ip atm 0203 - university of...

© Dr. Z. Sun

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IP and ATM Internetworking (CIPA, LANE & MPLS)

Dr. Zhili SUNUniversity of Surrey

GuildfordSurrey

GU2 5XHTel: 01483 68 9493Fax: 01483 68 6011

Email: [email protected]

Components of DATA and INTERNET NETWORKING MSc MODULE

(EEM.din, Linked UG EE4.din)

IP and ATM Internetworking(CIPA, LANE & MPLS)

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Table of Contents

1. Classical IP over ATM (CIPA)2. LAN Emulation (LANE)3. Multi-Protocol Label Switch (MPLS)4. Summary

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1. Classical IP Over ATM (CIPA)

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Why IP over ATM?

■ The motivation of “IP over ATM” is to support TCP/IP and applications based on TCP/IP which are widely used long before ATM is developed and to allow interoperability between ATM networks and existing networks

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IP Over ATM – Protocol Stack

Application

TCP/UDP Layer

IP Layer

AAL 5

ATM Layer

Physical Layer

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Classical IP Over ATM

■ The “Classical IP Over ATM” provides mechanisms for encapsulation and transmission of IP network layer packets across an ATM Adaptive Layer (AAL) 5 connection

■ It provides a mechanism for the resolution of IP addresses to their corresponding ATM addresses (this is part of the "classical IP over ATM" protocol)

■ It includes the emerging “Next Hop Resolution Protocol (NHRP)“, and

■ IP multicast over ATM via a combination of multicast servers and overlaid point to multi-point connections

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IP over ATM Encapsulation

■ Encapsulation allows for the multiplexing of multiple packet types (at the network layer) on the same connection:• Conserves connection resources• Saves on connection setup time

■ Multiplex only with UBR, ABR - VBR may require distinct flows

■ Packet must be prefixed with multiplexing field to allow node that receives a network layer packet across an ATM connection:• To know what type of packet has been received• To know what application to pass the packet to

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IP over ATM Encapsulation (cont.) - RFC 1483

■ Methods for identifying this type of information are:• Subnet Access Protocol / Logical Link Control

(LLC/SNAP) Encapsulation - type of packet identified by header (default encapsulation for IP over ATM)

• VC multiplexing - only single protocol carried across ATM connection with type of protocol identified at connectionsetup (used by LANE); used for direct connectivity between ATM connections

■ Default MTU size is 9180 bytes (+ 8 byte LLC/SNAP header = 9188 bytes) - MTU size can be negotiated up to maximum for AAL 5 (64 Kbytes)

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IP over ATM Address Resolution - RFC 1577

■ The "classical" view of IP is one in which clusters of IP nodes (hosts and routers) with similar subnet addresses are connected to nodes outside their cluster by IP routers

■ The IETF adhered to this "classical" view by grouping IP nodes into logical IP subnets (LIS) - nodes share the same IP subnet, communicate with the outside through an IP router

■ When node first "comes up" in LIS it establishes a connection with ATMARP server - the node is configured to know the ATM address of the server for address resolution

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IP over ATM Address Resolution (cont.)

■ ATMARP server (can be part of router - but 1577 recommends that it be another IP station) detects a new LIS client:• Sends Inverse ARP (have ATM address, want IP

address) request to the attaching client• Requests node’s IP and ATM addresses - stores them

in its ATMARP table• Server learn this information by observing client

messages

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■ To resolve destination IP address:• client sends ATMARP (have IP address, want ATM address)

request to server• server responds with ATMARP reply if address mapping is found• if not returns ATM_NAK

■ ATMARP server sends out periodic Inverse ARP requests to update its addresses - if no response - address eliminated

■ Once client obtains ATM address corresponding to an IP destination - set up connection to that address (ATMARP servers also keeps track of VC’s)

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Routing across ATM with the Classical mode

■ 1. Routing table maps final destination to next hop■ 2. address resolution table or server maps the next hop IP address to ATM address■ 3. Signalling creates ATM virtual connection between routers■ 4. forward packet over ATM virtual connection

131.227.10.X -> direct 131.227.23.X -> via 131.227.10.2 131.227.45.X -> via 131.227.10.3 131.227.67.X -> via 131.227.10.3

Routing 1

ATM Network

3

131.227.10.1ATM

Switch

131.227.10.2ATM

Switch

131.227.45.94

131.227.23.X

ARP Server

131.227.10.2 -> B 131.227.10.3 -> C

Address Resolution 2

A

B

131.227.10.3ATM

Switch131.227.45.X

C

131.227.67.X

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■ Disadvantages:• Communicate to host outside of LIS - go through

router even though might be able to connect directly to destination

• Routers become bottlenecks• Can’t establish connection with QoS between the

two nodes

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Next Hop Resolution Protocol (NHRP)

■ Used instead of a LIS - Non-broadcast Multi-access (NBMA) network

■ Network technology permitting multiple devices to be attached to the same network, but does not easily permit the use of broadcast mechanisms (ATM, X.25, Frame Relay, etc)

■ Could be divided into administrative domains■ NHRP applies only within domain■ Allows access to ingress points of other domains

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NHRP server (NHS)

■ NHRP server (NHS) instead of ATMARP server■ IP to ATM mapping of nodes associated with an NHS■ IP address prefixes available through routers served

by the NHS Nodes.■ Nodes are configured with ATM address of their NHS■ Then register their ATM and IP address with NHS

using registration packets

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NHS Configurations

■ “Server" mode• each server has list of destinations served by other

NHS’s• static configuration• good for only small networks

■ “Fabric" mode• servers acquire knowledge of destinations served

by other NHS’s through intra and inter domain routing protocols

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NHRP Operations

■ Routing - client sends request (in IP packet - all NMBA messages in IP packets) to its NHS asking to resolve an ATM address• if destination served by NHS - returns mapping• if not served - forwards to another NHS - same

algorithm used there• reply sent along reverse route - all NHS’s can learn of

mapping -

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NHRP Operations (cont.)

■ Future requests - respond without forwarding request■ Direct connection established after address resolution■ Optional capabilities:

• route recording • detect loops• fallback• address aggregation - return subnet mask associated

with an address (i.e. address of firewall associated with ingress NHS of an administrative domain)

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NHRP issues

■ NHRP likely used on routers for frame relay, X.25■ Enhancements needed for widespread ATM use:

• autoconfiguration (?)• multi-casting• NHRP mechanism very IP specific - everything sent

within IP packets■ RFC1577 compliant system and NHRP may not be

interoperable• have to be connected by a router• connection of either to LANE system also requires a

router

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IP over ATM Multicasting (IPMC)

■ Multicasting is a process whereby a source host or protocol entity sends a packet to multiple destinations simultaneously using a single local transmit operation

■ The more familiar cases of Unicasting and Broadcasting may be considered as special cases of Multicasting (with the packet delivered to "one" destination or "all" destinations respectively)

■ Most network layer models assume their sources may send their packets to abstract "multicast group addresses"

■ Link layer support is assumed to exist and is provided by such technologies as Ethernet

■ ATM is being utilized as a new link layer technology to support a variety of protocols including IP

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IP over ATM Multicasting (IPMC)(cont.)

■ With RFC 1483 (2), the IETF defined a multiprotocolmechanism for encapsulating and transporting packets using AAL5 over ATM Virtual Channels (VC’s)

■ Unicast connections are supported by point to point bi-directional VC’s. Multicasting is supported by point to multipoint unidirectional VC’s

■ The key limitation is that the sender must have prior knowledge of each intended recipient and explicitly establish a VC with itself as a root node and the recipients as leaf nodes

■ The Internet Draft IPMC contains more information about IP over ATM Multicasting

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The future direction of IP over ATM

■ IPng (IPv6) over ATM (internet draft)■ Support for Multicast of IP Packets over ATM

(internet draft)■ Multiprotocol Encapsulation over AAL5 (internet draft)

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Recommended Texts

■ RFC 1483, Multiprotocol Encapsulation over ATM adaptation layer 5

■ RFC 1577, Classical IP and ARP over ATM■ RFC 1755, ATM signalling Support for IP over ATM■ RFC 2022, Multicast Address Resolution (MARS)

protocols

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2. LAN Emulation (LANE)

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Characteristics of LANs

■ Connectionless traffic■ Delivery of traffic via a shared medium

• Unicast• Broadcast• Multicast

■ MAC address independent of network topology

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OSI Reference Model

■ LAN Emulation is a Data Link Function

Presentation

Session

Transport

Network

Data Link

Physical

Application

Routing: protocol dependent

Bridging: protocol independent

Repeaters

LLC

MACLAN Emulation

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Features of LAN Emulation

■ There are currently no ATM specific protocols■ Make an ATM networks looks like a LAN■ LANE is protocol independent■ Integration of ATM and non-ATM devices without

changes to application software■ Traditional LAN services are supported■ Compliance and interoperability with others■ Support multiple emulated LANs on a single ATM

network

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ATM Forum LANE

■ Separate servers for configuration, address resolution and broadcasts/multicasts

■ ATM “cloud” treated as multiple broadcast domains Emulated LAN (ELAN)

■ Emulated Ethernet (802.3) , Token ring (802.5)

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LANE Components

■ LE Client (LEC)■ LANE Configuration Server (LECS)■ LANE Server (LES) - MAC to ATM address resolution

for unicast traffic■ Broadcast/Unknown Server (BUS) - forward

multicast, broadcast and unknown unicast packets■ LECS, LES and BUS are known as LAN Emulation

Service which may be implemented in a router, switch, or other ATM attached devices

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Communication between LECs

■ Each LEC registers MAC address with LES■ When MAC-to-ATM address resolution is required

due to a outgoing data frame:• LE_ARP request sent to LES• DATA frame sent to BUS

■ The ATM address received from the LES is used to send up ATM connection and further data exchanges

■ All broadcasts, multicasts and unknown unicastshandled by BUS

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LANE Client/Server Architecture

ATM Switch

ATM Switch

ATM Switch

ATM Switch

ATM Backbone

LECS

LES

BUS

LECATM-Attached

Servers

LEC

Edge Device

ATM-Attached Client

ATM-Attached Clients

LEC

LEC

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LANE Address resolution

ATM Switch

ATM Switch

ATM Switch

ATM Switch

ATM Backbone

LECS

LES

BUS

LEC

Bridge

Edge Device

ATM-Attached Client

ATM-Attached Clients

LEC

1. MAC frame

2. A

PR re

ques

t: M

AC ta

rget

3. A

PR re

ply:

ATM

VCI

4. set-up ATM SVC

5. MAC frame

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3. Multi-Protocol Label Switching

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What is MPLS ?

�A connection-orientated forwarding mechanism

�Hop-by-hop or source routing to establish label path

�Uses labels native to the media

�Multi-level label substitution transport

�Simple core - complexity at the edge of a domain

Multi-Protocol Label Switching developed within IETF

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MPLS Terminology

MPLS: Multi-Protocol Label SwitchingLDP: Label Distribution Protocol LSP: Label Switched PathFEC: Forwarding Equivalence ClassLSR: Label Switching RouterLER: Label Edge RouterER: Explicit RouteCR: Constraint-based RouteTE: Traffic EngineeringQoS: Quality of ServiceCoS: Class of ServiceSLA: Service Level Agreement

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123

1

2

1

23

3

Dest Out

47.1 247.2 147.3 3

Dest Out

47.1 147.2 147.3 3

IP 47.1.1.1 2

3

1

Dest Out

47.1 147.2 147.3 3

Dest Out

47.1 247.2 147.3 1

Subnet 47.2

Subnet 47.1Subnet 47.3

IP Routing

IP 47.1.1.1 IP 47.1.1.1

IP 47.1.1.1

IP 47.1.1.1

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PHY

DLink

NET

T/Port

App

Router LSR

PHY

DLink

NET

T/Port

App

IP Routing vs Fast Forwarding

PHY

DLink

PHY

DLink

NET

PHY

DLink

PHY

End System End System

RoutingTable

Longest Prefix Match

FwdingTable

Complex routing decision Simple label swapping

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Forwarding Equivalence Classes

Packets are destined for different address prefixes, but can be mapped to a common pathPackets are destined for different address prefixes, but can be mapped to a common path

LSPLSR LER

FEC = “A subset of packets that are all treated the same way by a router”

The concept of FECs provides for a great deal of flexibility and scalability

In conventional routing, a packet is assigned to a FEC at each hop(i.e. L3 look-up), in MPLS it is only done once at the network ingress

IP1#L2

IP2#L2

IP1#L1

IP2#L1

IP1#L3

IP2#L3

IP1

IP2

IP1

IP2

LSRLER

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Req 47.1Map 1:12

MPLS Label Distribution

123

1

2

23

3

2

3

1

Subnet 47.2


DestI/F In

47.13

LOutI/FOut

3:501

LInI/F In

3:503

LOutI/FOut

1:401

Req 47.1Map 3:50

Req 47.1

Map 1:40

LInI/F In

1:403

LOutI/FOut

1:122

1

LInI/F In

1:123

DestI/FOut

47.12

Push Label

Swap Label

Swap Label

Pop Label

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1

1

23

IP 47.1.1.1 2

3

1

Subnet 47.2


Data goes in at one end and comes out of the other in the same sequence

LSPs are communication “pipes”

DestI/F In

47.13

LOutI/FOut

3:501

LInI/F In

3:503

LOutI/FOut

1:401

LInI/F In

1:403

LOutI/FOut

1:122

LInI/F In

1:123

DestI/FOut

47.12

Label Switched Path (LSP)

IP 47.1.1.1

IP 47.1.1.1#3:50

IP 47.1.1.1#1:40

IP 47.1.1.1#1:12

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#612

#5

Vanilla LDP builds that tree using existing IP routing tables to route the control messages

A Vanilla LSP is actually part of a tree from every source to that destination (unidirectional)

#963

#14

#99

#311

#311

#311

#311

#14

#99

#963#462

#216

“Vanilla” Label Switched Path

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Maximize utilization of links and nodes throughout the network

Select links in order to achieve required delay, grade-of-service

Spread the network traffic across network links, minimize impact of single failure

Ensure available spare link capacity for re-routing traffic on failure

Meet policy requirements imposed by the network operator

Traffic Engineering is the process of mapping traffic demand onto network resources

Purpose of traffic engineering:

Traffic Engineering

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IP routing causes data to over-utilize best paths and under-utilize less good paths

Basic LDP is fast, simple forwarding / switching, BUT data follows same route as normal IP data path causing data to over-utilize best paths and under-utilize less good paths

We need…

Why Constraint-based Routed – LDP (CR-LDP)?

A topology database that knows about link attributes

A label distribution protocol that goes where it’s told

Constraint Based Routing provides a mechanism for selecting paths based on CHOSEN Criteria (not just a one criterion)

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CR-LDP Provides…

�Simple protocol based on LDP, output of MPLS WG

�basic hop-by-hop LDP is not needed

�Runs on TCP (like LDP) = Reliable

�Hard State (like LDP) = Scalable

�Supports Traffic Engineering with QoS Support

�Both Explicit Routes and Loose routes supported

�Demonstrated Interoperability

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IP 47.1.1.1

Subnet 47.2


Least cost congestion “hot spots” can be avoided

Using Explicit Routing any chosen path can be setup across the MPLS domain

Explicitly Routed LSP using CR-LDP

Operator has routing flexibility(policy-based, QoS-based)

Pre-computed backup paths for resiliency

IP 47.1.1.1

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Label Stacking

Label stacking – facilitates scaling and inter-operator working

Carrier MPLS Domain

LSP1 LSP1

LSP2

LSP3

LSP2

LSP3

Access ProviderMPLS Domain

Access ProviderMPLS Domain

IP-A LSP1

IP-B

IP-A

IP-BLSP2

LSP1 IP-A

IP-BLSP2

LSP3

LSP3

LSP1 IP-A

IP-BLSP2

IP-A

IP-B

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Summary (1/2)

Fast forwarding based on label swapping

Decouples routing and forwarding in IP networks and can co-exist with other protocols

Facilitates the integration of ATM and IP

Enables the use of explicit routing for traffic engineering in IP networks

Promotes the partitioning of network functionality (complexity at edge)

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Summary (2/2)

Improved routing scalability through stacking of labels

MPLS is “multiprotocol” below (link layer) as well as above (network layer), providing for consistent operations, interworking across multiple technologies

MPLS positioned as end-to-end forwarding paradigm

Flexible FEC to Label binding allows for full multi-service support

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