Transcript IP Over ATM: Issues

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
ATM Network
IP Host 2
ATM
NETWORK
IP Host 3
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
(Multiprotocol Encapsulation)
VC Multiplexing
(VC based Encapsulation)
(“NULL”Encapsulation)
PACKET ENCAPSULATION (RFC 1483)
Scenario:
Different Protocols
IP
Router
IPX AppleTalk
ATM Switch
Router
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
3Bytes
LLC
3Bytes
OUI
2Bytes
PID
0xAA-AA-03 0x00-00-00 0x08-00
IP Packet
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.
IPX
IP
Apple Talk
AppleTalk
IPX
IP
VCc
VCa
VCb
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 & multiprotocol 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
ATM_ARP
Server
LIS
Host
Host
Host
Host
Logical
IP
Subnet 1
LIS
LIS
Host
Logical
IP
Subnet 2
Logical
IP
Subnet 3
Host
ATM_ARP
Server
ATM_ARP
IP Router
Server
IP Router
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 Host 1
LIS 1
(ATM Network)
IP Host 2
IP Router
ATM ARP Server
LIS 2
IP Host 3
ATM Network
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
IP address=176.13.11.1
ATM address=AAA
ATM
Switch
IP Client# 2
IP address=176.13.11.2
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
ATM address=ZZZ
IP Client #1
IP address=176.13.11.1
ATM address=AAA
ATM
Switch
Setup VC
InATMARP_Req (IP addr of client #1???)
InATMARP_Reply (176.13.11.1)
ATMARP
Server
IP Client #2
IPaddress=176.13.11.2
ATM address=BBB
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.
IP Client# 1
IP address=176.13.11.1
ATM address=AAA
ATMARP server
IP address=176.13.11.99
ATM address=ZZZ
ATM
Switch
ATMARP_Req (IP addr of Client #2, ATM addr ???)
ATMARP_Reply (ATM addr = BBB)
Setup VC and Send Data
IP Client# 2
IP address=176.13.11.2
ATM address=BBB
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 ATMARP 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
Switch
Registration
Host 1
ATM_ARP
Server
Destination
Switch
Host 2
Set Up
Set Up
Connect
Connect
Connection Established
InARP request
Connection
Establishment
Address
Resolution
InARP RP
ARP Request
ARP Response
Set Up
Set Up
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 Host 1
LIS 1
(ATM Network)
IP Host 2
IP Router
ATM ARP Server
LIS 2
IP Host 3
ATM Network
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
LIS
A.1
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 multicastcapable 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.2
A.1
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-tomultipoint 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
t
Hos
t
LIS
(ATM
Network)
LIS
(ATM
Network)
Go through a router that is aRouter
member of multiple logical IP
subnets. This router may become a bottleneck.
Solution
NHRP
Router
Router
ATM
Switch
ATM
Switch
ATM
Switch
ATM
Switch
ATM
Switch
Subnet X
ATM
Switch
ATM
Switch
ATM
Switch
ATM
Switch
Subnet Y
VC
Data
ATM
Switch
ATM
Switch
ATM
Switch
Subnet Z
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
Switch
ATM
Switch
Subnet ATM
Switch
X
ATM
Switch
X.1
ATM
Switch
ATM
Switch
Subnet ATM
Switch
Y
ATM
Switch
ATM
Switch
ATM
Switch
Subnet ATM
Switch
Z
ATM
Switch
Z.3
NHRP Registration Request
NHRP Registration Request
NHRP Registration Reply
NHRP Registration Reply
NHRP ADDRESS RESOLUTION
NHS X
NHS Z
ATM
Switch
Subnet X
ATM
Switch
ATM
Switch
X.1
ATM
Switch
ATM
Switch
ATM
Switch
ATM
Switch
Subnet Y
ATM
Switch
ATM
Switch
NHRP Resolution Request
NHRP Resolution Reply
Subnet Z
First Packet
ATM
Switch
ATM
Switch
Z.3
IP address = Z.3
ATM address = BBB
IP address = X.1
ATM address = AAA
First Packet
ATM
Switch
First Packet
NHRP Resolution Request
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 nonauthoritative 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
IP over ATM
MAC Layer Address Mapping
ATM Address Mapping
ATM_ARP Server only
IP Address
ATM Address
Mapping of Integrated Services
Internet into ATM
Application
Integrated
Service
Internet
RSVP
PIM
Flow
Specs
Flow
IDs
Packet
Scheduling
ATM
ATM
Signaling
VC
Routing
Traffic
Contract
VPI/VCI
Traffic
Management