Cisco Live! :: Introduction to Segment Routing :: BRKRST-2124 | Las Vegas 2017

Introduction to Segment Routing

Michael Kowal, Vertical Solutions Architect@ciscomk

BRKRST-2124

© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public

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© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public 4BRKRST-2124

Abstract

This session provides an overview of the segment routing technology and its use cases. This new routing paradigm provides high operational simplicity and maximum network scalability and flexibility. You will get an understanding of the basic concepts behind the technology and its wide applicability ranging from simple transport for MPLS services, disjoint routing, traffic engineering and its benefits in the context of software defined networking.

Previous knowledge of IP routing and MPLS is required.

Introduction to Segment Routing

• Technology Overview

• Use Cases

• A Closer Look at the Control and Data Planes

• Traffic Protection

• Traffic Engineering

• Conclusion

Agenda

Technology Overview


Segment Routing

• Source Routing

• the source chooses a path and encodes it in the packet header as an ordered list of segments

• the rest of the network executes the encoded instructions

• Segment: an identifier for any type of instruction

• forwarding or service

• This presentation: IGP-based forwarding construct

7BRKRST-2124


Segment Routing – Forwarding Plane

• MPLS: an ordered list of segments is represented as a stack of labels

• IPv6: an ordered list of segments is encoded in a routing extension header

• This presentation: MPLS data plane

• Segment → Label

• Basic building blocks distributed by the IGP or BGP

8BRKRST-2124


IGP Prefix Segment

• Shortest-path to the IGP prefix

• Equal Cost Multipath (ECMP)-aware

• Global Segment

• Label = 16000 + Index

• Index of NodeX = X is used for illustrative purposes

• Distributed by ISIS/OSPF

9BRKRST-2124

DC (BGP-SR)

10

11

12

13

14

2 4

6 5

7

WAN (IGP-SR)

3

1

PEER

16005


IGP Adjacency Segment

• “Pop and Forward on the IGP adjacency”

• Local Segment

• Dynamically allocated

• Value “30X0Y” used for illustration

• X is the “from”

• Y is the “to”

• Advertised as a label value

• Distributed by ISIS/OSPF

10BRKRST-2124

DC (BGP-SR)

10

11

12

13

14

2 4

6 5

7

WAN (IGP-SR)

3

1

PEER

30204


BGP Prefix Segment

• Shortest-path to the BGP prefix

• Global Segment

• 16000 + Index

• Index of NodeX = X is used for illustrative purposes

• Signaled by BGP

11

DC (BGP-SR)

10

11

12

13

14

2 4

6 5

7

WAN (IGP-SR)

3

1

PEER

16001

BRKRST-2124


BGP Peering Segment

• “Pop and Forward to the BGP peer”

• Local Segment

• Dynamically allocated

• Value 40X0Y (for illustration)• X is the “from”

• Y is the “to”

• Signaled by BGP-LS (topology information) to the controller

12

DC (BGP-SR)

10

11

12

13

14

2

6

7

WAN (IGP-SR)

3

1

PEER

Low Lat,

Low BW

4

5High Lat, High BW

40407

BRKRST-2124


Multi-Domain Topology

• SR Path Computation Element (PCE)

• PCE collects via BGP-LS• IGP segments

• BGP segments

• Topology

13

DC (BGP-SR)

10

11

12

13

14

2 4

6 5

7

WAN (IGP-SR)

3

1

PEER

Low Lat, Low BW

BGP-LS

BGP-LS

BGP-LS

BRKRST-2124

SR

PCE


End-to-End Policy, Unified Data Plane• Construct a path by

combining segments to form an end-to-end path:• 16001 (Prefix-SID)

• 16002 (Prefix-SID)

• 30204 (Adj-SID)

• 40407 (Peer-SID)

• Per-application flow engineering

• Millions of flows• No signaling

• No midpoint state

• No reclassification atboundaries

14

PCEP, Netconf, BGP

BRKRST-2124

SR

PCELow-Latency to 7

for application …

DC (BGP-SR)

10

11

12

13

14

2 4

6 5

7

WAN (IGP-SR)

3

1

PEER

Low Lat

Low BW

50

Default ISIS cost metric: 10

16001

1600116002

30204

40407

{16001,

16002,

30204,

40407 }


Segment Routing Standardization• IETF standardization in SPRING working

group

• Protocol extensions progressing in multiple groups• IS-IS• OSPF• PCE• IDR• 6MAN• BESS

• Broad vendor support

• Strong customer adoption• WEB, SP, Enterprise

15

Sample IETF Documents

Problem Statement and Requirements

(RFC 7855)

Segment Routing Architecture

(draft-ietf-spring-segment-routing)

IPv6 SPRING Use Cases

(draft-ietf-spring-ipv6-use-cases)

Segment Routing with MPLS data plane

(draft-ietf-spring-segment-routing-mpls)

Topology Independent Fast Reroute using Segment Routing

(draft-bashandy-rtgwg-segment-routing-ti-lfa)

IS-IS Extensions for Segment Routing

(draft-ietf-isis-segment-routing-extensions)

OSPF Extensions for Segment Routing

(draft-ietf-ospf-segment-routing-extensions)

PCEP Extensions for Segment Routing

(draft-ietf-pce-segment-routing)

Close to 40 IETF drafts in progress

BRKRST-2124

https://tools.ietf.org/html/rfc7855

http://tools.ietf.org/html/draft-ietf-spring-segment-routing

http://tools.ietf.org/html/draft-ietf-spring-ipv6-use-cases

https://tools.ietf.org/html/draft-ietf-spring-segment-routing-mpls-04

https://tools.ietf.org/html/draft-bashandy-rtgwg-segment-routing-ti-lfa-00

http://tools.ietf.org/html/draft-ietf-isis-segment-routing-extensions

http://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extensions

http://datatracker.ietf.org/doc/draft-ietf-pce-segment-routing/


Segment Routing Product Support

• Platforms:

• IOS-XR (ASR9000, CRS-1/CRS-3, NCS5000, NCS5500, NCS6000)

• IOS-XE (ASR1000, CSR1000v, ASR902, ASR903, ASR920, ISR4400)

• NX-OS (N3K, N9K)

• Open Source (FD.io/VPP, Linux Kernel, ODL, ONOS, OpenWRT)

• PCE (WAN Automation Engine, XTC)

16BRKRST-2124

Use Cases


Simple and Efficient Transport of MPLS services

• No change to service configuration

• MPLS services ride on the prefix segments

• Simple: IGP-only

• One less protocol to operate

• No LDP, no RSVP-TE

SR Domain vrf REDvrf RED

7 1

3 4

2 8

5 6

MP-BGP

1.1.1.2/32Prefix-SID 16002 10.0.0.0/30

2001::a00:0/126

CE CEPE PE

Packet to 8

vpn

16002

Packet to 8

vpn

Packet to 8

Packet to 8

vpn

16002

BRKRST-2124 18


Interworking with LDP

• SR to LDP Interworking requires Mapping Server functionality • E.g. Nodes 6 & 8 can

advertise prefix-SIDs in IGP, on behalf of non-SR nodes.

• SR nodes install these prefix-SIDs in their forwarding table.

• Mapping server is a control plane mechanism and doesn’t have to be in the data path

• LDP to SR Interworking is Automatic and Seamless.

19

1

2 3

4

6 5

7

Site 1 Site 2

BRKRST-2124

Mapping-servers

1.1.1.4/32 SID 16004

1.1.1.7/32 SID 16007

8

Packet

vpn

16007

Packet

vpn

16007

Packet

vpn

LDP(7)

Packet

vpn

PacketPacket


Topology-Independent LFA (TI-LFA FRR)

• 50msec FRR in any topology• Link, Node, or SRLG

• IGP Automated

• No LDP, no RSVP-TE

• Optimum

• Post-convergence path

• No midpoint backup state

• Detailed operator report• S. Litkowski, B. Decraene, Orange

• WAN Automation Engine Design• How many backup segments?

• Perform capacity analysis

20

1

2 3

4

6 5

7

BRKRST-2124

Packet

16007

Packet

16007

Packet

16007

16005


Automated Traffic Matrix Collection

• Traffic Matrix is fundamental for• capacity planning

• centralized traffic engineering

• IP/Optical optimization

• Most operators do not have an accurate traffic matrix

• With SR, the traffic matrix collection is automated

21BRKRST-2124

1 2 3 4

1

2

3

4

1

2

4

3


Optimized Content Delivery

• On a per-content, per-user basis, the content delivery application can engineer • the path within the AS

• the selected border router

• the selected peer

• Also applicable for engineering egress traffic from DC to peer• BGP Prefix and Peering Segments

22

1 2

6

4 3

AS1

5

7

AS6AS5

AS7

BRKRST-2124

Packet

16002

16003

40206

A Closer Look at the Control and Data Planes

© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public 24

MPLS Control and Forwarding Operation with Segment Routing

PE1 PE2

IGPPE1 PE2

Services

IPv4 IPv6IPv4

VPN

IPv6

VPNVPWS VPLS

Packet

TransportLDP

MPLS Forwarding

RSVP BGPStatic IS-IS OSPF

No changes to

control or

forwarding plane

IGP or BGP label

distribution for

IPv4 and IPv6.

Forwarding plane

remains the same

MP-BGP

BRKRST-2124


• Prefix SID • Uses SR Global Block (SRGB)

• SRGB advertised with router capabilities TLV

• In the configuration, Prefix-SID can be configured as an absolute value or an index

• In the protocol advertisement, Prefix-SID is always encoded as a globally unique index

Index represents an offset from SRGB base, zero-based numbering, i.e. 0 is 1st index

E.g. index 1 SID is 16,000 + 1 = 16,001

• Adjacency SID • Locally significant

• Automatically allocated for each adjacency

• Always encoded as an absolute (i.e. not indexed) value

SID Encoding

SRGB = [ 16,000 – 23,999 ] – Advertised as base = 16,000, range = 8,000

Prefix SID = 16,001 – Advertised as Prefix SID Index = 1

Adjacency SID = 24000 – Advertised as Adjacency SID = 24000

SR enabled node

BRKRST-2124 25


SR IS-IS Control Plane Overview

• IS-IS Segment Routing functionality• IPv4 and IPv6 control plane

• Level 1, level 2 and multi-level routing

• Prefix Segment ID (Prefix-SID) for host prefixes on loopback interfaces

• Adjacency Segment IDs (Adj-SIDs) for adjacencies

• Prefix-to-SID mapping advertisements (mapping server)

• MPLS penultimate hop popping (PHP) and explicit-null signaling

BRKRST-2124 26


router isis 1

address-family ipv4 unicast

metric-style wide

segment-routing mpls

!


metric-style wide


!

interface Loopback0

passive


prefix-sid absolute 16001

!



!

!

IS-IS Configuration – Example

Ipv4 Prefix-SID value for

loopback0

Wide metrics

enable SR IPv4 control plane and

SR MPLS data plane on all ipv4

interfaces in this IS-IS instance

Wide metrics

enable SR IPv6 control plane and

SR MPLS data plane on all ipv6

interfaces in this IS-IS instance

Ipv6 Prefix-SID value for

loopback0

SID index 1

1.1.1.11.1.1.2

1.1.1.4 1.1.1.6

DIS

BRKRST-2124 27


SR OSPF Control Plane Overview

• OSPF Segment Routing functionality• OSPFv2 control plane

• Multi-area

• IPv4 Prefix Segment ID (Prefix-SID) for host prefixes on loopback interfaces

• Adjacency Segment ID (Adj-SIDs) for adjacencies

• Prefix-to-SID mapping advertisements (mapping server)

• MPLS penultimate hop popping (PHP) and explicit-null signaling

BRKRST-2124 28


router ospf 1

router-id 1.1.1.1


area 0

interface Loopback0

passive enable


!

!

!

OSPF Configuration Example

Prefix-SID for loopback0

Enable SR on all areas

SID index 1

1.1.1.11.1.1.2

1.1.1.5 1.1.1.3

DR

1.1.1.4

BRKRST-2124 29


MPLS Data Plane Operation

• Packet forwarded along IGP shortest path (ECMP)

• Swap operation performed on input label

• Same top label if same/similar SRGB

• PHP if signaled by egress LSR

Payload

SRGB [16,000 – 23,999 ]

X

Payload

Swap

X

Payload

SRGB [16,000 – 23,999 ]

Y

Payload

Pop

Y

Adjacency

SID = X

X

Prefix SID Adjacency SID

Packet forwarded along IGP adjacency

Pop operation performed on input label

Top labels will likely differ

Penultimate hop always pops last adjacency SID

BRKRST-2124


Payload

VPN Label

31

MPLS Data Plane Operation (Prefix SID)

SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ]

Loopback X.X.X.X

Prefix SID Index = 41

A B C D

Payload

16041

Payload

Push

Push

Swap Pop

Payload Payload

VPN Label

16041

VPN Label

Pop

BRKRST-2124


Payload

VPN Label

32

MPLS Data Plane Operation (Adjacency SIDs)

Payload

16041

Payload

Push

Push

Push

Pop Pop

Payload Payload

VPN Label

16041

VPN Label

Pop

Adjacency

SID = 30206

30206

A B X D

BRKRST-2124

Loopback X.X.X.X

Prefix SID Index = 41

SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ] SRGB [16,000 – 23,999 ]


MPLS LFIB with Segment Routing

• LFIB populated by IGP (ISIS / OSPF)

• Other protocols (LDP, RSVP, BGP) can still program LFIB

• Forwarding table remains constant (Nodes + Adjacencies) regardless of number of paths

33

PE

PE

PE

PE

PE

PE

PE

PE

P

In

Label

Out

Label

Out

Interface

L1 L1 Intf1

L2 L2 Intf1

… … …

L8 L8 Intf4

L9 L9 Intf2

L10 Pop Intf2

… … …

Ln Pop Intf5

Network

Node

Segment Ids

Node

Adjacency

Segment Ids

Forwarding

table remains

constant

BRKRST-2124

Traffic Protection


Topology Independent LFA (TI-LFA) – Benefits

• 100%-coverage 50-msec link, node, and SRLG protection

• Simple to operate and understand• automatically computed by the IGP

• Prevents transient congestion and suboptimal routing• leverages the post-convergence path, planned to carry the traffic

• Incremental deployment• also protects LDP and unlabeled traffic

35BRKRST-2124


TI-LFA – Zero-Segment Example

• TI-LFA for link R1R2 on R1

• Calculate post-convergence SPT• SPT with link R1R2 removed from

topology

• Derive SID-list to steer traffic on post-convergence path empty SID-list

• R1 will steer the traffic towards LFA R5

36BRKRST-2124

1000

Default metric: 10

A

55

4

Packet to Z

Packet to Z

prefix-SID(Z)

1 2

Z

3

Packet to Z

prefix-SID(Z)


TI-LFA – Single-Segment Example


• Calculate post-convergence SPT

• Derive SID-list to steer traffic on post-convergence path <Prefix-SID(R4)>• Also known as “PQ-node”

• R1 will push the prefix-SID of R4 on the backup path

37BRKRST-2124

Packet to Z

prefix-SID(Z)

prefix-SID(R4)

Default metric:10

5

21

A Z

3

Packet to Z

prefix-SID(Z)

Packet to Z

4

Packet to Z

prefix-SID(Z)

4


TI-LFA – Double-Segment Example


• Calculate post-convergence SPT

• Derive SID-list to steer traffic on post-convergence path <Prefix-SID(R4), Adj-SID(R4-R3)• Also known as “P- and Q-node”

• R1 will push the prefix-SID of R4 and the adj-SID of R4-R3 link on the backup path

Default metric: 10

5

21

A Z

R3R4 34

Packet to Z

prefix-SID(Z)

Packet to Z

Packet to Z

prefix-SID(Z)

adj-SID(R4-R3)

prefix-SID(R4)

Packet to Z

prefix-SID(Z)

adj-SID(R4-R3)

1000

Packet to Z

prefix-SID(Z)

Traffic Engineering

(SR-TE)


Traffic Engineering with Segment Routing

• Provides explicit routing

• Supports constraint-based routing

• Supports centralized admission control

• Uses existing ISIS / OSPF extensions to advertise link attributes

• No RSVP-TE to establish LSPs

• Supports ECMP

40

TE LSP

Segment

Routing

BRKRST-2124


2 3

4

1

Default IGP link metric: I:10

Default TE link metric: T:10

5

SID-list: <16005, 16004, 16003>

6

Low-LatencyUse-Case

• Head-end computes a SID-list that expresses the shortest-path according to the selected metric

segment-routingtraffic-eng

policy POLICY1color 20 end-point ipv4 1.1.1.3candidate-paths

preference 100dynamic mpls

metrictype te

No

de

1

T:15

I:10

T:15

I:10

T:10

I:30

T:8

I:10

BRKRST-2124 41


segment-routingtraffic-engpolicy POLICY1color 20 end-point ipv4 1.1.1.7candidate-pathspreference 100dynamic mplsmetrictype igpassociation group 1 type node

!policy POLICY2color 30 end-point ipv4 1.1.1.7candidate-pathspreference 100dynamic mplsmetrictype igpassociation group 1 type node

2 3

5 6

4 71

I:100

Default IGP link metric: I:10

I:100POLICY1 SID-list:

<16002, 30203, 16007>

POLICY2 SID-list:

<16005, 16006, 16007>

Service Disjointness from the same head-endUse-Case

• The head-end computes two, disjoint paths

No

de

1

BRKRST-2124 42


Different VPNs need different underlay SLASingle Domain Topology

2

6

1 CE

5

4I: 50

Default IGP cost: I:10

Default TE cost: T:10

IGP cost 30

T: 15

2

6

1 CE

5

4

TE cost 20

Basic VPN should

use lowest cost

underlay path

Premium VPN

should use lowest

latency path

Objective:

operationalize this

service for simplicity,

scale and

performanceI: 50

T: 15



BRKRST-2124 44


2

6

1 CE

5

4I: 50

T: 15

On-Demand SR Policy work-flow

➊ BGP: 20/8 via

CE

20/8

RR➋ BGP: 20/8 via PE4

VPN-LABEL: 99999

Low-latency (color 20)

➌ BGP: 20/8 via PE4

VPN-LABEL: 99999


router bgp 1neighbor 1.1.1.10address-family vpnv4 unicast

!segment-routingtraffic-engon-demand color 20preference 100 metrictype te

➍ PE4 with Low-

latency (color 20)?

➎ use template

color 20

➏ SID-list

<16002, 30204>

➎



SR Policy template Low-latency (color 20)

BRKRST-2124 45


2

6

1 CE

5

4I: 50

T: 15

Automated performant steering

➊ BGP: 20/8 via

CE

20/8

RR➋ BGP: 20/8 via PE4

VPN-LABEL: 99999


➌ BGP: 20/8 via PE4

VPN-LABEL: 99999


➍ PE4 with Low-

latency (color 20)?

➎ use template

color 20

➏ SID-list

<16002, 30204>

FIB table at PE1

SRTE: 4001: Push <16002, 30204>

➐ instantiate

SR Policy

BSID 4001

Low Latency to PE4

➐

➑ forward 20/8

via BSID 4001

➑➐

BGP: 20/8 via 4001



In Out Out_intf Fraction

4001 <16002, 30204> To Node 2 100%

Forwarding table on Node1

BRKRST-2124 47


SR-TE• Simple, Automated and Scalable

• No core state: state in the packet header

• No tunnel interface: “SR Policy”

• No head-end a-priori configuration: on-demand policy instantiation

• No head-end a-priori steering: automated steering

• Multi-Domain

• XR Traffic Controller (XTC) for compute

• Binding-SID (BSID) for scale

• Lots of Functionality

• Designed with lead operators along their use-cases

BRKRST-2124 55

Conclusion


Conclusion

• Simple routing extensions to implement source routing

• Packet path determined by prepended segment identifiers (one or more)

• Data plane agnostic (MPLS, IPv6)

• Increase network scalability and agility by reducing network state and simplifying control plane

• Traffic protection with 100% coverage with more optimal routing

Recommended Follow-up Session:Segment Routing: Technology deep-dive and advanced use cases (BRKRST-3122)

57BRKRST-2124


Segment Routing Sessions

Breakout Sessions Labs

Introduction to Segment Routing (BRKRST-2124) ←you are here SP SDN - Segment Routing in Action (LTRMPL-2201)

Segment Routing: Technology Deep-Dive and Advanced

Use Cases (BRKRST-3122)

MPLS Segment Routing Introduction (LABSPG-1020)

Troubleshooting Segment Routing (BRKRST-3009) Segment Routing for Policy Aware Network (LABRST-1015)

Application Engineered Routing: Allowing Applications to

Program the Network (BRKSPG-2066)

Next Generation Service Provider Network using Segment

Routing & BIER (LABSPG-2012)

Automated Networks with Segment Routing in the

Datacenter (BRKDCN-2050)

Segment Routing in Datacenter using Nexus 9000/3000

(LABDCN-2020)

Multicast and Segment Routing (BRKIPM-2249) DevNet Workshop – Application Engineered Egress Routing

(DEVNET-2062)

Evolving Network Application Use-Cases Using Segment

Routing In the Enterprise (BRKMPL-2118)

DevNet Workshop-WAN Automation Engine API

(DEVNET-2035)

Cisco Live 2017


Stay Up-To-Date

http://www.segment-routing.net/

https://www.linkedin.com/groups/8266623

https://twitter.com/SegmentRouting

https://www.facebook.com/SegmentRouting/ amzn.com/B01I58LSUO

BRKRST-2124 59

http://www.segment-routing.net/

https://www.linkedin.com/groups/8266623

https://twitter.com/SegmentRouting

https://www.facebook.com/SegmentRouting/

https://amzn.com/B01I58LSUO


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62BRKRST-2124

Thank you

Backup Slides


Migration Scenario: LDP to SR

• Initial state: All nodes run LDP, not SR

66BRKRST-2124

1 LDP

3 4

2

5 6

LDP Domain

LDP LDP

LDP LDP

LDP LDP




• Step1: All nodes are upgraded to SR• In no particular order

• Default label imposition preference = LDP

67BRKRST-2124

1 LDP

3 4

2

5 6

SR+LDP Domain

SR+LDP SR+LDP

SR+LDP SR+LDP

SR+LDP SR+LDP





• leave default LDP label imposition preference

• Step2: All PEs are configured to prefer SR label imposition• In no particular order

68BRKRST-2124

SR+LDP Domain

1 SR

3 4

2

5 6

SR+LDP SR+LDP

SR+LDP SR+LDP

SR+LDP

segment-routing mpls sr-prefer





• leave default LDP label imposition preference

• Step2: All PEs are configured to prefer SR label imposition• In no particular order

• Step3: LDP is removed from the nodes in the network• In no particular order

• Final state: All nodes run SR, not LDP

69BRKRST-2124

SR Domain

1 SR

3 4

2

5 6

SR SR

SR SR

SR SR


How Traffic Engineering Works

• Link information Distribution• ISIS-TE

• OSPF-TE

• Path Calculation

• Path Setup

• Forwarding Traffic down path• Auto-route (announce / destinations)

• Static route

• PBR

• PBTS / CBTS

• Forwarding Adjacency

• Pseudowire Tunnel select

70

IP/MPLS

Head end

Mid-point Tail end

TE LSP

BRKRST-2124


Stateful PCE

• PCE maintains topology and path database (established paths)

• More optimal centralized path computation

• Enables centralized path initiation and update control

• Well suited for SDN deployments

71

PCEP

Stateful PCE

TED

LSP DB

PCC

BRKRST-2124


Topology Acquisition

• An external PCE requires some form of topology acquisition

• A PCE may learn topology using BGP-LS, IGP, SNMP, etc.

• BGP-LS characteristics• aggregates topology across one or more domains

• provides familiar operational model

• New BGP-LS attribute TLVs for SR • IGP: links, nodes, prefixes

• BGP: peer node, peer adjacency, peer set

72

Domain 1 Domain 2

Domain 0

BGP-LS

TED

BGP-LS BGP-LS

RR

PCE

BRKRST-2124


Active Stateful PCE

• PCC or PCE may initiate path setup

• PCC may delegate update control to PCE

• PCC may revoke delegation

• PCE may return delegation

73

PCEP

Active Stateful PCE

TED

LSP DB

Stateful

PCC

PCE has update

control over

delegated paths

BRKRST-2124


Active Stateful PCEPCE-Initiated and PCC-Initiated LSPs

• PCE part of controller architecture managing full path life cycle

• Tighter integration with application demands

PCEP

PCC-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful

PCC

PCEP

PCE-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful

PCC

PCC initiates

LSP and

delegates

update

control

PCE initiates

LSP and

maintains

update control

PCC may initiate path setup based on distributed network state

Can be used in conjunction with PCE-initiated paths

BRKRST-2124


PCE Extensions for Segment Routing (SR)• Segment routing enables source routing

based on segment ids distributed by IGP

• PCE specifies path as list of segment ids

• PCC forwards traffic by pushing segment id list on packets

• No path signaling required

• Minimal forwarding state

• Maximum network forwarding virtualization

• The state is no longer in the network but in the packet

• Paths may be PCE- or PCC-initiated

75

PCEP

Segment List:: 10,20,30,40

Stateful PCE

TED

LSP DB

Stateful

PCC

Node

SID

Adjacency

SID

Forwarding

table remains

constant

In Out Int

L1 L1 Intf1

… … …

L7 L7 Int3

L8 Pop Intf3

… … …

L9 Pop Intf5

ApplicationPath

Request

BRKRST-2124


router isis DEFAULT

net 49.0001.1720.1625.5001.00


metric-style wide


!

interface Loopback0

passive



!

!

interface GigabitEthernet0/0/0/0


fast-reroute per-prefix

fast-reroute per-prefix ti-lfa

!

!

!

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Configuring Topology Independent Fast Reroute for IPv4 using Segment Routing and IS-IS (Cisco IOS XR)

Enable TI-LFA for IPv4 prefixes on


BRKRST-2124


router isis DEFAULT

net 49.0001.1720.1625.5001.00


metric-style wide


!

interface Loopback0

passive



!

!



fast-reroute per-prefix

fast-reroute per-prefix ti-lfa

!

!

!

77

Configuring Topology Independent Fast Reroute for IPv6 using Segment Routing and IS-IS (Cisco IOS XR)

Enable TI-LFA for IPv6 prefixes on


BRKRST-2124


router isis DEFAULT

net 49.0001.1720.1625.5001.00


metric-style wide


segment-routing prefix-sid-map receive

segment-routing prefix-sid-map advertise-local

!

...

!

segment-routing

address-family ipv4

prefix-sid-map

172.16.255.1/32 4041 range 8

!

!

!

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Configuring a Mapping Server for SR and LDP Interworking for IPv4 Using IS-IS (Cisco IOS XR)

Local prefix-to-SID mapping policy

172.16.255.1/32 – 4041

:

172.16.255.8/32 - 4048

Construct active mapping policy using

remotely learned and locally configured

mappings (mapping client)

Advertise local mapping policy (mapping

server)

BRKRST-2124


router isis DEFAULT

net 49.0001.1720.1625.5001.00


metric-style wide


segment-routing prefix-sid-map receive

!

interface Loopback0

passive



!

!


point-to-point


!

!

!

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Configuring a Mapping Client for SR and LDP Interworking for IPv4 Using IS-IS (Cisco IOS XR)

Construct active mapping policy using

remotely learned and locally configured

mappings (mapping client)

BRKRST-2124


Enabling Segment Routing FeatureNXOS

feature bgp

install feature-set mpls

feature-set mpls

feature mpls l3vpn

feature mpls segment-routing

Under Interface configuration:

mpls ip forwarding

Commands:

BRKRST-2124 80

Cisco Live! :: Introduction to Segment Routing :: BRKRST-2124 | Las Vegas 2017

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Transcript of Cisco Live! :: Introduction to Segment Routing :: BRKRST-2124 | Las Vegas 2017