GBS MPLS Introduction

confidentialGBS-MKT-Global-10_001

Monaco, 2011-09-08

MPLS Introduction

Executive Training Session

Delivered to CW (M&I)

GBS-MKT-Global-10_001Global Business Solutions SAL

• Introduction

• Application

• Features

• Implementation

• Audit Service

Agenda


• Basic Concept

• Architecture

• Operation Modes

• LSR Architecture

• Forwarding

• Label & Stack

Introduction


• MPLS?

� Multi-Protocol Label Switching

� New forwarding mechanism based on labels• Destination IP networks (traditional routing)

• Source network, QoS, bandwidth, etc…

� Support other forwarding mechanism

Basic Concept


• Edge routers:� Lookup routes

� Assign labels

• Core routers:� Switch packets

� Swap labels

• All forwarding based

MPLS Example


10.1.1.110.1.1.1

Routing lookup and

label assignment10.0.0.0/8 �� L=5

Label swappingL=5 �� L=3

Label removal and

routing lookupL=3

MPLS Example (image)


• MPLS architecture is divided between 2 main components:

• Control plane:� Exchange L3 routing info and labels

• Routing: OSPF, EIGRP, BGP, IS-IS, etc…

• Labels: TDP, LDP, BGP, RSVP, etc…

� Maintain the label switching database• LFIB: label forwarding information base

• Data plane:� Simple forwarding engine

MPLS Architecture


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

4��17

Labeled packet

Label 4

Labeled packet

Label 17

MPLS Architecture (image)


• MPLS can be used everywhere regardless of L1/2 (media/protocol)

• MPLS have 2 modes of operations:� Frame mode: insert a 32b label field between L2 and L3

� Cell mode: use other layer header (MPLS over ATM)

• MPLS domain is the group of core and edge routers (LSR) that work together.

MPLS Operation Modes


MPLS DomainMPLS DomainMPLS DomainMPLS Domain

Edge Edge Edge Edge

LSRLSRLSRLSR

LSRLSRLSRLSR

10.1.1.110.1.1.110.1.1.110.1.1.1 L=L=L=L=3333 L=L=L=L=5555

L=L=L=L=43434343L=L=L=L=3131313120.1.1.120.1.1.120.1.1.120.1.1.1

10.1.1.110.1.1.110.1.1.110.1.1.1

20.1.1.120.1.1.120.1.1.120.1.1.1

MPLS Domain (image)


• LSR (Label Switch Router) types:� Core LSR: forward labeled packet (swap labels)

� Edge LSR: labels packets and send them to domain

• LSR functions:� Exchange routing info

� Exchange labels

� Forward packets or cell (data plane)

LSR Architecture


LSR

Control plane

Data plane

Routing protocol

Label distribution protocol

Label forwarding table

IP routing table

Exchange ofrouting information

Exchange oflabels

Incoming

labeled packets

Outgoing

labeled packets

LSR Architecture (image)


• FEC (Forwarding Equivalent Class):

� IP Packet classification

� Group having same forwarding manner• Over the same path

• Having the same treatment

FEC


• MPLS forwarding:� Assign a packet to a FEC (label)

� Determine the next-hop (routing)

• LSR perform the following functions:� Insert (impose) a label or a stack of labels on ingress.

� Swap a label with a next-hop label or a stack of labels in the core.

� Remove (pop) a label on egress.

MPLS Forwarding


MPLS Forwarding (image)

MPLS Domain

10.1.1.1

IP Lookup

10.0.0.0/8 ��

label 3

LFIB

10.1.1.1/8 ��label 3

IP Lookup

10.0.0.0/8 ��

label 5

LFIBlabel 3 ��label 5

IP Lookup

10.0.0.0/8 ��

next hop

LFIBlabel 5 �� pop

10.1.1.13 10.1.1.15 10.1.1.1


• Label – 32b field between L2 & L3:� 20b: label (number)

� 3b: experimental (carry precedence value)

� 1b: bottom-of-stack (indicator if last label)

� 8b: TTL (prevent indefinite looping)

• Label Stack Scenarios:� MPLS/VPN (next router / VPN tunnel)

� Traffic Engineering (endpoint tunnel / destination)

� Combined MPLS/VPN & Traffic Engineering

Label & Stack


• Unicast IP routing

• Multicast IP routing

• Traffic Engineering

• QoS

• VPN

Applications differ only in the control plane

Applications


• IP routing protocol (OSPF, EIGRP, …)� Carry info about network reachability

• Label distribution protocol (LDP or TDP)� Bind labels to networks learned

• FEC = destination network� Stored in the routing table

Unicast IP routing


• No dedicated protocol is needed� Natively built into MPLS

� PIMv2 propagate routes and labels

• FEC = destination multicast address� Stored in the multicast table

Multicast IP routing


• IP routing protocol (OSPF or IS-IS)� Holds the entire routing topology

� IGP is an extension to MPLS/TE

• Establish tunnel (RSVP or CR-LDP)� Propagate labels

• IGP: internal gateway protocol

• RSVP: resource reservation protocol

• CR-LDP: constraint-based routed LDP

Traffic Engineering


• Extension to unicast� Differentiated services

� LDP/TDP extension

• FEC = destination network + service class

QoS


• Networks are learned via:� IGP from a customer

� BGP from internal routers

• Label propagate via multi-protocol BGP� 1st: points to the egress router (LDP or TDP)

� 2nd: points to a routing table or egress interface

• FEC=VPN site descriptor or routing table

VPN


Control plane

MulticastIP Routing

MPLS Traffic Engineering

QoS MPLS/VPNUnicast IP Routing

Data plane

Any IGP

LDP/TDP

Label forwarding table

Unicast IProuting table

PIM version 2

MulticastIP routing table

OSPF or IS-IS

LDP


RSVP

Any IGP

LDP/TDP


Any IGP

LDP

Unicast IProuting tables

BGP

Applications (image)


• AToM: Any Transport over MPLS� L2 frames: Ethernet, FR, ATM, PPP, HDLC

� Transport L2 traffic over IP/MPLS backbone

� Single, integrated, packet based infrastructure

� Higher availability, performance, scalability

• Examples:� Ethernet over MPLS, application: TLS and VPLS

� Frame-Relay over MPLS, carry: BECN, FECN, BE

� ATM over MPLS

AToM


• Neighbors Discovery

• Label Distribution

• Packet Propagation

• Convergence

Features


• LDP & TDP have similar process:� Send “Hello” message on the interface (UDP)

� Respond by establishing a session (TCP)

� LDP port number is 646

� UDP multicast address 224.0.0.2

• LSR establish one LDP session per label space� Combination of frame mode, cell mode or multi cell

mode results in multiple LDP sessions

Neighbours Discovery


1.0.0.1 1.0.0.3

1.0.0.4

MPLS_D

1.0.0.2

UDP: Hello

(1.0.0.1:1050 � 224.0.0.2:646)

UDP: Hello

(1.0.0.1:1050 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1033 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1033 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1064 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1064 � 224.0.0.2:646)

UDP: Hello

(1.0.0.1:1051 � 224.0.0.2:646)

UDP: Hello

(1.0.0.1:1051 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1034 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1034 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1065 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1065 � 224.0.0.2:646)

UDP: Hello

(1.0.0.1:1052 � 224.0.0.2:646)

UDP: Hello

(1.0.0.1:1052 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1035 � 224.0.0.2:646)

UDP: Hello

(1.0.0.4:1035 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1066 � 224.0.0.2:646)

UDP: Hello

(1.0.0.2:1066 � 224.0.0.2:646)MPLS_B

MPLS_A NO_MPLS_C

Neighbours Discovery (image)


• Frame mode:� New field is used for forwarding decisions

� Labels are advertised to reachable peers

• Packet mode:� Build routing table

� Each LSR assign label to every destination

� All LSR announce their labels

� Each LSR build its data structures (LIB, LFIB, FIB)• LIB: label table,

• FIB: forwarding table,

• LFIB: current label table

Label Distribution


LSR

Control Plane

Data Plane

OSPF:

RT:

LIB:

FIB:

LFIB:

OSPF: OSPF: 10.0.0.0/810.0.0.0/8 � 1.2.3.4

10.0.0.0/8 � 1.2.3.4

10.0.0.0/8 � 1.2.3.410.1.1.1

LDP: 3LDP: 10.0.0.0/8, L=3

L=5 10.1.1.1

10.0.0.0/8 � Next-hop L=3, Local L=5LDP: 5LDP: 10.0.0.0/8, L=5

L=3 10.1.1.1

L=3 10.1.1.1L=5 � L=3

, L=3

Label Distribution (image)


• IP routing table:� Tables are build based on the routing protocol (L3)

� FIB are build based on routing table with no labeling

• Allocating labels:� Each LSR allocates a label asynchronously (local

significance)

� LIB and LFIB setup, action “pop”

• Advertisement:� Each LSR advertise all its neighbors (up/down stream)

� ALL LSR store received label on LIB

� Edge LSR store label from their next-hop in FIB

� Every LSR insert outgoing labels in LFIB

Packet Propagation (1)


• Packet propagation:� IP lookup is done in FIB, packet labeled (ingress LSR)

� Labeled packet lookup is performed in LFIB, label switched

� Label lookup is performed on LFIB, label removed (egress LSR) if action is “pop”

• Advantages:� Liberal label retention improves convergence speed

Packet Propagation (2)


Building the IP Routing Table

– IP routing protocols are used to build IP routing tables on all LSRs.

– FIBs are built based on IP routing tables with no labeling information.

Network Next-hop

X B

Routing table of A

Network Next-hop

X C

Routing table of B

Network Next-hop

X D

Routing table of C

Network Next-hop

X C

Routing table of ENetwork Next hop Label

X B —

FIB on A

A B C D

E

Network X

Packet Propagation (image)


A B C D

E

Network X

Router B assigns label 25 to

destination X.


Allocating Labels

– Every LSR allocates a label for every destination in the IP routing table.

– Labels have local significance.

– Label allocations are asynchronous.

Network Next-hop

X C

Routing table of B


A B C D

E

Network X

Router B assigns label 25 to

destination X.

Network LSR label

X local 25

LIB on BLocal label is stored in LIB.

Label Action Next hop

25 pop C

LFIB on B Outgoing action is pop, as B

has received no label for X

from C.


LIB and LFIB Setup

– LIB and LFIB structures have to be initialized on the LSR allocating the label.

Network Next-hop

X C

Routing table of B


A B C D

E

Network X

Network LSR label

X local 25

LIB on B

X = 25X = 25


Label Distribution

– The allocated label is advertised to all neighbor LSRs, regardless of whether the neighbors are upstream or downstream LSRs for the destination.


X = 25X = 25

Network LSR label

X B 25

LIB on ANetwork LSR label

X B 25

LIB on C

Network LSR label

X B 25

LIB on E

Network Next hop Label

X B 25

FIB on A

A B C D

E

Network X


Receiving Label Advertisement

– Every LSR stores the received label in its LIB

– Edge LSRs that receive the label from their next-hop also store the label information in the FIB


IP: X Lab: 25 IP: X


X B 25

FIB on A

IP lookup is performed in

FIB: packet is labeled.


25 pop C

LFIB on B

Label lookup is performed

in LFIB: label is removed.

A B C

E


Interim Packet Propagation

– Forwarded IP packets are labeled only on the path segments where the labels have already been assigned


Network LSR label

X B 25

local 47

LIB on C


47 pop D

LFIB on C

A B C D

E

Network XRouter C assigns label

47 to destination X.

X = 47


Further Label Allocation

– Every LSR will eventually assign a label for every destination


Network LSR label

X local 25

C 47

LIB on BNetwork Next hop Label

X C 47

FIB on B


25 47 C

LFIB on B

A B C D

E

X = 47

Network X


Populating LFIB

– Router B has already assigned a label to X and created an entry in the LFIB

– The outgoing label is inserted in the LFIB after the label is received from the next-hop LSR


IP: X IP: X

Ingress LSR Egress LSR

A B C

E

Lab: 25 Lab: 47


X B 25

FIB on A

IP lookup is performed in

the FIB, packet is labeled.


47 pop D

LFIB on C


in the LFIB, label is removed.


25 47 C

LFIB on B


in the LFIB, label is switched.



• Steady state: all LSR populated their LIB, LFIB and FIB

• Link failure:� entries are removed from data structure

� Rebuild the routing and forwarding tables

� LFIB & FIB rebuilt immediately from LIB

• Link recovery:� Routing protocols discovered

� IP routing tables rebuilt, as well FIB and LFIB

� Routing protocols optimize forwarding path

• Remarks:� End-to-end connectivity intermittently broken

� Traffic engineering (make-before-break) use

Convergence


Network Next-hop

X C

Routing table of BNetwork Next hop Label

X C 47

FIB on B

Network LSR label

X local 25

C 47

E 75

LIB on B


25 47 C

LFIB on B

A B C D

E

Network X

Convergence (image)

Steady State Description

– After the LSRs have exchanged the labels, LIB, LFIB and FIB data structures are completely populated.


Network Next-hop

X C

Routing table of B


X C 47

FIB on B

Network LSR label

X local 25

C 47

E 75

LIB on B


25 47 C

LFIB on B

�A B C D

E

Network X

�

Convergence (image)

Link Failure Actions

– Routing protocol neighbors and LDP neighbors are lost after a link failure.

– Entries are removed from various data structures.


Network LSR label

X local 25

C 47

E 75

LIB on B


25 47 C

LFIB on B


X E —

FIB on BNetwork Next-hop

X E

Routing table of B

A B C D

E

Network X

�

Convergence (image)

Routing Protocol Convergence

– Routing protocols rebuild the IP routing table and the IP forwarding table.


Network LSR label

X local 25

C 47

E 75

LIB on B

Network Next-hop

X E

Routing table of B


25 75 E

LFIB on B


X E 75

FIB on B

A B C D

E

Network X

�

Convergence (image)

MPLS Convergence

– The LFIB and labeling information in the FIB are rebuilt immediately after the routing protocol convergence, based on labels stored in the LIB.


Network LSR label

X local 25

C 47

E 75

LIB on B

Network Next-hop

X E

Routing table of B


25 75 E

LFIB on B


X E 75

FIB on B

A B C D

E

Network X

Convergence (image)

Link Recovery Actions

– Routing protocol neighbors are discovered after link recovery.


Network LSR label

X local 25

C 47

E 75

LIB on B


25 75 E

LFIB on B


X E 75

FIB on BNetwork Next-hop

X E

Routing table of B

C C —

pop C

A B C D

E

Network X

Convergence (image)

IP Routing Convergence After Link Recovery

– IP routing protocols rebuild the IP routing table.

– The FIB and the LFIB are also rebuilt, but the label information might be lacking.


• Guidelines

• Examples

Implementation


• Implementation guidelines depends on:

� Size of the network

� Geographical distribution

� Service classification

� Projected level of availability

� Convergence speed requirements

Guidelines


CE

CE

P/PE

CE

P/PE

Example I


CECE

PE

CE

P/PE P/PE

Example II


CE CE

PE

CE

P P

CE CE

PEPE

Example III


L2/L3 MPLS Routing & Switching Audit


L2/L3 MPLS Audit

• Pre-Requisites & Deliverables

• Activities Description

• Case Studies


Pre-Requisites & Deliverables

• Pre-Requisites� Network Diagram: logical diagrams representing the physical and

logical connectivity of all IP based nodes in the transport layer

� Systems Configuration: collection of both high and low level data representing the running setup of all the nodes in question

� Logging information: only if quickly available, a history of 1 month would be fine, otherwise we will highlight major node to collect output from upon reception of the network diagram

• Deliverables� High level service delivery diagram

� End to end service availability, performance, security and capacity

� Nodes status, highlighting major issues and impact on the service


• Assessment� Facts findings (LLD collection)

� Running Configuration building simulation

� Availability, performance, security and capacity

• Recommendation� Quick wins solutions (low cost that induce big results)

� Pitfalls avoidance (potential issues or problems)

� Phased plan (with cost & time estimate)

Activities Description


• Availability� End to end service identifications

� Highlighting potential failure scenarios

� Convergence latency issues

• Performance� Per LSR analysis (utilization, log, etc…)

� End to end service classification analysis

� Convergence speed matching service requirements

Case Studies


A

C

B

Example

The MPLS domain carriers both voice and data traffic

– In this example, end users on B are communicating with peers/destination through A.

– If the link between A and B fails, all traffic will be routed through C.

– Even with proper dimensioning, both links B-C & C-A will be congested and the LSR C will be overloaded, thus performance issue.

– In order to remediate this issue, simply converge voice traffic quickly, delay data convergence until platform is stable, (possibly limit further voice and/or data calls) and prioritize important traffic.

Internet

Voice-2

Voice-1

Data-1


Thank You

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GBS MPLS Introduction

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