Segment Routing Advanced Use Cases delivered at Cisco Live USA by Steve Braaten (BRKRST-3122)

2. Segment Routing: Technology
Update and Advanced Use-Cases
Steve Braaten, Solutions Architect
BRKRST-3122

3. • Segment Routing Executive Summary
• Reminders
• Incremental Deployment Use-Cases
• Inter-Domain Policy at Scale
• Topology Independent LFA (TI-LFA)
• Microloop Avoidance
• Conclusion
Agenda

4. Segment Routing
Executive Summary

5. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
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
• 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
• Multi-Vendor solution
BRKRST-3122 5

6. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Deployed !
• First deployments in 2015 – just 15 months after FCS !!!
• Strong start in 2016 with many new deployments
BRKRST-3122 6

7. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
IETF
• Strong commitment for standardization and
multi-vendor support
• SPRING Working-Group (started Nov 2013)
• All key documents are WG-status
• Over 25 drafts maintained by SR team
• Over 50% are WG status
• Over 75% have a Cisco implementation
• Several interop reports are available
• First RFC document - RFC 7855 (May 2016)
www.segment-routing.net
tools.ietf.org/wg/spring/
BRKRST-3122 7

8. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Foundation for modern IP/MPLS networking
• Simplicity
• Set of few, well-chosen building blocks
• Solution to unsolved problems
• End-to-end policy, local and/or centralized PCE, 50msec protection, microloop
avoidance, and more…
• Scale
• Granular traffic engineering with minimal network state
• Seamless Deployment
• SR/LDP interworking, SR/RSVP-TE interworking, ship-in-the-night co-existence
• Decoupled data and control planes
• Low-cost
1
BRKRST-3122 8

9. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Session Assumptions
• Thorough understanding of SR tutorial
• http://www.segment-routing.net/home/tutorial
• You should know
• SRGB
• IGP Prefix and Adj SID’s
• Anycast SID
• SR/LDP interworking
• BGP Prefix SID and the MSDC use-case
• Use-Cases in this presentation described for SR/MPLS
• Same concept applies to SRv6 (native IPv6 SR extension header, no MPLS)
BRKRST-3122 9

10. Reminders

11. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Prefix segment
• Shortest-path to the prefix
• Equal Cost MultiPath (ECMP)-aware
• Global Segment
• Label = 16000 + Index
• Advertised as index
• Distributed by ISIS/OSPF/BGP
1 2
3 4
5
16004
16004
16004
16004
16004
16004
16004
1.1.1.4/32
All nodes use default SRGB
16,000 – 23,999
BRKRST-3122 11

12. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Adjacency segment
• Forward on the IGP adjacency
• Local Segment
• Advertised as label value
• Distributed by ISIS/OSPF
• But only local adjacency SID’s are
installed in FIB!
1 2
3 4
5
24024
24025
Adj to 5
Adj to 4
All nodes use default SRGB
16,000 – 23,999
BRKRST-3122 12

13. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR operations illustration
• Steer traffic on any path through the
network
• Path is specified by list of segments
in packet header, a stack of labels
• No path is signaled
• No per-flow state is created
• IS-IS, OSPF, BGP all supported
Node Z
56056
1 3 5 7
2 4 6 8
101
Payload to Z
16101
56056
16005
Payload to Z
16101
56056
16005
Payload to Z
16101
56056
Payload to Z
16101
Payload to Z
16101
Payload to Z
Goal: Go to Z
but avoid node 7
BRKRST-3122 13

14. Incremental Deployment
Use-Cases

15. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR Innovation VPN /
Service
Transport
Topology
Independent
IP FRR
Traffic
Engineering
Egress
Peering
Engineering
Data Center
Fabric
Microloop
Avoidance
Demand
Matrix
Application
Engineered
Routing
Inter-Domain
Policy at
ScaleIncremental
Use Case
Deployment
http://blogs.cisco.com/sp/supercharge-your-network-with-segment-routing-innovations
BRKRST-3122 15

16. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR Innovation Topology
Independent
IP FRR
Traffic
Engineering
Egress
Peering
Engineering
Data Center
Fabric
Microloop
Avoidance
Demand
Matrix
Application
Engineered
Routing
Inter-Domain
Policy at
ScaleIncremental
Use Case
Deployment
VPN /
Service
Transport
http://blogs.cisco.com/sp/supercharge-your-network-with-segment-routing-innovations
BRKRST-3122 16

17. Inter-Domain Policy at Scale
draft-filsfils-spring-large-scale-interconnect

18. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Use-Case Description
• Segment Routing use-case aiming to scale the network to support hundreds of
thousands of network nodes, and tens of millions of physical underlay endpoints
• Applicable to the interconnection of massive-scale DC's and/or large
aggregation networks
• Principles are equally applicable to a network of any size
vPE1 ToR Spine LSR LSR vPE2ToRSpineLSR
DC A1 METRO A METRO BWAN DC B2
Datacenter Datacenter
Metro Metro
Core
BRKRST-3122 18

19. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SRGB and SID allocation
• Homogenous end-to-end SRGB for simplicity
• Globally Unique Prefix SIDs for devices WAN and Metro domains
• Locally Unique Prefix SIDs for Datacenters
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
20k-24k 20k-24k
17k-18k 18k-19k
16k-17k
16k-24k
BRKRST-3122 19

20. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
IGP/SR within WAN and Metro Domains
• Each domain runs ISIS/OSPF SR
• Incremental deployment and seamless interworking with LDP
DCI1
17001
LSR
17002
LSR
16003
DCI2
18001
LSR
18002
METRO A METRO BWAN
IGP / SR 2 IGP / SR 3IGP / SR 1
BRKRST-3122 20

21. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Segment Routing in the Datacenter
• Datacenter fabric runs BGP SR
• Example: 20006 is the BGP Prefix SID to DCI6
• ECMP-aware
• Simple (no LDP/RSVP)
• Policy-driven
vPE1
20001
ToR2
20002
Spine4
20004
Leaf3
20003
DCI6
20006
vPE11
20011
ToR12
20012
Spine14
20014
Leaf13
20013
Leaf15
20015
DCI16
20016
AS2
AS11
AS3 AS4 AS5 AS6AS1
Leaf5
20005
BRKRST-3122 21

22. Inter-Domain Policy at Scale
SR connectivity across domains

23. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Intra-Domain Routing – DC A1 and DC B2
• BGP SR in the DC
• Often eBGP would be used but iBGP can also be used (see tutorial)
• Smart AS (ClusterID) allocation in eBGP (iBGP) provides automated path filtering (see
tutorial)
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
vPE1/32
NH: vPE1
BGP-LU LABEL: POP
PREFIX-SID: 20001
(relative 4001)
vPE1/32
NH: TOR
BGP-LU LABEL: 20001
PREFIX-SID: 20001
(relative 4001)
vPE1/32
NH: SPINE
BGP-LU LABEL: 20001
PREFIX-SID: 20001
(relative 4001)
DCI2/32
NH: DCI2
BGP-LU LABEL: POP
PREFIX-SID: 18001
(relative 2001)
DCI2/32
NH: SPINE
BGP-LU LABEL: 18001
PREFIX-SID: 18001
(relative 2001)
DCI2/32
NH: TOR
BGP-LU LABEL: 18001
PREFIX-SID: 18001
(relative 2001)
BRKRST-3122 23

24. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Intra-Domain Routing – Metro A and Metro B
• In a metro, BGP/SR or ISIS-OSPF/SR are likely, both illustrated here
• Example: Metro A: BGP/SR
• Example: Metro B: ISIS/SR
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
DCI1/32
NH: DCI1
BGP-LU LABEL: POP
PREFIX-SID: 17001
(relative 1001)
DCI1/32
NH: LSR
BGP-LU LABEL: 17001
PREFIX-SID: 17001
(relative 1001)
ISIS LSP of AGG2
Leaf: Agg2
PREFIX-SID: 16002
(relative 2)
BRKRST-3122 24

25. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Intra-Domain Routing – WAN
• ISIS / OSPF SR in WAN
• During a migration, benefit from SR seamless interworking with LDP and ship-in-
the-night with RSVP
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
ISIS LSP of AGG1
Leaf: Agg1
PREFIX-SID: 16001
(relative 1)
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26. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Inter-Domain Routing
• WAN aggs are re-distributed down to Metro and DC
• Nothing is redistributed up !!!
• How does vPE1 reaches vPE2?
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
WAN Aggs WAN AggsWAN AggsWAN Aggs
BRKRST-3122 26

27. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Inter-Domain Routing
• Redistribution: from center to leaves
• WAN redistributes (only) its AGG’s into metro’s
• Metro redistributes (only) the WAN AGG’s into DC’s
• Redistribution: from leaves to center
• Nothing
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
ISIS LSP of AGG2
Leaf: AGG1
PREFIX-SID: 16001
(relative 1)
AGG1
NH: DCI2
BGP-LU LABEL: 16001
PREFIX-SID: 16001
(relative 1)
AGG1
NH: SPINE
BGP-LU LABEL: 16001
PREFIX-SID: 16001
(relative 1)
AGG1
NH: ToR
BGP-LU LABEL: 16001
PREFIX-SID: 16001
(relative 1)
BRKRST-3122 27

28. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Inter-Domain Routing (Cont’d)
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
ISIS LSP of AGG1
Leaf: AGG2
PREFIX-SID: 16002
(relative 2)
AGG2
NH: DCI1
BGP-LU LABEL: 16002
PREFIX-SID: 16002
(relative 2)
AGG2
NH: SPINE
BGP-LU LABEL: 16002
PREFIX-SID: 16002
(relative 2)
AGG2
NH: TOR
BGP-LU LABEL: 16002
PREFIX-SID: 16002
(relative 2)
BRKRST-3122 28

29. Inter-Domain Policy at Scale
SR PCE

30. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR PCE
• Multi-Domain topology
• Real-time reactive feed via BGP-LS/ISIS/OSPF from multiple domains
• Including ip address and SID
• Compute: stateful with native SRTE algorithms
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
Multi-Domain Topology
SR PCE
Compute
Demo
BRKRST-3122 30

31. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Circuit Optimization vs SR Optimization
2
4
1
5
3
6
7
8 9
Classic TE is circuit-based
CSPF => non-ECMP path
SID List: {4, 5, 7, 3}
Poor ECMP, big SR list, ATM optimized
2
4
1
5
3
6
7
8 9
SR-native TE algorithms needed
Recognized Innovation - Sigcomm 2015
SID List: {7, 3}
ECMP, Small SR list, IP-optimized
BRKRST-3122 31

32. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Four SR-native TE algorithms developed
• Metric optimization with inclusion/exclusion constraint and bound
• Metric: IGP metric, TE metric, extended TE-latency metric
• Inclusion/exclusion: IP address, SRLG, TE affinity, Link Loss
• Margin: any solution within the margin of the optimum is accepted
• Favor more ECMP or shorter SID list instead of insignificant optimization increment
• Also available on the router-based SRTE functionality
• Disjointness
• (A to Z) or ((A, B) to (Y, Z))
• With minimized latency diff, ECMP and shorter SID list
• (A to Z) also available on the router-based SRTE functionality
• Tactical BW optimization
• Multi-Constrained
• Sigcomm 2015 [url]
• Furthermore … TI-LFA and Microloop avoidance algorithms
BRKRST-3122 32

33. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR PCE - Fundamentally Distributed
• SR PCE not to be considered as a single “God” box
• SR PCE deployment model more like BGP Route Reflectors
• Different vPE’s can use different pairs of SR PCE’s
• SR PCE preference can either be based on proximity or service
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
SR
PCE
SR
PCE
SR
PCESR
PCE
SR
PCE
SR
PCE
SR
PCE
BRKRST-3122 33

34. Inter-Domain Policy at Scale
On-Demand SR Next Hop (ODN)

35. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Service Provisioning
• vPE1 learns about a service route with nhop vPE2
• RR shown could be any flavor of overlay controller
• How does vPE1 reach the nhop?
• vPE1 only has routes within DC A1 and to the AGG’s of the WAN domain
• Solution: On-Demand SR Next Hop (ODN)
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
BGP
RR
2: V via vPE2
VPN-LABEL: 99999
1: V via vPE2
VPN-LABEL: 99999
BRKRST-3122 35

36. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
On-Demand SR Next-Hop
Overview
• When the vPE’s does not have any RIB entry for the (locator, policy), the On-Demand SR Next-Hop
automatically sends a stateful PCEP request to the SR PCE
• Key benefit: provide the glue between the overlay and underlay controllers while decoupling them
• E.g. overlay controller does not need to react to multi-domain underlay topology change, nor compute TE policies
• E.g. underlay controller does not need to be involved in service orchestration, does not store any a priori TE policy
• E.g. no direct API or coupled workflow between the controllers
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
3: vPE2 ?
4: {SID List}
Demo
BGP
RR
2: V via vPE2
VPN-LABEL: 99999
1: V via vPE2
VPN-LABEL: 99999
BRKRST-3122 36

37. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
On-Demand SR Next-Hop
Reachability
• vPE1’s ODN functionality automatically request a solution from SR PCE
• Scalable: vPE1 only gets the inter-domain paths that it needs
• Simple: no BGP3107 pushing all routes everywhere
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
16002 vPE2
20001
ToR
20002
Spine
20003
18001LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
3: vPE2 ?
4: {16002, 18001, 20001} 2: V via vPE2
VPN-LABEL: 99999
1: V via vPE2
VPN-LABEL: 99999
Demo
BGP
RR
BRKRST-3122 37

38. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
On-Demand SR Next-Hop
SLA enabled
• Inter-domain SLA with scale and simplicity
• No RSVP, no midpoint state, no tunnel to configure !!
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
3: vPE2 with Low-
Latency?
4: {16001, 16003,
16002, 18001, 20001}
2: V via vPE2
VPN-LABEL: 99999
EXT-COM: LATENCY
1: V via vPE2
VPN-LABEL: 99999
EXT-COM: LATENCY
Demo
BGP
RR
BRKRST-3122 38

39. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Anycast SID’s for pairs of border nodes
• Anycast SID’s provide for better ECMP and High Availability
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
17901 16901 16902 18901
16902 1890117901 16901
16902 1890117901 16901
BRKRST-3122 39

40. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
On-Demand SR Next-Hop
Reachability with Anycast SID
• Better load-balancing: ECMP across border routers
• Better availability: sub-50msec upon remote aggregation router failure
• Better control plane scalability: no PCE re-computation, no PCEP update, no
FIB update
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
3: vPE2 ?
4: {16902, 18901, 20001}
16902 18901
vPE2
20001
2: V via vPE2
VPN-LABEL: 99999
1: V via vPE2
VPN-LABEL: 99999
16902 1890117901 16901
16902 1890117901 16901
BGP
RR
BRKRST-3122 40

41. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Binding SID to stitch Policies
• End-to-end policies can be composed from more basic ones
• An SRTE policy is bound by default to a Binding SID
• RSVP-TE tunnels can also be bound to a Binding SID and hence RSVP-TE tunnels can
be used within an end-to-end SR policy
• Shorter SID list and churn isolation between domains
• Even if the WAN-MetroA sub-path changes, the related Binding SID 4001 is constant
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
2: vPE2 with Min LAT?
1: REPORT {16003, 16002, 18002, 18001}, UP,
BindingSID 4001
3: REPLY {16001, 4001, 20001}
instead of
{16001, 16003, 16002, 18002, 18001, 20001}
BRKRST-3122 41

42. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Seamless Transition
• Best-effort reachability could be provided by BGP3107
• ODN and SRTE / PCE provides interdomain reachability with SLA requirements
• Eventually, migration of more/all services over SR PCE
vPE1
20001
ToR
20002
Spine
20003
LSR
17002
LSR
16003
vPE2
20001
ToR
20002
Spine
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
SR
PCE
3: vPE2 with Low Latency?
4: {16001, 16002, 18001, 20001}
BGP
RR
vPE2/32 via DCI2
PREFIX-SID: 20001
DCI2/32 via AGG2
PREFIX-SID: 18001
2:
vPE2/32 via DCI2
PREFIX-SID: 20001DCI2/32 via AGG2
PREFIX-SID: 18001
1:
BRKRST-3122 42

43. Inter-Domain Policy at Scale
Inter-Domain Disjoint Services

44. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Example: Two Disjoint Inter-domain PW’s
• ODN/SR-PCE automated compute disjoint paths for PW1 and PW2
• PW1 and PW2 do not share the same headend, neither the same tailend
• Inter-domain SLA with scale and simplicity
• No RSVP, no midpoint state, no tunnel to configure !!
SR
PCE
vPE2 disjoint group 7
{20003, 16001, 16002,
18001, 20001}
vPE22 disjoint group 7
vPE1
20001
ToR2
20002
Spine3
20003
LSR
17002
LSR
16003
vPE2
20001
ToR3
20002
Spine4
20003
LSR
18002
DC A1 METRO A METRO BWAN DC B2
vPE11
20011
ToR12
20012
Spine13
20013
vPE22
20021
ToR23
20022
Spine24
20023
{20013, 16011, 16012,
18011, 20021}
PW1
PW2
BRKRST-3122 44

45. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Example: Inter-Domain PW - Disjoint Primary / Backup paths
• ODN/SR-PCE automatically computes disjoint primary/sec paths for the PW
• sBFD runs at 3x50msec on each SRTE path
• Upon failure detection of the primary, the secondary SRTE Path is used
• Inter-domain SLA with scale and simplicity
• No RSVP, no midpoint state, no tunnel to configure !!
vPE1
20001
ToR
20002
Spine1
20003
DCI1
17001
17901
LSR
17002
AGG1
16001
16901
LSR
16003
AGG2
16002
16902
vPE2
20001
ToR
20002
Spine
20003
DCI2
18001
18901
LSR
18002
DC A1 METRO A METRO BWAN DC B2
DCI11
17011
17901
AGG11
16011
16901
AGG12
16012
16902
DCI11
18011
18901
Spine2
20004
Spine2
20004
SR
PCE1
Primary
1: Two disjoint paths to vPE2
2: PRIMARY: {17001, 16001, 16003,
18001, 20001}
SECONDARY: {17011, 16011, 16013,
18011, 20001}
Pri
Sec
BRKRST-3122 45

46. Topology Independent LFA (TI-LFA)

47. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
TI-LFA - Benefits
• 50msec Protection upon local link, node or SRLG failure
• Simple to operate and understand
• automatically computed by the router’s IGP process (ISIS and OSPF)
• 100% coverage across any topology
• predictable (backup = post convergence)
• Optimum backup path
• leverages the post-convergence path, planned to carry the traffic
• avoid any intermediate flap via alternate path
• Incremental deployment
• also protects LDP and IP traffic
BRKRST-3122 47

48. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Automated Per-Destination optimization
• 2’s computes a primary path to 5
100 100
PE4 5
2 31
6 7 8
Source
Dest2
Default metric: 10
FIB of 2 for destination 5
Incoming Label: 16005
Primary: SWAP 16005 for 16005, oif: 3
Demo
BRKRST-3122 48

49. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Flexible Link vs Node vs SRLG protection
• 2 checks the protection preference
for the primary interface of the
destination
• Link protection (illustration
assumption)
• Node protection
• SRLG protection
100 100
PE4 5
2 31
6 7 8
Source
Dest2
Default metric: 10
Demo
BRKRST-3122 49

50. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Automated and Optimum
• 2 computes the post-convergence
path if the preferred failure would
occur
• Optimality: the operator planned and
dimensioned the post-convergence
path to carry the traffic in the failure
case
• 2 uses SR to encode the post-
convergence path in a loop-free
manner
• 2 updates the FIB with the backup
path to 5
100 100
PE4 5
2 31
6 7 8
Source
Dest2
Default metric: 10
FIB of 2 for destination 5
Incoming Label: 16005
Primary: SWAP 16005 for 16005, oif: 3
Backup: SWAP 16005 for 16005, PUSH 16007, oif: 6
Demo
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51. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Do we need many SID’s? No!
BRKRST-3122 51

52. Microloop Avoidance

53. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Microloops are a day-1 IP drawback
• IP hop-by-hop routing may induce microloop at any topology transition
• Link up/down, metric up/down
Upon link down convergence
Illustration for the post-convergence microloop
impacting traffic from 1 to 9 after link45 going
down. Default link metric 10
2 3 4
5
8 7 6
1
1000
9
Pre-convergence Path
Post-convergence Path
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54. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
SR Microloop Avoidance
• Prevent any microloop upon isolated convergence due to
• link up/down event & metric increase/decrease event
• 2-stage convergence
• Stage 1: non-looping SID lists to implement the post-convergence path
• Stage 2: post-convergence path
• If multiple back-to-back convergences, fall back to native IP convergence
FIB @ 1 for Destination 9
Initially: {16009} OIF 2
Stage1: {16006, 24065, 16009}
Stage2: {16009} OIF 8
2 3 4
5
8 7 6
1
1000
9
Pre-convergence Path
Post-convergence Path
Explicit Post-convergence Path
microloop avoidance segment-routing
Demo
BRKRST-3122 54

55. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Illustration – Link Down
• No microloop can occur thanks to the 2-stage convergence and the use of non-
looping SID lists to implement the post-convergence path in stage1
2 3 4
5
8 7 6
1
Default link metric 10
1000
Pre-convergence Path
Post-convergence Path
FIB @ 1 for Destination 9
Initially: OIF to 2
Stage1: {16006, 24065, 16009}
Finally (stage2): OIF 8
9
FIB @ 8 for Destination 9
Initially: OIF to 1
Stage1: {16006, 24065, 16009}
Finally (stage2): OIF 7
FIB @ 7 for Destination 9
Initially: OIF to 8
Stage1: {16006, 24065, 16009}
Finally (stage2): OIF 6
FIB @ 6 for Destination 9
Initially: OIF to 7
Stage1: {24065, 16009}
Finally (stage2): OIF 5
Illustration for the post-convergence
microloop impacting traffic from 1 to 9
after link45 going down
Demo
BRKRST-3122 55

56. Conclusion

57. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Conclusion
• Functionality never seen before
• SR is fundamental architecture for modern IP network
• Unified Fabric with Policy through DC, Metro and WAN
• Simplification through Automation and protocol removal
• Strong operator endorsement
• Multi vendor consensus
• Impressive deployment and velocity
BRKRST-3122 57

58. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Resources
• Stay Informed - Tutorials, Conferences, IETF, Open-source SW
• http://www.segment-routing.net/
• Join us – Segment Routing @ LinkedIN
• Get in Touch
• ask-segment-routing@cisco.com
• “Latest” SR Demonstrations
• On-demand Next-Hop and SR PCE
• TI-LFA Node protection
• Microloop Avoidance
• SRv6 “Spray” use-case
• Segment Routing book
• Pre-order available now!
BRKRST-3122 58

59. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Complete Your Online Session Evaluation
Don’t forget: Cisco Live sessions will be available
for viewing on-demand after the event at
CiscoLive.com/Online
• Give us your feedback to be
entered into a Daily Survey
Drawing. A daily winner will
receive a $750 Amazon gift card.
• Complete your session surveys
through the Cisco Live mobile
app or from the Session Catalog
on CiscoLive.com/us.
BRKRST-3122 59

60. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Continue Your Education
• Demos in the Cisco campus
• Walk-in Self-Paced Labs
• Lunch & Learn
• Meet the Engineer 1:1 meetings
• Related sessions…
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61. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Public
Segment Routing opportunities at CiscoLive!
• BRKRST-2124: Introduction to Segment Routing
• Presented Monday – view session materials on CiscoLive.com
• LABSPG-2012: Next Generation Service Provider Network using Segment
Routing & BIER
• In the Walk-in Self-Paced (WISP) lab area of the hub until 5pm today!
• BRKDCN-2050: Segment Routing in Datacenter using Nexus 9000 and 3000
• At 1pm today! South Pacific B, Lower Level
• LTRMPL-2104: Cisco WAN Automation Engine (WAE) Network
Programmability with Segment Routing
BRKRST-3122 61

62. Thank you