Origins of MPLS. David Larrabeiti Piotr Pacyna. Dpto. de Ingeniería a Telemática Universidad Carlos III de Madrid

David

David LarrabeitiLarrabeiti Piotr

Piotr PacynaPacyna

Dpto. de Ingenier

Dpto. de Ingenieríía Telema Telemááticatica Universidad Carlos III de Madrid Universidad Carlos III de Madrid

Origins

MPLS 1

Departamento de Ingeniería Telemática

Programme authors and contributors

Lecturers (Spanish course):

‹

David Larrabeiti López

‹

José Félix Kukielka

Supporting lecturers (English course)

:

‹

Jorg Diederich

‹

Huw Oliver

Before MPLS: Integration of IP and ATM

(Server-Based)

‹ Initial solutions:

z LAN Emulation (ATM Forum, 1995, 1997) z CLIP: Classical IP over ATM (IETF, 1994)

‹ Partial Improvements:

z NHRP: Hop-by-hop address resolution for short-cut VCs (IETF, 1996) z MARS: Multicast address resolution (IETF, 1996)

‹ Integration:

z MPOA: Multiprotocol over ATM (ATM Forum, 1997, 1999)

‹ Server-based schemes:

z Need new protocols

z Server: Potential single points of failure

ƒ Need redundant servers

ƒ Protocols to ensure consistency among servers

MPLS 3

Departamento de Ingeniería Telemática

Before MPLS: Integration of IP and ATM

(Overlay Approach)

‹

Overlay approach:

z Two independent schemes (one ATM and one IP) ƒ For addressing, routing, resource reservation,… z ATM network transparent to IP routers

ƒ Need to interconnect all routers directly using VCs

¾Else: Need another router in the network Æ potential bottleneck

ƒ Full mesh structure in the ATM network:

¾O(N2_{) SVCs}

¾ Insufficient scalability

¾

Label Switching: Combine

z Functionality of a router (IP) z Advantages of a switch (ATM)

Overlay Network: Scalability Problem

‹ Number of SVCs between routers growing faster than number of routers

‹ Signaling eventually becomes bottleneck

Router Router Router _Router Router Router Router Switch Switch Switch Switch VC VC V C VC VC VC VC VC V C VC VC VC

MPLS 5

Departamento de Ingeniería Telemática

Disadvantages of the IP/ATM integration

approach

‹

Based on servers

z => protocols

z => single points of failure => redundancy, synchronisation

‹

Complexity

‹

OVERLAY Approach

z 2 independent schemes for

ƒ Addresses, routing, reservations, logical IP topology/physical

ATM

z Lack of scalability

ƒ FULL MESH

¾O(N2_{) SVCs; O(N}3_{) messages after link failure}

¾Signalling is a bottleneck

¿is it possible to combine the advantages of IP and ATM?

¿is it possible to have devices with the functionality of a

Label Switching: Objectives

‹ Higher performance and scalability

z Exponential growth of the Internet (traffic + number of nodes)

‹ Lower complexity and higher robustness

z E.g. in the overlay model: two control planes

ƒ ATM: PNNI, UNI, ... ƒ IP: OSPF, BGP,...

¾ Complex mapping necessary Î better avoid this

z Achieve lower costs per router / switch + higher robustness

‹ Enable evolution of control mechanisms:

z Fixed forwarding scheme (e.g. in hardware)

z Exchangeable control scheme (e.g. routing protocol) ¾ Very important objective (but not so well-known)

¾ Integrate IP routers and switches (mainly ATM)

¾ Use ATM switching technology (others possible)

History

Initial Vendor Proposals

‹ Cell Switch Router, Toshiba (1994)

z First scheme to control ATM switches by IP protocols

z Avoid using ATM signaling and mapping functions to reduce complexity

‹ IP Switching, Ipsilon (1996) ‹ Tag Switching, Cisco

z Different from IP Switching and cell switch routers z Basically the basis for MPLS

‹ Aggregate Router-Based IP Switching (ARIS), IBM

z Similar to Tag Switching

¾ Differences in the way to assign and maintain labels ‹ Standardization in the IETF:

z MPLS: MultiProtocol Label Switching

MPLS 9

Departamento de Ingeniería Telemática

IP switching

‹

Ipsilon, 1995 RFC1953, 1954, 1987

‹

IP switch: ATM switch without ATM routing

protocol, without signalling and with IP routing

control

GSMP: General Switch Management Protocol

IFMP: Ipsilon Flow Management Protocol ATM Switch PC with Router-Based Software IP ATM IFMP GSMP LLC/SNAP+AAL5

Control Plane in Nodes

MPLS 11

Departamento de Ingeniería Telemática

IP Switching: Basic Function

‹

Initially:

z All traffic between IP switches sent over a default VC z Routing controlled by the switch controller

‹

Each controller:

z Detects “sustained” flows locally

z Assigns a VPI/VCI to the flow (the label) z Tells the neighbor about the label

ƒ IFMP: Ipsilon Flow Management Protocol

‹

Move from IP-based forwarding to switched forwarding

IP Switching: Normal Forwarding

Default

VPI/VCI

Flow selection

Send certain packets

with new VPI/VCI

MPLS 13

Departamento de Ingeniería Telemática

IP Switching: Direct Forwarding

Controller ATM Previous node Next node

Default

VPI/VCI

Selection of

the same flow

Send these packets

with new VPI/VCI

IP Switching: Flow Detection

‹

Discussion:

z IP Switching is a simple solution

‹

Problem:

z Which flows shall be switched?

‹

Solution: Data-driven

z Look at the application layer protocol

ƒ Candidates: FTP, telnet, HTTP, audio and video ƒ Cross-layer interaction to improve performance

‹

Is that efficient?

z According to Ipsilon: Yes

MPLS 15

Departamento de Ingeniería Telemática

Toshiba CSR RFC2098, 2129

‹

Cell Switch Router, Toshiba (1994)

z

Detection of sustained flows + Label assignment

(FANP)

z

Preconfigured short cuts

z

Objective:LIS-LIS communications

z

Works over conventional ATM network (only)

Implements PNNI, ATM signaling

Aggregate Route-Based IP Switching

(ARIS)

‹

Concept of aggregations

z Aggregate routes on their way to the destination

z ATM: VC-merging

‹

Concept of ordered

control

z Assign labels in a coordinated way

‹

More details to follow...

MPLS 17

Departamento de Ingeniería Telemática

MPLS

‹

Standardization in the IETF

z BOF session December 1996 initiated WG

ƒ Main problem: Different label switching approaches not

interoperable without standardization ¾Industry initiative

‹

Integrate the existing proposals

z Basically Tag Switching from Cisco and ARIS from IBM

‹

Multiprotocol

z Independent of layers below label switching ƒ Ethernet, ATM, FDDI, FR, PPP, …

ƒ SDH, optical switching...

z MPLS forwarding independent from layers above ƒ IPv4, IPv6, IPX, AppleTalk, …

References

‹ [1] MPLS Technology and Applications. Bruce Davie, Yakov Rekhter. Morgan Kaufmann. 2000.

‹ [2] Transparencias del tutorial de MPLS de Nortel Networks impartido por Ricardo Borrajo (profesor asociado) en la Universidad Carlos III de Madrid.

‹ [3] Eric Osborne, Ajay Simha. Traffic engineering with MPLS. 1ª Edición. Cisco Press , 2002.

‹ [4] MPLS-based VPNs. Tomsu, Wieser. 2002.