© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Implementation of Frame Mode MPLS Introducing MPLS Networks

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v The MPLS Conceptual Model

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v VPN Topologies

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Basic MPLS Features MPLS is a switching mechanism in which packets are forwarded based on labels. Labels usually correspond to IP destination networks (equal to traditional IP forwarding). Labels can also correspond to other parameters: –Layer 3 VPN destination –Layer 2 circuit –Outgoing interface on the egress router –QoS –Source address MPLS was designed to support forwarding of non-IP protocols as well.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Basic MPLS Concepts Example Only edge routers must perform a routing lookup. Core routers switch packets based on simple label lookups and swap labels.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Router Switching Mechanisms

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Cisco IOS Platform Switching Mechanisms The Cisco IOS platform supports three IP switching mechanisms: Routing table-driven switchingprocess switching: –Full lookup is performed at every packet Cache-driven switchingfast switching: –Most recent destinations are entered in the cache –First packet is always process-switched Topology-driven switching: –CEF (prebuilt FIB table)

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Standard IP Switching Review

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v CEF Switching Review

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Architecture

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Major Components of MPLS Architecture Control plane: –Exchanges routing information and labels –Contains complex mechanisms to exchange routing information, such as OSPF, EIGRP, IS-IS, and BGP –Exchanges labels, such as LDP, BGP, and RSVP Data plane: –Forwards packets based on labels –Has a simple forwarding engine

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Control Plane Components Example Information from control plane is sent to data plane.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Labels

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v MPLS Labels MPLS technology is intended to be used anywhere, regardless of Layer 1 media and Layer 2 protocol. MPLS uses a 32-bit label field that is inserted between Layer 2 and Layer 3 headers (frame mode MPLS). MPLS over ATM uses the ATM header as the label (cell mode MPLS).

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Format MPLS uses a 32-bit label field that contains this information: 20-bit label 3-bit experimental field 1-bit bottom-of-stack indicator 8-bit TTL field

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Stack Protocol ID (PID) in a Layer 2 header specifies that the payload starts with a label (or labels) and is followed by an IP header. Bottom-of-stack bit indicates whether the next header is another label or a Layer 3 header. Receiving router uses the top label only.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Frame Mode MPLS

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Switch Routers

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Label Switch Routers LSR primarily forwards labeled packets (swap label). Edge LSR: –Labels IP packets (impose label) and forwards them into the MPLS domain –Removes labels (pop label) and forwards IP packets out of the MPLS domain

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v LSR Component Architecture

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Functions of LSRs ComponentFunctions Control planeExchanges routing information Exchanges labels Data planeForwards packets (LSRs and edge LSRs)

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Component Architecture of LSR

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Component Architecture of Edge LSR

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Summary MPLS is a switching mechanism that uses labels to forward packets. The result of using labels is that only edge routers perform a routing lookup; all the core routers simply forward packets based on labels assigned at the edge. MPLS consists of two major components: control plane and data plane. MPLS uses a 32-bit label field that contains label, experimental field, bottom-of-stack indicator, and TTL field. LSR is a device that forwards packets primarily based on labels. Edge LSR is a device that labels packets or removes labels from packets. Exchange routing information and exchange labels are part of the control plane, while forward packets is part of the data plane.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v