1. Segment Routing Traffic Engineering
Diptanshu Singh

2. Why Traffic Engineering ?
High bandwidth paths
Low Latency paths
Disjoint paths
Avoid resources
avoid low bandwidth links
avoid high utilized links
Optimize Network Capacity
Ad-Hoc
Calendaring

3. Distributed or Centralized computing ?
Policy
Single-Domain
Multi-Domain
Reachability
IGP’s
Centralized
Low Latency
Distributed or Centralized
Disjoin from same node
Disjoin from different node
Avoiding resources
Capacity optimization
Low Priority
Others…
TBD

4. High level Architecture
SR PCE have multi-domain topology view
--feed via BGP-LS from multiple domains
Stateful PCE with native SRTE algorithms.
PCEP Messages:
PCEP Request (PCC -> PCE)
PCEP Reply (PCE -> PCC)
PCC Report (PCC -> PCE)
PCE Update (PCE -> PCC)
PCE Initiate (PCE -> PCC)
PCE controller
LSP-DB
TED
PCEP
BGP-LS
BGP-LS
Router
PCC
Router
Area Y
Area X
Router
Area Z
Router

5. SR Basics: Binding Segment
Binding Segment represents a tunnel at SR
The Binding Segment is a local segment
Has local significance
A Binding-Segment ID identifies a SRTE Policy
Each SRTE Policy is associated 1-for-1 with a Binding-SID
Packets received with Binding-SID as top label are steered into the SRTE Policy associated with the Binding-SID
Binding-SID label is popped, SRTE Policy’s SID list is pushed

6. SR Basics: Binding Segment
Binding-SID use-case examples:
Label stack “compression”: nesting and stitching SRTE Policies
BGP SRTE Dynamic: use local Binding-SID(later)
PCEP Request
Could you provide me the ERO for AC1?
PCE controller 2 3
PCC Report
17002,17003,17004
Binding SID 4001
PCEP Reply
17001,4001
Instead of 17001,17002,17003,17004 1
WAN DC
TOR
WAN
Headend
AC1 IP
4001
Unicast-SID 17002 IP
17004
17003 IP
Unicast-SID 17001
Unicast-SID 17003 IP
17004
Unicast-SID 17004 IP
4001
17001 IP
17004
17003
17002

7. Segment Routing Traffic Engineering:
On Demand Next Hop
BGP SR-TE dynamic
HA with PCE SR controller

8. On demand SR Next Hop DC WAN Access BGP Link State
Unicast-SID 17001
Anycast-SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast-SID 17002
Unicast-SID 17003
Anycast-SID 18002
Unicast-SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Including ip address and SID
BGP Route Reflector
BGP Link State
ISIS SR2
SRGB
ISIS SR1
SRGB 17k-18k
ISIS SR3
SRGB

9. On demand SR Next Hop DC WAN Access Service Orchestrator
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
XML YANG:
PW-123 from ToR1 to AC1
BGP Route Reflector
XML YANG:
PW-123 from AC1 to ToR1

10. On demand SR Next Hop DC WAN Access Service Orchestrator
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
NMS/OSS to configure service
ToR1 check if he has LSP to AC1
Yes -> use it
No -> next slide
Do I have LSP
to AC1 ?
BGP Route Reflector

11. On demand SR Next Hop DC WAN Access Service Orchestrator
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
ToR1 check if he has LSP to AC1
ToR1 request LSP to PCE
PCEP request
- Could you provide me the ERO to reach AC1 ?
BGP Route Reflector 1
PCEP reply
ERO is: 18001,18002,16001 2 3

12. On demand SR Next Hop DC WAN Access Service Orchestrator
Unicast-SID 17001
Anycast-SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast-SID 17002
Unicast-SID 17003
Anycast-SID 18002
Unicast-SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
ToR1 check if he has LSP to AC1
ToR1 request LSP to PCE
ToR1 report service state to orchestrator
XML YANG notification:
PW-123 is UP
BGP Route Reflector
Ethernet
Ethernet
Ethernet PW
16001
18002
18001
Ethernet PW
16001
18002
Ethernet PW
16001

13. ODN with policy DC WAN Access Service Orchestrator PCE controller
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
XML YANG:
PW-123 from ToR1 to AC1
PW-124 from ToR2 to AC2
Policy: Disjoin GID 123
BGP Route Reflector
XML YANG:
PW-123 from AC1 to ToR1
PW-124 from AC2 to ToR2
Policy: Disjoin GID 123

14. ODN with policy DC WAN Access Service Orchestrator PCE controller
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
ToR1 and ToR2 check if they has LSP to AC1 and AC2 respectively.
ToR1 and ToR2 request LSP to PCE
PCEP request
Could you provide me the ERO to reach AC1 ?
Policies are G-ID 123
BGP Route Reflector
PCEP request
Could you provide me the ERO to reach AC2 ?
Policies are G-ID 123 1 2

15. ODN with policy (Cont) DC WAN Access Service Orchestrator
Unicast SID 17001
Anycast SID 18001
Unicast-SID 16001
Service Orchestrator
Unicast SID 17002
Unicast SID 17003
Anycast SID 18002
Unicast SID 17004
ToR1
ToR2
ABR1
ABR2
ABR3
ABR4
AC1
Unicast-SID 16002
PCE controller
AC2
Hint:
PCE collect topology and SID via BGP LS
Service Orchestrator to configure service
ToR1 and ToR2 check if they has LSP to AC1 and AC2 respectively.
ToR1 and ToR2 request LSP to PCE
PCE sees the same Disjoint ID and computes two Disjoint paths 3
BGP Route Reflector
PCEP reply
ERO is: 17001,17003,16001 4
PCEP reply
ERO is: 17002,17004,16002
Ethernet PW
16001
17003
17001
Ethernet PW
16001
17003
Ethernet PW
16001
Ethernet PW
16002
17004
17002
Ethernet PW
16002
17004
Ethernet PW
16002

16. On demand steering for BGP services
Technical name: BGP SR-TE dynamic
Hint:
Isolated domains with no redistribution.
CPE send BGP update for prefix X and add LL community ex: 100:777
PCE controller
BGP Route Reflector
BGP-LS
BGP-LS
L3VPN
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
BGP-LS
Unicast-SID 16001
CPE1
ToR1
ABR1
ABR3
AC1
CPE2 DC
WAN
Access
ToR2
ABR2
ABR4
AC2
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

17. On demand steering for BGP services
Technical name: BGP SR-TE dynamic
Hint:
Isolated domains with no redistribution.
CPE send BGP update for prefix X and add LL community ex: 100:777
PCE controller
BGP Route Reflector
L3VPN
NLRI: /32
Community: 100:777
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
Unicast-SID 16001
CPE1
ToR1
ABR1
ABR3
AC1
CPE2 DC
WAN
Access
ToR2
ABR2
ABR4
AC2
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

18. On demand steering for BGP services
Technical name: BGP SR-TE dynamic
Hint:
CPE send BGP update for prefix X and add LL community
AC1 PE announce VPN prefix X with LL community
PCE controller
BGP Route Reflector
L3VPN
NLRI: /32
Community: 100:777
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
Unicast-SID 16001
CPE1
ToR1
ABR1
ABR3
AC1
CPE2 DC
WAN
Access
ToR2
ABR2
ABR4
AC2
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

19. On demand steering for BGP services
Technical name: BGP SR-TE dynamic
Hint:
CPE send BGP update for prefix X and add LL community
AC1 PE announce VPN prefix X with LL community
On demand Next Hop LL to PCE controller
Install explicit path for prefix X in VRF
PCE controller
PCEP request
Could you provide me the ERO to reach AC1 ?
Policy is LL
BGP Route Reflector 1
PCEP reply
ERO is: 17001,17003,16001 2
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
Unicast-SID 16001
CPE1
ToR1
ABR1
ABR3
AC1
CPE2 3 DC
WAN
Access
ToR2
ABR2
ABR4
AC2
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

20. On demand steering for BGP services
TE installs SRTE Policy in FIB:
Binding-SID (e.g ): push {Label 17001, Label ,Label 16001}
TE provides the Binding-SID of the SRTE Policy to BGP
BGP
/32; NH: AC1
Received VPN label: L_VPN
Community 100:777
Binding Label: 24006 TE
SRTE Policy to AC1:
SID List {17001,17003,16001},OIF 3
Binding Label: 24006
FIB
Local label: out label: POP
OIF: SRTE; Label stack { }

21. On demand steering for BGP services
RIB installs in FIB:
/32 via 24006
Push VPN label and steer in SRTE Policy
TE installs SRTE in FIB
BGP, RIB and FIB aware of BSID
BGP
/32; NH: AC1
Received VPN label: L_VPN
Community 100:777
Binding Label: 24006 TE
SRTE Policy to AC1:
SID List {17001,17003,16001},OIF 3
Binding Label: 24006
FIB
/32; recursion-via-label
label L_VPN, NH via 24006
Local label: out label: POP
OIF: SRTE; Label stack { }

22. PCE HA DC WAN Access PCE2 Secondary PCE1 Primary BGP Route Reflector
Service Provisioned via Overlay RR,Orchestrator
Request via PCEP to PCE primary with TE policy
PCE replies with ERO 17001,17003,16001
ToR1 Reports to PCE Primary and Secondary via PCC Report
Primary PCE fails
ToR1 waits for some time
ToR1 Reports PCE2 of becoming master 5
PCE2 Secondary
PCE1 Primary 2 3 4 7
BGP Route Reflector 1
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
Unicast-SID 16001
CPE1
ToR1
ABR1
ABR3
AC1
CPE2
6: wait for
some timer DC
WAN
Access
ToR2
ABR2
ABR4
AC2
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

23. ODN HA model DC Access WAN Service Orchestrator PCEP BGP LS PCEP CPE1
SR-PCE not to be considered as a Single “god” box
SR-PCE is closer to RR
Different TOR’s can use different pairs of SR-PCE
SR PCE preference can be either based on proximity or service
Service Orchestrator
Unicast SID 17001
Anycast SID 18001
Unicast SID 17003
Anycast SID 18002
Unicast-SID 16001
Unicast-SID 16001
CPE1
ToR1
PCEP
ABR1
BGP LS
ABR3
PCE
PCEP
AC1
CPE2
PCE RR RR DC
Access
WAN
ToR2
ABR2
PCE
ABR4
PCE
AC2 RR RR
Unicast-SID 16002
Unicast SID 17002
Anycast SID 18001
Unicast SID 17004
Anycast SID 18002
Unicast-SID 16002

25. References http://www.segment-routing.net/ Current IETF Drafts for SR:
PCEP Extensions for Segment Routing
Binding SID
Anycast Segments in MPLS based Segment Routing
BGP Link-State extensions for Segment Routing