IP over MPLS Overview This module focuses on the IP QoS mechanisms available in combination with Multiprotocol Label Switching (MPLS). Objectives Upon completion of this module, you will be able to perform the following tasks: n Describe and configure QoS Mechanisms in Frame-mode MPLS networks n Describe and configure QoS Mechanisms in Cell-mode MPLS networks 23-2 World Wide Training Word Templates v1 Copyright 1999, Cisco Systems, Inc. MPLS Introduction Objectives Upon completion of this lesson, you will be able to perform the following tasks: n Describe basic features of MPLS n Describe Frame-mode MPLS n Describe Cell-mode MPLS Copyright 1999, Cisco Systems, Inc. Release Date: 2/1/99 23-3 © 2001, Cisco Systems, Inc. IP QoS IP over MPLS Basic MPLS Concepts Basic MPLS Concepts • Multi-protocol Label Switching (MPLS) is a new forwarding mechanism in which packets are forwarded based on labels • Labels may correspond to IP destination networks (equal to traditional IP forwarding) • Labels can also correspond to other parameters (QoS, source address, ) • MPLS was designed to support forwarding of other protocols as well Multi-protocol Label Switching (MPLS) is a switching mechanism that uses labels (numbers) to forward packets. Labels usually correspond to layer-3 destination addresses (equal to destination- based routing). Labels can also correspond to other parameters (QoS, source address, etc.). MPLS was designed to support other protocols as well. Label switching is performed regardless of the layer-3 protocol. 23-4 World Wide Training Word Templates v1 Copyright 1999, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS Example MPLS Example • Only edge routers must perform a routing lookup. • Core routers switch packets based on simple label lookups and swap labels. L=5 L=3 10.1.1.1 10.1.1.1 Routing lookup and label assignment 10.0.0.0/8 à L=5 Label swapping L=5 à L=3 Label removal and routing lookup L=3 The example in the figure illustrates a situation where the intermediary router does not have to perform a time-consuming routing lookup. Instead this router simply swaps a label with another label (5 is replaced by 3) and forwards the packet based on the received label (5). In larger networks, the result of MPLS labeling is that only the edge routers perform a routing lookup. All the core routers forward packets based on the labels. Copyright 1999, Cisco Systems, Inc. Release Date: 2/1/99 23-5 © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS vs. IP-over-ATM MPLS vs. IP-over-ATM • Layer-2 devices are IP-aware and run a routing protocol • There is no need to manually establish virtual circuits • MPLS provides a virtual full-mesh topology 10.1.1.1L=5 L=3 L=1710.1.1.1 Layer-2 devices run a layer-3 routing protocol and establish virtual circuits dynamically based on layer-3 information The example in the figure shows how MPLS is used in ATM networks to provide optimal routing across layer-2 ATM switches. In order for MPLS to work with ATM switches, the switches must be layer-3 aware (ATM switches must run a layer-3 routing protocol). Another benefit of this setup is that there is no longer a need to manually establish virtual circuits. ATM switches automatically create a full mesh of virtual circuits based on layer-3 routing information. 23-6 World Wide Training Word Templates v1 Copyright 1999, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over MPLS Traffic Engineering with MPLS Traffic Engineering with MPLS • Traffic can be forwarded based on other parameters (QoS, source, ) • Load sharing across unequal paths can be achieved Secondary OC-48 link Large site A Large site B Small site C Primary OC-192 link MPLS also supports traffic engineering. Traffic engineered tunnels can be created based on a traffic analysis to provide load balancing across unequal paths. Multiple traffic engineering tunnels can lead to the same destination but can use different paths. Traditional IP forwarding would force all traffic to use the same path based on the destination-based forwarding decision. Traffic engineering determines the path at the source based on additional parameters (available resources and constraints in the network). Copyright 1999, Cisco Systems, Inc. Release Date: 2/1/99 23-7 © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS Architecture MPLS Architecture • MPLS has two major components: • Control plane – exchanges layer-3 routing information and labels • Data plane – forwards packets based on labels • Control plane contains complex mechanisms to exchange routing information (OSPF, EIGRP, IS-IS, BGP, ) and labels (TDP, LDP, BGP, RSVP, ) • Control plane maintains the contents of the label switching table (label forwarding information base or LFIB) • Data plane has a simple forwarding engine To better understand the inner workings of MPLS, its two major components should be clarified: n Control plane, which takes care of the routing information exchange and the label exchange between adjacent devices n Data plane, which takes care of forwarding either based on destination addresses or labels. There is a large number of different routing protocols such as OSPF, IGRP, EIGRP, IS-IS, RIP, BGP, etc. that can be used in the control plane. The control plane also requires protocols such as TDP (MPLS), LDP (MPLS), BGP (MPLS/VPNs), RSVP (Traffic Engineering), CR-LDP (Traffic Engineering), etc. to exchange labels. The data plane however, is a simple label-based forwarding engine that is independent of the type of routing protocol or label exchange protocol. A Label Forwarding Information Base (LFIB) is used to forward packets based on labels. The LFIB table is populated by the control plane. 23-8 World Wide Training Word Templates v1 Copyright 1999, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS Architecture MPLS Architecture • Router’s functionality is divided into two major parts: control plane and data plane Data plane Control plane OSPF: 10.0.0.0/8 LDP: 10.0.0.0/8 Label 17 OSPF LDP LFIB LDP: 10.0.0.0/8 Label 4 OSPF: 10.0.0.0/8 4à17 Labeled packet Label 4 Labeled packet Label 17 A simple MPLS-enabled network implements destination-based forwarding that uses labels to make forwarding decisions. A layer-3 routing protocol is still needed to propagate layer-3 routing information. A label exchange mechanism is simply an add-on to propagate labels that are used for layer-3 destinations. The example in the figure illustrates the two components of the control plane: n OSPF that receives and forwards IP network 10.0.0.0/8, and places that prefix into the routing table. n LDP that receives label 17 to be used for packets with a destination address 10.x.x.x. A local label 4 is generated and sent to upstream neighbors so these neighbors can label packets with the appropriate label. LDP inserts an entry into the Data Plane’s LFIB table where label 4 is mapped to label 17. The data plane then forwards all packets with label 4 through the appropriate interfaces and replaces the label with label 17. Copyright 1999, Cisco Systems, Inc. Release Date: 2/1/99 23-9 © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS Modes of Operation MPLS Modes of Operation • MPLS technology is designed to be Layer-1 and Layer-2 independent • MPLS uses a 32-bit label field which is inserted between Layer-2 and Layer-3 headers (frame mode) • MPLS over ATM uses the ATM header as the label (cell mode) MPLS is designed for use on virtually any media and layer-2 encapsulation. Most layer-2 encapsulations are frame-based and MPLS simply inserts a 32-bit label between the layer-2 and layer-3 headers (“frame-mode” MPLS). ATM is a special case where fixed-length cells are used and a label cannot be inserted on every cell. MPLS uses the VPI/VCI fields in the ATM header as a label (“cell-mode” MPLS). 23-10 World Wide Training Word Templates v1 Copyright 1999, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS IP over MPLS Label Format Label Format MPLS uses a 32-bit label field that contains the following information: • 20-bit label • 3-bit experimental field • 1-bit bottom-of-stack indicator • 8-bit time-to-live field (TTL) LABEL EXP S TTL 0 19 22 23 31 20 24 A 32-bit label contains the following fields: n 20-bit label: the actual label n 3-bit experimental field: used to define a class of service (i.e. IP precedence) n Bottom-of-stack bit: MPLS allows multiple labels to be inserted; this bit is used to determine if this is the last label in the packet n 8-bit time-to-live (TTL) field: has the same purpose as the TTL field in the IP header [...]... DSCP MPLS exp IP Domain class-map match-any MPLS5 class-map match-any MPLS5 match mpls exp 5 match match ip precedence 5 match ip precedence 5 class-map match-any MPLS4 class-map match-any MPLS4 match mpls exp 4 match mpls exp match ip precedence 4 match class-map match-any MPLS3 class-map match-any MPLS3 match mpls exp 3 match mpls exp match ip precedence 3 match ip precedence 3 ! ! policy-map MPLS2 QoS... policy-map IP+ MPLS policy -map class Gold class bandwidth 3000 bandwidth class Silver class Silver bandwidth 1000 bandwidth 1000 ! ! Interface Ethernet0/0 Interface Ethernet0/0 ip address 10.1.1.1 255.255.255.0 ip address 10.1.1.1 255.255.255.0 mpls ip mpls ip service-policy output IP+ MPLS service-policy output IP+ MPLS ! ! © 2001, Cisco Systems, Inc IP QoS IP over MPLS Classification based on MPLS experimental... 23-19 MPLS QoS • MPLS uses labels to make a forwarding decision • The MPLS label is inserted between Layer-2 (frame) and Layer-3 (IP packet) headers • All Layer-3 information becomes invisible to routers in an MPLS domain • Classification in MPLS- enabled networks can be performed on: • MPLS experimental bits • MPLS labels (future enhancement) © 2001, Cisco Systems, Inc IP QoS IP over MPLS Frame-mode MPLS. .. Implementation IP precedence DSCP IP Domain class-map EF class-map EF match ip dscp ef match ip dscp ef class-map AF1LD class-map AF1LD match ip dscp af11 af12 match ip dscp af11 af12 class-map AF1HD class-map AF1HD match ip dscp af13 match ip dscp af13 ! ! policy-map DSCP2prec policy-map DSCP2prec class EF class EF set ip precedence 5 set ip precedence 5 class AF1LD class AF1LD set ip precedence 4 set ip precedence... AF1HD class AF1HD set ip precedence 3 set ip precedence 3 ! ! © 2001, Cisco Systems, Inc MPLS exp MPLS Domain interface Serial5/1/0 interface Serial5/1/0 service-policy input DSCP2prec service-policy ! ! IP QoS IP over MPLS The first part of the configuration shows how DSCP is translated to IP precedence on ingress into the MPLS network IP precedence is then automatically copied into MPLS experimental... Label Assignment Frame Header IP Payload IP precedece MPLS exp Frame Header LABEL IP Payload • An MPLS label has a three-bit experimental field • Cisco routers automatically copy IP precedence bits into the MPLS experimental bits • The Modular QoS CLI can be used to classify labeled packets based on their MPLS experimental bits © 2001, Cisco Systems, Inc IP QoS IP over MPLS The figure illustrates the... Copyright © 1999, Cisco Systems, Inc MPLS Translation Case Study IP Domain MPLS Domain • IP domain is using the DiffServ model: - EF – Class Premium AF1 – Class Gold AF2 – Class Silver Default – Best effort class • Translate IP DSCP values to and from MPLS experimental bits to achieve a similar result in the MPLS domain © 2001, Cisco Systems, Inc IP QoS IP over MPLS The QoS design in the case study... set -mpls- exp-tr 5 exceed setmpls -exp-tr 0 mpls- exp-tr 0 rate-limit output 64000 2000 2000 conform set -mpls- exp-tr 5 exceed set rate-limit output 64000 2000 2000 conform set -mpls- exp-tr 5 exceed setmpls -exp-tr 0 mpls- exp-tr 0 ! ! © 2001, Cisco Systems, Inc IP QoS IP over MPLS CAR also supports a special rate-limit access list that can match labeled packets based on their MPLS experimental values The... Router(config-cmap)# match mpls experimental exp • Classifies packets based on MPLS experimental bits class-map match-any Gold class-map match-any Gold match ip precedence 3 4 match ip precedence 3 4 match mpls experimental 3 4 match mpls experimental 3 4 ! ! class-map match-any Silver class-map match-any Silver match ip precedence 1 2 match ip precedence 1 2 match mpls experimental 1 2 match mpls experimental... Switch Router (LSR) primarily forwards labeled packets (label swapping) • Edge LSR primarily labels IP packets and forwards them into the MPLS domain, or removes labels and forwards IP packets out of the MPLS domain © 2001, Cisco Systems, Inc IP QoS IP over MPLS Before proceeding with a detailed description of MPLS, some of the terminology that is used in this course is presented: n Label Switch Router (LSR): . 23-5 © 2001, Cisco Systems, Inc. IP QoS IP over MPLS MPLS vs. IP- over- ATM MPLS vs. IP- over- ATM • Layer-2 devices are IP- aware and run a routing protocol •. Systems, Inc. IP QoS IP over MPLS MPLS Modes of Operation MPLS Modes of Operation • MPLS technology is designed to be Layer-1 and Layer-2 independent • MPLS uses