MPLS Design

Figure 513 Backbone Carrier Supporting an ISP

M *usrior rt)u 0f inlwmation (IPv4 NLflJs I6GP-* j In order to solve the scalability problem, the backbone carrier is configured so that it allows only internal routes of the customer carrier (IGP routes) to be exchanged between the CE routers of the customer carrier and the PE routers of the backbone carrier. MPLS is enabled on the interface between the CE router of the customer carrier and the PE router of the backbone carrier. Internal routes go to any of the routers within the ISP, and...

OSPF Unequal Cost Load Balancing

Open Shortest Path First (OSPF) uses the cost metric to calculate the best path to a destination network. The path cost is the cumulative sum of the costs assigned to all interfaces that forward traffic along the path to the destination. OSPF calculates the cost based on the link's bandwidth. In general, the path cost in routers is calculated using the formula 108 bandwidth (in bps). OSPF defaults to equal-cost load balancing. In other words, it load-shares across equal-cost links only. In...

Advanced MPLS Design and Implementation

An in-depth guide to understanding advanced MPLS implementation, including packet-based VPNs, ATM-based VPNs, traffic engineering, and quality of service Who Should Read This Book Scope and Definition Command Conventions Illustration Iconography A New Forwarding Paradigm What Is MPLS Summary WAN Technologies and MPLS Inside the Cloud Layer 3 Routing Label Switching Integration of IP and ATM Challenges Faced by Service Providers Summary MPLS Architecture MPLS Operation MPLS Node Architecture...

Appendix A Mpls Command Reference

This MPLS command reference provides tables that document the commonly used MPLS commands. Cisco's prestandard equivalent tag-switching commands are provided, along with their MPLS counterparts. Sample usage of many of these commands can be found in the case studies and examples throughout this book. For sample usage of the remaining commands listed here, refer to the IOS Command Reference and Configuration Guide. These documents are available on Cisco's documentation CD-ROM and on Cisco...

Conventional IP VPNs

Many carriers provide a managed IP services offering that basically lets customers hook up their CPE IP routers to a service provider's private IP backbone. Most IP service providers run an IP network over a Layer 2 infrastructure such as an ATM or Frame Relay network. An example of a conventional IP VPN is shown in Figure 4-9. Figure 4-9. Conventional IP Router-Based VPN Network Figure 4-9. Conventional IP Router-Based VPN Network The service provider typically configures multiple routing...

Packet Based Mpls Vpns

This chapter covers the following topics MPLS VPN Operation MPLS Virtual Private Networks can be built over existing Layer 2 infrastructures. This section details the various MPLS VPN building blocks and the interaction between the various MPLS elements. This section also explains VPN route target communities, distribution of VPN routing information, and MPLS forwarding. The various packet-based MPLS LSR commands used to build VPN networks are explained. These commands are later exemplified in...

Layer 3 Routing Design

MPLS uses link-state routing protocols such as OSPF and IS-IS to determine the routes for IP traffic and LVCs. LSRs run IP routing protocols in the same way that regular IP routers do. Designing IP routing in an MPLS network is almost exactly the same process as designing IP routing for an ordinary IP network. The network can be depicted in a logical topology, and a routing topology can be ascertained. By looking at the routing topology, you can divide the network into areas, design route...

Configuration for AS1 EBGP1

The following is the configuration used for Exterior Border Gateway Protocol router 1 (EBGP1). EBGP1 is configured with the redistribute connected subnets command and interfaces with AS2. interface LoopbackO ip address 10.0.0.4 255.255.255.255 interface Ethernet0 0 description EBGP1 to P1 ip address 10.2.1.2 255.255.255.0 tag-switching ip interface Serial0 0 description EBGP1 to EBGP2 ip address 12.0.0.1 255.255.255.252 router ospf 1 log-adjacency-changes redistribute connected subnets network...

Optimized Rerouting

Fast rerouting can result in suboptimal traffic-engineered paths. The key is to dynamically respond to failure as well as to new or restored paths. Thus, when a failure is detected, it is necessary to also notify the headend of the LSP tunnel. The headend can then compute a more optimal path. Traffic can then be diverted to the new LSP tunnel. This can be done without further disruption. Often missing from Layer 2 networks is a feature called bridge-and-roll or make-before-break. This is the...

Multiprotocol Lambda Switching

Multiprotocol Lambda Switching (MP .S) is the optical analogy of MPLS. The MPLS control plane performs all crucial control functions for MPLS data networks. MPLS RSVP-TE extensions or CR-LSDP extensions can be applied to optical networks to unify the control plane for optical network elements. MP .S approaches the design of control planes for OXC switches and other integrated multifunctional optical switches that leverage existing control-plane techniques developed for MPLS traffic engineering....

ATM Quality of Service QoS

Traffic management is the key feature of ATM that distinguishes it from current networking protocols and makes it suitable for deployment in high-speed networks and for providing performance guarantees in an integrated environment. ATM supports QoS guarantees composed of traffic contract, traffic shaping, and traffic policing. A traffic contract specifies an envelope that describes the intended data flow. This envelope specifies values for peak bandwidth, average sustained bandwidth, and burst...

Packet Prioritization

IP packets can be classified according to their source address, destination address, port, protocol identification, or class of service field. Packet classification is important, because a packet's priority is determined by how it is classified or marked. A packet's priority affects how the packet is treated during periods of congestion. For example, service providers have Service-Level Agreements (SLAs) with customers. The agreement specifies how much traffic the service provider has agreed to...

Assured Forwarding AF PHB

The DSCP marking of AF packets specifies an AF class and drop preference for IP packets. Packets with different drop preferences within the same AF class are dropped based on the their relative drop precedence values within the AF class. RFC 2587 recommends 12 AF PHBs representing four AF classes with three drop-preference levels in each. The Assured Forwarding PHB defines a method by which BAs can be given different forwarding assurances. The AFxy PHB defines four classes AF1y, AF2y, AF3y, and...

Service Policy Configuration

A service policy is configured using the policy-map command to specify a service policy name. The traffic class is associated with the service policy with the class command. The QoS policies for the service policy are defined in policy map submode. The QoS policies that can be applied in the service policy in policy map submode are detailed in this section. The policy-map syntax is as follows policy-map policy-name no policy-map policy-name The class command syntax is as follows class...

Optical Add Drop Multiplexer

The OADM is the optical subsystem that facilitates the add and drop of wavelengths into the physical fiber without having to regenerate all the WDM channels. Rather than combining or separating all wavelengths, the OADM can remove some while passing others on. No conversion of the signal from optical to electrical takes place. The system maintains each connection as sequential ports and performs manipulations on them. The wavelengths or channels to be added or dropped can be either preassigned...

Forwarding Equivalency Class

Forwarding Equivalency Class (FEC) is a set of Layer 3 packets that are forwarded in the same manner over the same path with the same forwarding treatment. While assigning a packet to an FEC, the router might look at the IP header and also some other information, such as the interface on which this packet arrived. FECs might provide a coarse or fine forwarding granularity based on the amount of information considered for setting the equivalence. A set of unicast packets whose Layer 3...

Integration of IP and ATM

The early proponents and developers of ATM envisioned it to be a ubiquitous technology, spanning the desktop, LAN, and WAN. Today, few people still cling to that vision. Instead, IP has proliferated with the explosion of the Internet. The concept of IP over anything has taken precedence over the focus on forcing ATM to behave like a legacy LAN protocol. ATM on the LAN, driven by LANE (LAN Emulation), classical IP over ATM, and MPOA (multiprotocol over ATM), has seen limited growth and has been...

Figure 210 Atm Uni and NNI Interfaces

CPS CPS ATM' Asynchronous Transfer Wade isyw ATM' Asynchronous Transfer Wade isyw A public UNI connects a private ATM switch to a public ATM service provider's network. A private UNI connects ATM users to the ATM switch. The term trunk is used to indicate the ATM link between carrier switches, and the term line is used to indicate the link between the customer equipment to the carrier's closest point of presence (POP) ATM switch. UNI ATM headers are typically used between the CPE and the...

Dense Wavelength Division Multiplexing

Conventional fiber-optic systems use a single wavelength or color injected by an optical transmitter that is a light-emitting diode (LED) in the case of multimode fiber (MMF) or a laser diode in the case of single-mode fiber (SMF). Laser diodes or LEDs perform an electrical-to-optical (EO) conversion of the electrical signal. The light is injected at a precise angle into the core of the fiber-optic cable using a lens, which has a higher refractive index than the cladding. Light pulses are...

Optical UNI

The Optical Internetworking Forum (OIF) is the standards body that is developing an Optical User Network Interface (O-UNI), which provides an interface between optical clients and an optical network. The O-UNI defines a link for communicating control, signaling, and data packets between the optical client (such as an IP router) and the adjacent optical transport-networking device (such as an OXC). The O-UNI was created so that carriers could offer a simple, open, external interface for...

MPLS Backbone Link Sizing

The following steps detail the procedures involved with MPLS backbone link sizing Step 2. Estimate traffic from each point of presence. Step 3. Estimate the unidirectional traffic matrix. Step 4. Estimate the bidirectional traffic matrix. Step 5. Design the backbone trunk topology. Step 6. Calculate estimated link bandwidths. The first step in MPLS network design is to select the size, type, and layout of the PoPs according to the considerations described in the previous section. The edge PoPs...

Table 21a DSLevel Hierarchy

An example of a circuit-switched network from a customer's perspective is shown in Figure 2-1. This topology is also referred to as a point-to-point line or nailed circuit. Typically, such lines are leased from a local exchange carrier (LEC) or interexchange carrier (IXC) and are also referred to as leased or private lines. One leased line is required for each of the remote sites to connect to the headquarters at the central site. Figure 2-1. Leased Lines from a Customer Perspective Figure 2-1....

J 10000 200

This means that only 54 LSRs can be used in the network. NOTE Using multiple areas can have major disadvantages in ATM MPLS networks without VC merge. The preceding examples indicate that ATM LSRs without VC merge typically can't be used in networks larger than a few hundred nodes. A workaround is to use the same switches with MPLS-over-PVCs instead of ATM MPLS. Design Calculations for ATM LSRs with VC Merge With VC merge, the LVCs to each destination are merged at each ATM LSR. This means that...

Benefits of MPLS

Label-based switching methods allow routers and MPLS-enabled ATM switches to make forwarding decisions based on the contents of a simple label, rather than by performing a complex route lookup based on destination IP address. This technique brings many benefits to IP-based networks VPNs Using MPLS, service providers can create Layer 3 VPNs across their backbone network for multiple customers, using a common infrastructure, without the need for encryption or end-user applications. Traffic...

Virtual Connections

Each ATM cell, whether sent at the UNI or the NNI, contains information that identifies the virtual connection to which it belongs. That identification has two parts a virtual channel identifier and a virtual path identifier. Both the VCI and VPI are used at the ATM layer. The virtual channels, with their VCIs, and the virtual paths, with their VPIs, are contained within the physical transmission path, as shown in Figure 2-11. Figure 2-12 shows ATM virtual circuits from a customer perspective....

Data Link Connection Identifier DLCI

A data-link connection identifier (DLCI) identifies the Frame Relay PVC. Frames are routed through one or more virtual circuits identified by DLCIs. Each DLCI has a permanently configured switching path to a certain destination. Thus, by having a system with several DLCIs configured, you can communicate simultaneously with several different sites. The User-Network Interface (UNI) provides the demarcation between the FRAD and the Frame Relay network. The combination of the UNI and the DLCI...

Label Switched Router LSR

The LSR is a device that implements the MPLS control and forwarding components. The LSR forwards a packet based on the value of a label encapsulated in the packet. The LSR can also forward native Layer 3 packets. LSRs are MPLS-enabled routers or MPLS-enabled ATM switches that use labels to forward traffic. Packet-based LSRs can easily be built by loading an IOS image with the MPLS feature set on a conventional router. ATM MPLS LSRs are built using an ATM switch with integrated MPLS software or...

Unified Control Plane

MPLS operates on a forwarding plane and a control plane. The control plane for MPLS can be extended to the optical layer. This forms the basis of the Unified Control Plane (UCP). Existing packet-oriented control planes, such as those used by MPLS, were designed to encompass devices that could recognize packet and or cell boundaries. The header contents are processed in order to create the LSP and make forwarding decisions. However, within OTNs, devices and their constituent protocols make their...

Circuit Switching and TDM

Time-division multiplexing combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel. Within T-carrier systems, such as T1 E1 and T3 E3, TDM combines pulse code modulated (PCM) streams created for each conversation or data stream. TDM circuits such as T1 E1 or T3 E3 lines can be used for voice as well as data. PCM is used to encode analog signals into digital format. Voice calls need...

What Is MPLS

MPLS is an improved method for forwarding packets through a network using information contained in labels attached to IP packets. The labels are inserted between the Layer 3 header and the Layer 2 header in the case of frame-based Layer 2 technologies, and they are contained in the virtual path identifier (VPI) and virtual channel identifier (VCI) fields in the case of cell-based technologies such as ATM. MPLS combines Layer 2 switching technologies with Layer 3 routing technologies. The...

Per Hop Behavior PHB

As shown in Figure 8-6, network elements or hops along the path examine the value of the DSCP field and determine the QoS required by the packet. This is known as aper-hop behavior (PHB). Each network element has a table that maps the DSCP found in a packet to the PHB that determines how the packet is treated. The DSCP is a number or value carried in the packet, and PHBs are well-specified behaviors that apply to packets. A collection of packets that have the same DSCP value in them, and...

Conventional Layer 3 Routing Versus MPLS

As Layer 3 packets are forwarded from one router to the next, each router makes an independent forwarding decision for that packet. Each router analyzes the destination Layer 3 address in the packet's header and runs a network layer routing algorithm. Each router independently chooses a next hop for the packet based on its analysis of the packet's header and the results of running the routing algorithm. Forwarding decisions are the result of two functions Classification of Layer 3 packets into...

Traffic Class Configuration

The class-map command is used to create a traffic class. In order to create a traffic class containing match criteria, the class-map command is used to specify the traffic class name, and a match command is used in class map configuration mode. class-map match-any match-all class-name no class-map match-any match-all class-name The class-map match-all command is used when all of the match criteria in the traffic class must be met in order for a packet to match the specified traffic class. The...

MPLS Redundancy Using HSRP

HSRP provides network redundancy in a way that ensures that user traffic immediately and transparently recovers from first-hop failures in network edge devices and access circuits. By sharing an IP address and a MAC (Layer 2) address, two or more routers can act as a single virtual router to the hosts on a LAN. The members of the router group continually exchange status messages by detecting when a router goes down. This HSRP group consists of an active router and a standby router to replace...

Advantages of MPLS Traffic Engineering

MPLS traffic engineering features allow an MPLS backbone to replicate and expand upon the traffic engineering capabilities of Layer 2 ATM and Frame Relay networks. Traffic engineering is essential for service provider and Internet service provider backbones. Both backbones must support a high use of transmission capacity, and the networks must be very resilient so that they can withstand link or node failures. The following are the advantages of MPLS traffic engineering With MPLS, traffic...

IP Precedence

The IntServ RSVP per-flow approach to QoS described in the preceding section is clearly not scalable and leads to complexity of implementation. IP precedence defined by the IETF has simplified the approach to IP QoS by adopting an aggregate model for flows by classifying various flows into aggregated classes and providing the appropriate QoS for the classified flows. Packets are classified at the edge of the network into one of eight different classes. This is accomplished by setting three...

San Diego PE Configuration

CEF switching is a prerequisite for label switching Define VPN Routing instance vrfl (customer A) rd 100 1 Configure the Route Distinguisher for vrfl route-target both 100 1 Configure import and export route-targets for vrf1 Define VPN Routing instance vrf3 (customer C) rd 100 3 Configure the Route Distinguisher for vrf3 route-target both 100 3 Configure import and export route-targets for vrf3 interface loopback 0 ip address 10.10.3.1 255.255.255.255 Configure the PE loopback IP address...

Penultimate Hop Popping

The packet-based LSR operation described in the preceding section has certain drawbacks associated with the double lookup performed at the egress LSR4. LSR4 would need to examine the label stack and look up the label in its LFIB, only to realize that it needs to be popped. It then would need to perform a Layer 3 lookup in its global or VPN-specific routing table in order to correctly forward the packet to the external next-hop router. The double lookup at LSR4 can result in a performance...

Mpls Vpn Support of QoS

A VPN is defined as a closed user group sharing a public network infrastructure with a set of administrative policies that control both connectivity and QoS among sites. The various MPLS QoS CoSs should be available on a per-VPN basis. Applications should receive various CoSs within the VPN. For example, real-time applications such as VoIP could receive a preferential CoS versus a file transfer. Two models are used to describe QoS in the VPN context the pipe model and the hose model. In the...

Figure B1B VSI Controllers

The MPLS control software is implemented in the LSC. Other VSI controllers may be software running on the switch control card. In the case of the BPX 8650 and MGX 8850, AutoRoute software, which controls PVCs, runs on the switch control card. PNNI control may be added to the BPX 8650 as a separate controller on the Service Expansion Shelf (SES). The LS1010 and 8540 MSR implement functionality similar to the VSI using internal software interfaces. To ensure that the control planes can act...

Figure 510 Route Reflector Design

When considered as a whole, the route reflector and its clients are called a cluster. Other IBGP peers of the route reflector that are not clients are called nonclients. An AS can have more than one route reflector. When an AS has more than one route reflector, each route reflector treats other route reflectors as normal IBGP speakers. There can be more than one route reflector in a cluster, and there can be more than one cluster in an AS. The BGP configuration for the PE routers in Figure 5-10...

BGP Route Reflectors

BGP requires that all of the IBGP speakers be fully meshed. However, this requirement does not scale when there are many IBGP speakers. A BGP speaker does not advertise a route learned from another IBGP speaker to a third IBGP speaker. Route reflectors ease this limitation and allow a router to advertise or reflect IBGP-learned routes to other IBGP speakers, thereby reducing the number of IBGP peers within an Autonomous System (AS). BGP confederations can be used to reduce the IBGP full mesh as...

Figure 814 Example of Mpls Vpn QoS Hose Model

The service provider also supplies VPN1 with certain guarantees of up to 45 Mbps for traffic sent by site 2 and site 3 to site 1 (site 1 ECR 45 Mbps). This traffic could be directed to site 1 from site 2 or site 3 or distributed in an arbitrary way between site 2 and site 3 and sent to site 1. In VPN2, the service provider supplies certain guarantees of up to 20 Mbps for traffic sent by site 1 to site 2 (site 1 ICR 20 Mbps). Site 1 also has an ECR of 20 Mbps, which means that site 2 can send...