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Page 1: EE11--E2 (CFA)E2 (CFA)210.212.144.213/course_material/e1e2/cfa/E1-E2 PPT/Chapter05 MP… · Basic MPLS Concepts MPLS is a new forwarding mechanism in which packets are forwarded based

E1E1--E2 (CFA)E2 (CFA)

For internal circulation of BSNL only

MPLSMPLS--VPNVPN

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MPLSMPLS

For internal circulation of BSNL only

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BASIC CONCEPTS OF MPLS

CONTENTS

Drawbacks of Traditional IP Forwarding

Basic MPLS Concepts

MPLS versus IP over ATMMPLS versus IP over ATM

Traffic Engineering with MPLS

MPLS Architecture

MPLS Labels

Label Switch Routers

For internal circulation of BSNL only

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Routing protocols are used to distribute Layer 3 routing

information.

Forwarding is based on the destination address only.

Drawbacks of Traditional IP Forwarding

Routing lookups are performed on every hop.

For internal circulation of BSNL only

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Drawbacks of Traditional IP Forwarding

Traditional IP Forwarding

Every router may need full Internet routing

information

For internal circulation of BSNL only

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Drawbacks of Traditional IP Forwarding

Traditional IP Forwarding

Every router may need full Internet routing information (more than

100,000 routes).Destination-based routing lookup is needed on every hop.

For internal circulation of BSNL only

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Drawbacks of Traditional IP Forwarding

(Cont.)

IP over ATM

Layer 2 devices have no knowledge of Layer 3 routing

information—virtual circuits must be manually established.

For internal circulation of BSNL only

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Drawbacks of Traditional IP Forwarding

(Cont.)

IP over ATM

Layer 2 devices have no knowledge of Layer 3 routing information—

virtual circuits must be manually established.

Layer 2 topology may be different from Layer 3 topology, resulting in

suboptimal paths and link use.

Even if the two topologies overlap, the hub-and-spoke topology is

usually used because of easier management.

For internal circulation of BSNL only

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Drawbacks of Traditional IP Forwarding

(Cont.) Traffic Engineering

Most traffic goes between large sites A and B, and uses only the primary

link.

Destination-based routing does not provide any mechanism for load

balancing across unequal paths.

Policy-based routing can be used to forward packets based on other

parameters, but this is not a scalable solution.

For internal circulation of BSNL only

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Basic MPLS Concepts

MPLS is a new forwarding 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, such as Labels can also correspond to other parameters, such as

QoS or source address.

MPLS was designed to support forwarding of other

protocols as well.

For internal circulation of BSNL only

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Basic MPLS Concepts Example

For internal circulation of BSNL only

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Basic MPLS Concepts Example

Only edge routers must perform a routing lookup.

For internal circulation of BSNL only

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Basic MPLS Concepts

Only edge routers must perform a routing lookup.

Core routers switch packets based on simple label lookups and swap labels.

For internal circulation of BSNL only

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MPLS versus IP over ATM

Layer 2 devices are IP-aware and run a routing protocol.

For internal circulation of BSNL only

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MPLS Versus IP over ATM

Layer 2 devices are IP-aware and run a routing protocol.

There is no need to manually establish virtual circuits.

For internal circulation of BSNL only

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MPLS Versus 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.

For internal circulation of BSNL only

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Traffic Engineering with MPLS

Traffic can be forwarded based on other parameters (QoS,

source, ...).

Load sharing across unequal paths can be achieved.

For internal circulation of BSNL only

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MPLS Architecture

• MPLS has two major components:

• Control plane: Exchanges Layer 3 routing

information and labels

• Data plane: Forwards packets based on

labelslabels

Control plane contains complex mechanisms to

exchange routing information, such as OSPF,

EIGRP, IS-IS, and BGP, and to exchange labels,

such as TDP, LDP, BGP, and RSVP.

Data plane has a simple forwarding engine.

For internal circulation of BSNL only

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MPLS Architecture

Router functionality is divided into two major

parts: control plane and data plane

For internal circulation of BSNL only

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MPLS Architecture

Router functionality is divided into two major parts: control plane

and data plane

For internal circulation of BSNL only

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MPLS Architecture

Router functionality is divided into two major parts:

control plane and data plane

For internal circulation of BSNL only

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MPLS Architecture

Router functionality is divided into two major parts: control plane

and data plane

For internal circulation of BSNL only

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MPLS Architecture

Router functionality is divided into two major parts: control plane

and data plane

For internal circulation of BSNL only

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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

For internal circulation of BSNL only

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MPLS Labels 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 TTL field

For internal circulation of BSNL only

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MPLS Label Stack

Protocol identifier in a Layer 2 header specifies that

the payload starts with a label (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.

For internal circulation of BSNL only

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MPLS Label Stack

Usually only one label is assigned to a packet.

The following scenarios may produce more than one

label:

– MPLS VPNs (two labels: The top label points to the egress router

and the second label identifies the VPN.)and the second label identifies the VPN.)

– MPLS TE (two or more labels: The top label points to the

endpoint of the traffic engineering tunnel and the second label

points to the destination.)

– MPLS VPNs combined with MPLS TE (three or more labels.)

For internal circulation of BSNL only

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MPLS Labels

For internal circulation of BSNL only

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MPLS Labels

For internal circulation of BSNL only

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Label Switch Routers

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.

For internal circulation of BSNL only

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Label Switch Routers

Architecture of LSRs

•LSRs, regardless of the type, perform these functions:

Exchange routing information

Exchange labels

Forward packetsForward packets

– The first two functions are part of the control plane.

– The last function is part of the data plane.

For internal circulation of BSNL only

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Label Switch Routers

Architecture of LSRs

For internal circulation of BSNL only

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Label Switch Routers

Architecture of Edge LSRs

For internal circulation of BSNL only

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Terminology

Label: A label is an identifier, which indicates the path a

packet, should traverse. Label is carried along with the packet.

The receiving router examines the packet for its label content to

determine the next hop. Once a packet has been labeled, the

rest of the journey of the packet through the backbone is based

on label switching. Since every intermediate router has to lookon label switching. Since every intermediate router has to look

in to the label for routing the decision making at the level of

router becomes fast.

Label Creation: Every entry in routing table (build by using any

IGP protocol) is assigned a unique 20-bit label.

For internal circulation of BSNL only

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Terminology

SWAP: Every incoming label is replaced by a new outgoing

label (As per the path to be followed) and the packet is

forwarded along the path associated with the new label.

PUSH: A new label is pushed on top of the packet, effectively

"encapsulating" the original IP packet in a layer of MPLS.

POP: The label is removed from the packet effectively "de-POP: The label is removed from the packet effectively "de-

encapsulating". If the popped label was the last on the label

stack, the packet "leaves" the MPLS tunnel.

LER: A router that operates at the edge of the access

network and MPLS network LER performs the PUSH and

POP functions and is also the interface between access and

MPLS network, commonly know as Edge router.

For internal circulation of BSNL only

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Terminology

LSR: An LSR is a high-speed router device in the core of

an MPLS network, normally called Core routers. These

routers perform swapping functions and participate in the

establishment of Label Switch Path (LSP)

Ingress / Egress Routers: The routers receiving theIngress / Egress Routers: The routers receiving the

incoming traffic or performing the first PUSH function are

ingress routers and routers receiving the terminating

traffic or performing the POP function are Egress

routers. The same router performs both functionality i.e.

Ingress and Egress. The routers performing these

functions are LER.

For internal circulation of BSNL only

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Terminology

FEC: The forward equivalence class (FEC) is a

representation of a group of packets that share the same

requirements for their transport. All packets in such a

group are provided the same treatment en route to the

destination. As opposed to conventional IP forwarding, indestination. As opposed to conventional IP forwarding, in

MPLS, the assignment of a particular packet to a

particular FEC is done just once, as the packet enters

the network at the edge router.

For internal circulation of BSNL only

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MPLS functions

MPLS performs following functions

Specifies mechanisms to manage traffic flow of various

granularities, such as flows between different hardware,

machines, or even flows between different applications.

MPLS remains independent of the Layer-2 & layer-3 protocols.

Meaning thereby that label encapsulating the data packetMeaning thereby that label encapsulating the data packet

does not depend upon layer 3 /layer 2 protocol of data. This

justifies the name as multi protocol label switching.

For internal circulation of BSNL only

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MPLS functions contd…

Provides a means to map IP addresses to simple, fixed-length

labels used by different packet-forwarding and packet-

switching technologies

Interfaces to existing routing protocols such as resource Interfaces to existing routing protocols such as resource

reservation protocol (RSVP) and open shortest path first

(OSPF).

Supports the IP, ATM, and frame- relay Layer-2 protocols.

For internal circulation of BSNL only

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Label Distribution Protocol

(LDP)

The LDP is a protocol for the distribution of label

information to LSRs in a MPLS networks. It is used to

map FECs to labels, which, in turn, create LSP.map FECs to labels, which, in turn, create LSP.

LDP sessions are established between LDP peers in the

MPLS network (not necessarily adjacent).

For internal circulation of BSNL only

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MPLS Operation

The following steps must be taken for a data packet to

travel through an MPLS domain:

Label creation and distribution

Table creation at each routerTable creation at each router

Label-switched path creation

Label insertion/table lookup

Packet forwarding

For internal circulation of BSNL only

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MPLS Applications

MPLS addresses today’s network backbone

requirements effectively by providing a standards-based

solution that accomplishes the following:

Improves packet-forwarding performance in the network.

MPLS enhances and simplifies packet forwardingMPLS enhances and simplifies packet forwarding

through routers using Layer-2 switching paradigms.

MPLS is simple which allows for easy implementation.

MPLS increases network performance because it

enables routing by switching at wire line speeds.

Supports QoS and CoS for service differentiation.

For internal circulation of BSNL only

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MPLS Applications

MPLS uses traffic-engineered path setup and helps

achieve service-level guarantees.

MPLS incorporates provisions for constraint-based and

explicit path setup.

Supports network scalability.

MPLS can reuse existing router/ATM switch hardware,MPLS can reuse existing router/ATM switch hardware,

effectively joining the two disparate networks.

Builds interoperable networks

MPLS is a standards-based solution.

MPLS helps build scalable VPNs with traffic-engineering

capability.

For internal circulation of BSNL only

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Advantages of MPLS over

other technologies

BSNL's primary objectives in setting up the BGP/MPLS

VPN network are:

Provide a diversified range of services (Layer 2, Layer 3

and Dial up VPNs) to meet the requirements of the entire

spectrum of customers from Small and Medium to Largespectrum of customers from Small and Medium to Large

business enterprises and financial institutions.

Make the service very simple for customers to use even

if they lack experience in IP routing.

Make the service very scalable and flexible to facilitate

large-scale deployment.

For internal circulation of BSNL only

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Advantages of MPLS over

other technologies

Provide a reliable and amenable service.

Offering SLA to customers.

Capable of meeting a wide range of customer

requirements, including security, quality of Service

(QOS) and any-to-any connectivity.(QOS) and any-to-any connectivity.

Capable of offering fully managed services to

customers.

Allow BSNL to introduce additional services such as

bandwidth on demand etc over the same network.

For internal circulation of BSNL only

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MPLSMPLS--VPNVPN

For internal circulation of BSNL only

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Overview

Traditional Router-Based Networks

Virtual Private Networks

VPN Terminology

MPLS VPN ArchitectureMPLS VPN Architecture

MPLS VPN Routing

MPLS VPN Label Propagation

For internal circulation of BSNL only

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Traditional Router-Based

Networks

Traditional router-based networks connect customer

sites through routers connected via dedicated point-to-

point links.

For internal circulation of BSNL only

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Virtual Private Networks

VPNs replace dedicated point-to-point links with emulatedpoint-to-point links sharing common infrastructure.

Customers use VPNs primarily to reduce their operationalcosts.

For internal circulation of BSNL only

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VPN Terminology

For internal circulation of BSNL only

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VPN Implementation

Technologies

VPN services can be based on two major models:

Overlay VPNs, in which the service provider provides virtual

point-to-point links between customer sites

Peer-to-peer VPNs, in which the service provider Peer-to-peer VPNs, in which the service provider

participates in the customer routing

For internal circulation of BSNL only

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Overlay VPNs

Service provider infrastructure appears as point-to-point

links to customer routes.

Routing protocols run directly between customer routers.

Service provider does not see customer routes and is

responsible only for providing point-to-point transport of

customer data.

For internal circulation of BSNL only

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Peer-to-Peer VPNs

For internal circulation of BSNL only

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Benefits of VPN Implementations

Overlay VPN:

–Well-known and is easy to implement.

– Service provider does not participate in customer routing.

– Customer network and service provider network are well

isolated.

Peer-to-peer VPN:

– Guarantees optimum routing between customer sites.

– Easier to provision an additional VPN.

– Only the sites are provisioned, not the links between them.

For internal circulation of BSNL only

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Drawbacks of VPN Implementations

Overlay VPN:

– Implementing optimum routing requires full mesh of

virtual circuits.

– Virtual circuits have to be provisioned manually.– Bandwidth must be provisioned on a site-to-sitebasis.basis.

– Overlay VPNs always incur encapsulation overhead.Peer-to-peer VPN:

– Service provider participates in customer routing.– Service provider becomes responsible for customerconvergence.

– PE routers carry all routes from all customers.– Service provider needs detailed IP routingknowledge.

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MPLS VPN Architecture

An MPLS VPN combines the best features of an

overlay VPN and a peer-to-peer VPN:

– PE routers participate in customer routing,

guaranteeing optimum routing between sites and

easy provisioning.

– PE routers carry a separate set of routes for each

customer (similar to the dedicated PE router

approach).

– Customers can use overlapping addresses.

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MPLS VPN Architecture -

Terminology

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PE Router Architecture

Backbone

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Propagation of Routing Information

Across the P-Network

Question: How will PE routers exchange customer routing information?

Answer #1: Run a dedicated Interior Gateway Protocol (IGP) for each customeracross the P-network.

This is the wrong answer for the following reasons:

The solution does not scale.

P routers carry all customer routes.

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Propagation of Routing Information

Across the P-Network

Question: How will PE routers exchange customer routing information?

Answer #2: Run a single routing protocol that will carry all customer routes inside the provider backbone.

Better answer, but still not good enough:

P routers carry all customer routes.

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Propagation of Routing Information

Across the P-Network

Question: How will PE routers exchange customer routing information?

Answer #3: Run a single routing protocol that will carry all customer routes between PE

routers. Use MPLS labels to exchange packets between PE routers.

The best answer:

� P routers do not carry customer routes; the solution is scalable.

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Propagation Routing Information

Across the P-Network

Question: Which protocol can be used to carry customer routes between PE routers?

Answer: The number of customer routes can be very large. BGP is the onlyrouting protocol that can scale to a very large number of routes.

Conclusion:BGP is used to exchange customer routes directly between PE routers.

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Propagation of Routing Information

Across the P-Network

Question: How will information about the overlapping subnets of two customers be propagated via a single routing protocol?

Answer: Extend the customer addresses to make them unique.

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Route Distinguishers

The 64-bit route distinguisher (RD) is prepended to an

IPv4 address to make it globally unique.

The resulting address is a VPNv4 address.

VPNv4 addresses are exchanged between PE routers

via BGP.

– BGP that supports address families other than IPv4

addresses is called Multiprotocol BGP (MP-BGP).

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Route Distinguishers

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Route Distinguishers

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Route Distinguishers

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Route Distinguishers

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Route Distinguishers

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Route Distinguishers

• The RD has no special meaning.

• Used only to make potentially overlapping IPv4

addresses globally unique.

• The RD could serve as a VPN identifier, but this design

could not support all topologies required by thecould not support all topologies required by the

customers.

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Route Targets - VoIP Service

Sample

Requirements:

All sites of one customer need to communicate.

Central sites of both customers need to communicate with VoIP gateways and other central sites.

Other sites from different customers do not communicate with each other.

A

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Route Targets Connectivity

Requirements

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Route Targets - Why Are They

Needed?

Some sites have to participate in more than

one VPN.

The RD cannot identify participation in more than one VPN.

RTs were introduced in the MPLS VPN architecture to

support complex VPN topologies.support complex VPN topologies.

– A different method is needed in which a set of identifiers can be

attached to a route.

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Route Targets - What Are They?

RTs are additional attributes attached to VPNv4 BGP

routes to indicate VPN membership.

Extended BGP communities are used to encode these

attributes.

– Extended communities carry the meaning of the – Extended communities carry the meaning of the

attribute together with its value.

Any number of RTs can be attached to a single route.

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Route Targets - How Do They Work?

Export RTs:

– Identifying VPN membership

– Appended to the customer route when it is converted

into a VPNv4 route

Import RTs:

– Associated with each virtual routing table

– Select routes to be inserted into the virtual routing

table

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MPLS VPN Routing - CE Router

Perspective

The CE routers run standard IP routing software and exchange

routing updates with the PE router.

• EBGP, OSPF, RIPv2, EIGRP, and static routes are

supported.

The PE router appears as another router in the C-network.

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MPLS VPN Routing

Overall Customer Perspective

To the customer, the PE routers appear as core

routers connected via a BGP backbone.

The usual BGP and IGP design rules apply.

The P routers are hidden from the customer.

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MPLS VPN Routing P Router

Perspective

P routers do not participate in MPLS VPN routing and do not

carry VPN routes.

P routers run backbone IGP with the PE routers and

exchange information about global subnets (core links and

loopbacks).

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MPLS VPN Routing PE Router

Perspective

� Exchange VPN routes with CE routers via per-VPN routing protocols

– Exchange VPNv4 routes with other PE routers via MP-IBGP sessions

PE routers:

� Exchange core routes with P routers and PE routers via core IGP

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Routing Tables on PE Routers

PE routers contain a number of routing tables:

– Global routing table, which contains core routes (filled with core

IGP) and Internet routes (filled with IPv4 BGP)

– VRF tables for sets of sites with identical routing requirements

– VRFs filled with information from CE routers and MP-BGP

information from other PE routers

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VPN Packet Forwarding Across

an MPLS VPN Backbone

Question: How will the PE routers forward the VPN packets across the

MPLS VPN backbone?

Answer #1: They will label the VPN packets with an LDP label for the egress

PE router and forward the labeled packets across the MPLS backbone.

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VPN Packet Forwarding Across

an MPLS VPN Backbone

Question: How will the PE routers forward the VPN packets across the

MPLS VPN backbone?

However, the egress PE router does not know which VRF to use for packet

switching, so the packet is dropped.

How about using a label stack?

Answer #1: They will label the VPN packets with an LDP label for the egress

PE router and forward the labeled packets across the MPLS backbone.

Results:

The P routers perform the label switching, and the packet reaches the

egress PE router.

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VPN Packet Forwarding Across

an MPLS VPN Backbone

Question: How will the PE routers forward the VPN packets across the

MPLS VPN backbone?

Answer #2: They will label the VPN packets with a label stack, using the LDP label for

the egress PE router as the top label, and the VPN label assigned by the

egress PE router as the second label in the stack.

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VPN Packet Forwarding Across

an MPLS VPN Backbone

Question: How will the PE routers forward the VPN packets across the

MPLS VPN backbone?

Result:The P routers perform label switching, and the packet reaches the egress

PE router.

The egress PE router performs a lookup on the VPN label and forwards the packet

toward the CE router.

Answer #2: They will label the VPN packets with a label stack, using the LDP label for

the egress PE router as the top label, and the VPN label assigned by the

egress PE router as the second label in the stack.

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VPN Penultimate Hop Popping

Penultimate hop popping can be performed on the last P router.

The egress PE router performs label lookup only on the VPN label,

resulting in faster and simpler label lookup

IP lookup is performed only once—in the ingress PE router.

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Penultimate hop popping can be performed on the last P router.

The egress PE router performs label lookup only on the VPN

label, resulting in faster and simpler label lookup

IP lookup is performed only once—in the ingress PE

router.

VPN Penultimate Hop Popping

router.

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VPN Label Propagation

Question: How will the ingress PE router get the second label in the

label stack from the egress PE router?

Answer: Labels are propagated in MP-BGP VPNv4 routing updates.

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VPN Label Propagation (Cont.)

Step 1: A VPN label is assigned to every VPN route by the egress

PE router.

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VPN Label Propagation (Cont.)

Step 1: A VPN label is assigned to every VPN route by the egress

PE router.

Step 2: The VPN label is advertised to all other PE routers in an MP-BGP

update.

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VPN Label Propagation (Cont.)

Step 1: A VPN label is assigned to every VPN route by the egress

PE router.

Step 2: The VPN label is advertised to all other PE routers in an MP-BGP

update.

Step 3: A label stack is built in the VRF table.

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For internal circulation of BSNL only