A host S wants to use CLIP (Classical IP over ATM) to send packets
to another host D wthin the same LIS. S knows only the IP address of D. To set up
          a VCC through ATM. How does S resolve ATM address of D?


               ATM ARP Server         IP Router            ATM ARP Server




   IP Host 1                                                           IP Host 3
                            LIS 1                 LIS 2
                      (ATM Network)               ATM Network

   IP Host 2                                                           IP Host 4
           IP Multicasting over ATM
Reminder (Pure IP Case):
•   IP uses the CLASS D address space to send packets to
    the members of a multicast group.

•   Host and routers exchange messages using a group
    membership protocol called the Internet Group
    Management Protocol (IGMP).

•   The routers use the results of this message exchange
    along with a multicast routing protocol such as MOSPF
    to build a delivery tree from the source subnetwork to
    all other subnetworks that have members in the
    multicast group.
            IP Multicasting over ATM
 • Multicast Address Resolution Server (MARS)
 (Analog to the ATMARP Server that supports
   multicast address resolution)
• IP hosts attached to an ATM network utilize the MARS
  to track and disseminate information about multicast
  group membership.

• IP multicast senders may query the MARS when
  multicast address needs to be resolved with the ATM
  address(es) of the IP hosts participating in the group.
         IP Multicasting over ATM (Ctd)
The following should also be noted about the MARS:
•   The concept of a CLUSTER is used to define ATM hosts (or
    routers) that are participating in an ATM level multicast and
    that share a MARS.
•    A cluster is mapped to a single LIS but it is possible to extend
    the MARS to support a single cluster over multiple LISs.


•   However, that would require support for multicast routing (e.g.,
    MOSPF, PIM) over ATM, which is an area that requires further
    study.

•   So for now consider a one-to-one relationship between LIS and
    CLUSTER.
• But instead of maintaining a table of IP to ATM
  address pairs, it holds an extended table consisting
  of IP group addresses and then the ATM addresses
  of the specific CLUSTER MEMBERS.
  This is called a HOST MAP.

• For example, an entry for members belonging
  to multicast group 232.200.200.1 might look like:
{232.200.200.1, ATM Address 1, ATM
Address 2, …, ATM Address N}
Example: A Cluster with a MARS & 3
 Cluster Members or MARS Clients
                         MARS




       A.1                           LIS       A.2



                               A.3

             Pt-Pt VC between IP client and MARS
             Pt-Mpt ClusterControlVC
• Clients who wish to participate in a multicast group
  establish a point-to-point VC with the MARS.
• Clients register with the MARS by sending a
  MARS_JOIN message containing the “all nodes” group
  address (224.0.0.1) as described in RFC 1112.
• The MARS will then add the client as a leaf on its
  ClusterControlVC.
• The ClusterControlVC is a point-to-multipoint VC that
  is established between the MARS and all multicast-
  capable cluster members (hosts or routers).
• The ClusterControlVC is used by the MARS to
  distribute group membership updates to all members of
  the cluster.
•   For example, after host A.2 registers, the MARS will send a
    MARS_JOIN message out over its ClusterControlVC to all
    members, indicating that host A.2 has registered and is
    multicast-capable.
•   Clients who wish to join or leave a specific multicast group
    will send a MARS_JOIN or MARS_LEAVE message to the
    MARS containing one or more IP group addresses.
•   Again, this information will be propagated to other cluster
    members over the ClusterControlVC so that sources (roots)
    can add to or prune their multicast trees.
•   Clients send a MARS_REQUEST to the MARS seeking
    address resolution of a specific IP group address.
•   MARS responds with a MARS_MULTI message which
    contains the HOST MAP for the IP group address.
Example  Join Address Resolution Flow
        MARS-REQUEST and MARS-MULTI Flows


                 MARS




                       LIS

  A.1                                       A.2



                        A.3
• Hosts A.2 and A.3 forward MARS_JOIN messages up to
the MARS indicating they wish to join multicast group
XYZ.
• The MARS redirects these messages out over the
ClusterControlVC.
• Host A.1 wishes to send packets to group address XYZ.
• It issues a MARS_REQUEST message to the MARS
which returns a MARS_MULTI message that contains a
HOST MAP of (XYZ,A.2,A.3).
• A.1 now has sufficient information to establish a point-to-
multipoint VC with the group members A.2 and A.3, and
will begin multicasting.
   Next Hop Resolution Protocol (for Inter-Subnets)
               (NHRP: pronounced nerp)
    Hos                                             Hos
     t                                               t



               LIS                     LIS
                (ATM                  (ATM
              Network)               Network)




                            Router
Go through a router that is a member of multiple logical IP
subnets. This router may become a bottleneck.
  Solution                       NHRP
                       Router                              Router
          ATM                             ATM                             ATM
         Switch                          Switch                          Switch
 ATM               ATM           ATM               ATM           ATM               ATM
Switch            Switch        Switch            Switch        Switch            Switch
          ATM                             ATM                             ATM
         Switch                          Switch                          Switch

    Subnet X                       Subnet Y                         Subnet Z



                                         VC
                                         Data
               NHRP (Addendum)
• Main Objective: Find the most efficient shortcut path
through ATM network so that intermediate IP routers can be
bypassed.
• Recall: Previously an IP router had to forward packets
between 2 LISs. CLIP model resolves only the ATM address
that belongs to the same LIS. CLIP model requires an IP
router to perform packet forwarding between two different
LISs.


• NHRP: provides shortcuts to traverse multiple LISs making
it more suitable for larger networks.
                           NHRP
• It is an address resolution technique for resolving IP addresses
with ATM addresses in a multiple subnet environment.
• The purpose of NHRP is to provide a host or router with the
ATM address of a destination IP address so that one or more
layer-3 hops can be bypassed by using a direct connection over
the ATM network.
• NHRP can be considered an extension to the ATMARP process
described in RFC1577.
• Whereas ATMARP is used to map IP and ATM addresses in a
single LIS, NHRP is used to map IP and ATM addresses in a
multiple LIS environment contained within a single ATM network.
                   NHRP Terminology
1.   NON-BROADCAST MULTI-ACCESS NETWORK (NBMA)
An NBMA network is defined as:
* Does not support an inherent broadcast or multicast capability.
* Enables any host (or router) attached to the NBMA network to
    communicate directly with another host on the same NBMA network.
     ATM, Frame Relay, SMDS, and X.25 are all examples of NBMA
     networks. An NBMA ATM network may contain one or more LISs.
* The NBMA is partitioned into administrative domains.
       Logical NBMA Subnets (LNS)
* Each LNS is served by an NHS (Next Hop Server)
               NHRP Terminology (Cont.)
2. NEXT HOP SERVER (NHS)
(These are responsible for answering NHRP resolution
requests by means of NHRP replies.)

• NHS serves a set of hosts (or NHRP stations) in the NBMA network and answers
NHRP resolution requests from these stations called NHC (Next Hop Clients).
• Both NHS and NHC contain a CACHE    or table of IP & ATM addresses for devices
attached to the ATM network (Address Resolution Cache).
• If the desired destination IP address is not on the ATM network, then the NHS will
provide the ATM address of the router nearest to the destination.
• The NHS should run on a router so as to facilitate forwarding of NHRP requests,
replies, and other messages over the default-routed path.
• The NHS responds to queries from NHRP clients.
• The NHS serves a specific set or domain of NHRP clients for whom it is
responsible.
             NHRP Terminology (Cont.)
3. NEXT HOP CLIENTS (NHC)
•    NHRP cloud contains entities called NHCs.
•   These are responsible for initiating NHRP resolution
     request packets.
REMARK:
• Both NHC and NHS maintain an ADDRESS RESOLUTION
    CACHE.
• An NHC in NHRP replaces an ATMARP client in CLIP
    (Classical IP over ATM Case)
• NHS replaces an ATMARP server.
               NHRP Configuration
• NHRP clients must be attached to an ATM network and
  must be configured with the ATM address of the NHS
 that is serving the client. Alternatively, it should have a
 means of locating its NHS.

• Techniques under consideration involving other server
 location requirements such as ATMARP and MARS are
 a group address and a configuration server.

• NHRP can run on an ATM-attached host or router.
 The NHS will likely be located on a station’s peer or
 default router.
         NHRP Configuration (Cont.)
• NHRP clients can be serviced by more than one NHS.
• NHRP Servers are configured with their own IP and ATM
addresses, a set of IP address prefixes that correspond to the
domain of NHRP clients it is serving, and an NBMA (ATM)
network identifier.
• If the NHRP server is located on an egress router attached
to a non-ATM network, then the NHRP server must exchange
routing information between the ATM and non-ATM
network.
            NHRP Client Registration
• NHRP clients register with their NHRP server in one of the
two ways:

1- Manual Configuration
2- NHRP Registration Packets
• The NHRP registration packet contains the following
information along with additional values:
{NHC’s ATMaddress, NHC’s IPaddress, NHS’s IPaddress}

• With this information, the NHRP server can begin to build
its table of IP and ATM addresses.
                  NHRP Client Registration
                            NHS X                            NHS Z



          ATM                                 ATM                              ATM
         Switch                              Switch                           Switch
 ATM     Subnet ATM                  ATM     Subnet ATM               ATM     Subnet ATM
Switch     X    Switch              Switch     Y    Switch           Switch     Z    Switch

          ATM                                 ATM                              ATM
         Switch                              Switch                           Switch



          X.1                                                                    Z.3


NHRP Registration Request                                            NHRP Registration Request


  NHRP Registration Reply                                              NHRP Registration Reply
                        NHRP ADDRESS RESOLUTION
                                  NHS X                                    NHS Z



                                                     ATM                                          ATM
               ATM                                                                                Switch
               Switch                                Switch


                                                                  ATM              ATM           Subnet Z   ATM
  ATM         Subnet X        ATM         ATM       Subnet Y                                                Switch
                                          Switch                  Switch           Switch
  Switch                      Switch

                                                      ATM                                          ATM
                ATM                                                                                Switch
                Switch                                Switch
                                                                                                                     Z.3
X.1
           IP address = X.1                                                         IP address = Z.3
           ATM address = AAA                                                        ATM address = BBB

               First Packet
                                                   First Packet                             First Packet
           NHRP Resolution Request
                                               NHRP Resolution Request
           NHRP Resolution Reply               NHRP Resolution Reply
                                                 Setup SVC
                                                    Data

      A single NBMA ATM network that contains 2 LISs: X and Z. Actually 3 if we
      count the LIS connecting the two routers  omitted.
                NHRP ADDRESS RESOLUTION
• The LISs are connected by two routers that serve as NHRP servers
  for subnets X and Z, respectively.
• The routers are running a normal intra-AS routing protocol, OSPF, and
  are connected by an ATM PVC so they are exchanging routing
  information.
• The station attached to subnet X with the IP address of X.1 wishes
  to communicate with station Z.3.

•   Station X.1 builds a packet and addresses it to Z.3.
•   If Z.3 ATM address known, then X.1 uses an existing VCC to send its data.
•   If not, I.e., X.1 does not know the ATM address of Z.3, then it sends NHRP.
•   This packet is forwarded over an existing ATM VC to the default router.
•   This causes X.1 to send a NHRP Next Hop Resolution Request message to NHS
    X with the following information: [AAA, X.1, Z.3].
•   Station X.1 may also opt to hold onto the packet until a NHRP reply is received
    or drop it.
•   The first option, the default, is the better choice because that allows data to
    flow over the default-routed path.
               NHRP ADDRESS RESOLUTION
•   NHS X checks to see if it serves station Z.3.
•   It also checks to see if it has an entry in its cache for Z.3.
•   SUPPOSE Neither is true so the NHRP (Next Hop Resolution
    Request) is forwarded to the adjacent NHRP server, NHS Z.
•   NHS Z receives the NHRP Next Hop Resolution Request from NHS X.
•   NHS Z determines that it serves the destination IP address contained
    in the request message.
•   An entry is contained in the cache or table of NHS Z which contains an
    IP to ATM address mapping for the destination IP address of Z.3.
•   NHS Z resolves the destination IP address, Z.3, with its matching ATM
    address, BBB.
•    It places this information in a NHRP Next Hop Resolution Reply and
    returns it to station X.1 over a default-routed path that the request
    came from.
             NHRP ADDRESS RESOLUTION
•   The NHRP Next Hop Resolution Reply could flow directly back to the
    initiator X.1 if

(1) A VC exists between station X.1 and NHS Z,
(2) An NHRP Reverse NHS record Extension is not included in the
    request message, and
(3) The authentication policy permits direct communication between the
    initiator, station X.1, NHS Z.
(4) Sending a direct response back to the NHRP initiator may save time
    but does not enable any of the intermediate NHSs to cache information
    contained in the NRP Next Hop Resolution Reply messages.

• As the NHRP Resolution Reply flows back to station X.1, NHS X may
  cache the information contained in the packet.
• This means it could add the entry of [Z.3, BBB] into its cache.
              NHRP ADDRESS RESOLUTION
• This information could be used by NHS X to provide a non-
  authoritative NHRP Next Hop Resolution Reply for another
  station on subnet X that wishes to communicate DIRECTLY
  WITH STATION Z.3.

•    An authoritative NHRP Next Hop resolution reply is the one
    that is generated by the NHS that directly serves the NHRP
    client.

•    If a NHRP client generates an authoritative resolution
    request, then only the serving NHS can respond
    authoritatively.

•     If a NHRP client generates a non-authoritative resolution
    request, then any NHS that can resolve the request can
    respond.
             NHRP ADDRESS RESOLUTION
• Nonauthoritative reply speeds up the Address Resolution
  Process.

•   However, we need to increase the CACHE SIZE requirement
    at the NHS.

•   Another disadvantage is that when IP-ATM address binding
    at the destination changes, a transit NHS will respond with a
    wrong address resolution reply.
         NHRP ADDRESS RESOLUTION

• Station X.1 will receive a NHRP Next Hop
 Resolution Reply and take two actions,

     (1) Cache the information contained in
         the reply and

     (2) Establish an ATM SVC directly to station
         Z.3 and begin data transmission.
      REINVENTING IP over ATM

• Ipsilon Networks  IP Switching
• Toshiba  Cell Switching Router
• Cisco  Tag Switching
• IBM  Aggregate Route Based IP Switching (ARIS)
• IETF  MPLS (MultiProtocol Label Switching)
    Difference of LANE and IP over ATM
•   LANE hides the layers above layer 2 from ATM fabric.
•   Consequent Applications running over a LANE network cannot take
    advantage of QoS capabilities of the ATM.

    LANE        Address Resolution Process Overhead is high.

                IP Address                 MAC Layer Address Mapping
                MAC Layer Address          ATM Address Mapping


    IP over ATM         ATM_ARP Server only

                        IP Address       ATM Address
         Mapping of Integrated Services
             Internet into ATM
                         Application


Integrated
  Service                               Flow       Flow       Packet
              RSVP         PIM          Specs               Scheduling
 Internet                                           IDs




               ATM          VC          Traffic               Traffic
  ATM
             Signaling
                                                  VPI/VCI   Management
                          Routing      Contract

				
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