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

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
5 High 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 at
boundaries
14
PCEP, Netconf, BGP
BRKRST-2124
SR
PCE
Low-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
16001
16002
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

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

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
1.1.1.2/32
Prefix-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
Packet
Packet

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 IPv6
IPv4
VPN
IPv6
VPN
VPWS VPLS
Packet
Transport LDP
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

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 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-Latency
Use-Case
• Head-end computes a SID-list that expresses the shortest-path according to the
selected metric
segment-routing
traffic-eng
policy POLICY1
color 20 end-point ipv4 1.1.1.3
candidate-paths
preference 100
dynamic mpls
metric
type te
Node1
T:15
I:10
T:15
I:10
T:10
I:30
T:8
I:10
BRKRST-2124 41

segment-routing
traffic-eng
policy POLICY1
candidate-paths
preference 100
dynamic mpls
metric
type igp
association group 1 type node
!
policy POLICY2
candidate-paths
preference 100
dynamic mpls
metric
type igp
association group 1 type node
2 3
5 6
4 71
I:100
Default IGP link metric: I:10
I:100
POLICY1 SID-list:
<16002, 30203, 16007>
POLICY2 SID-list:
<16005, 16006, 16007>
Service Disjointness from the same head-end
Use-Case
• The head-end computes two,
disjoint paths
Node1
BRKRST-2124 42

Different VPNs need different underlay SLA
Single Domain Topology
2
6
1 CE
5
4
I: 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
4
I: 50
T: 15
On-Demand SR Policy work-flow
➊ BGP: 20/8 via
CE
20/8
RR
➋ BGP: 20/8 via PE4
VPN-LABEL: 99999
Low-latency (color 20)
➌ BGP: 20/8 via PE4
VPN-LABEL: 99999
router bgp 1
neighbor 1.1.1.10
address-family vpnv4 unicast
!
segment-routing
traffic-eng
on-demand color 20
preference 100
metric
type te
➍ PE4 with Low-
latency (color 20)?
➎ use template
color 20
➏  SID-list
<16002, 30204>
➎
SR Policy template
BRKRST-2124 45

2
6
1 CE
5
4
I: 50
T: 15
Automated performant steering
➊ BGP: 20/8 via
CE
20/8
RR
➋ 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
• 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

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• Related sessions
62BRKRST-2124

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
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
• Step3: LDP is removed from the nodes in
the network
• 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 PCE
PCE-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
Application
Path
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
!
!
!
76
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
!
!
!
78
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
!
!
!
79
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 Feature
NXOS
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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Cisco Live! :: Introduction to Segment Routing :: BRKRST-2124 | Las Vegas 2017