![LDP & RSVP-TE
A
B D
C E
F A
B D
C E
F
▪ Label distribution protocol by piggybacking IGP
▪ LDP session between routers to exchange labels
▪ Labels are locally significant
▪ Does not support link characteristics
▪ IGP-based, supports ECMP
▪ Flexible but limited functionality
▪ Reservation protocol used to reserve Path
▪ Reserving: label, ERO, SERO, BW
▪ RSVP Session for every [Dest, Src] pair
▪ n*(n-1) issue
▪ Routers keep track BW usage
▪ Inflexible but Powerful
LDP RSVP-TE
Segment Routing: Powerful and Flexible
LDP
LDP
LDP
PATH Descriptor
RESV Descriptor](https://image.slidesharecdn.com/segmentrouting-170703200834/85/Segment-Routing-for-Dummies-5-320.jpg)
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Segment Routing for Dummies
- 1. Segment Routing Primer AnRSVP-TE/LDP Revolution Just for Fun: Gary Jan
- 2. Content ▪ Introduction ▪ Architecture ▪LDP & RSVP-TE ▪ Segment Routing- IGP Walkthrough ▪ Segment Routing- Explicit Path Walkthrough
- 3. Introduction ▪ Segment Routing ▪Source-based routing solution ▪ Embedding instructions as “Segments” in the packet ▪ Formless, Shapeless, Stateless ▪ Removes complexity (signaling, session, etc) in the network ▪ History ▪ Cisco driven. First introduced in IETF in 2013. IETF accepted in 2014 ▪ Vendor specific commercial solutions since 2015 ▪ https://tools.ietf.org/html/draft-ietf-spring-segment-routing-11
- 4. Segment Routing- Architecture ForwardingPlane Control Plane Service Plane MPLS IPv6 OSPF/ISIS BGP PCC TE FRR ECMP PCE Service Plane ▪ Keeping all service diversity Control Plane ▪ OSPF/ISIS/BGP extension to advertise Segment information Forwarding Plane ▪ Reuse MPLS and IPv6 Keep the good stuff; Remove the tedious stuff
- 5. LDP & RSVP-TE A BD C E F A B D C E F ▪ Label distribution protocol by piggybacking IGP ▪ LDP session between routers to exchange labels ▪ Labels are locally significant ▪ Does not support link characteristics ▪ IGP-based, supports ECMP ▪ Flexible but limited functionality ▪ Reservation protocol used to reserve Path ▪ Reserving: label, ERO, SERO, BW ▪ RSVP Session for every [Dest, Src] pair ▪ n*(n-1) issue ▪ Routers keep track BW usage ▪ Inflexible but Powerful LDP RSVP-TE Segment Routing: Powerful and Flexible LDP LDP LDP PATH Descriptor RESV Descriptor
- 6. Segment Routing- Jargons ▪Segment ID (SID) ▪ Identifier of instruction ▪ Prefix SID ▪ Shortest path to an IP prefix ▪ Node SID ▪ Shortest path to a node ▪ Adjacency SID ▪ Instruction to use a link ▪ Instruction to apply local services A B D C E F IP Subnet Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300
- 7. Route / FIBDevelopment 1. SR routers use OSPF/ISIS/BGP to advertise routers and SIDs 2. Eventually, LSDB in every SR router of the network has full topology info ▪ Distance to every prefix, subnet ▪ Segments IDs of every node, link, and prefix ▪ Bandwidth ▪ FIB, and TED 3. Path computation ▪ Distributed: PCE in routers populate FIB ▪ Centralized: PCE in SDN populates FIB through BGS-LS Segment Routing: Powerful and Flexible
- 8. Example- FIB 1/2 RouteTable of A Destination Segment ID Interface 10.1.0.0/16 6000 A-B / A-C ........ …….. …….. A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 FIB of A In SID Action Out SID Interface 6000 Swap 6000 A-B / A-C 600 Swap 600 A-B/ A-C 400 Swap 400 A-C 101 Pop - A-C FIB of B In SID Action Out SID Interface 6000 Swap 6000 B-D 400 Pop - B-D
- 9. Example- FIB 2/2 A BD C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 FIB of E In SID Action Out SID Interface 6000 Swap 6000 E-F 600 Pop - E-F 100 Swap 100 E-C FIB of D In SID Action Out SID Interface 6000 Swap 6000 D-F 401 Pop - D-E 600 Pop - D-F 100 Pop - D-B FIB of F In SID Action Out SID Interface 6000 Pop - F
- 10. Packet Walkthrough- IGP1/2 A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 6000 10.1.1.1/16 Src IP Payload 10.1.1.1/16 Src IP Payload Route Table of A Destination Segment ID Interface 10.1.0.0/16 6000 A-B / A-C ........ …….. …….. FIB of A In SID Action Out SID Interface 6000 Swap 6000 A-B / A-C 600 Swap 600 A-B/ A-C 500 Swap 500 A-C 101 Pop - A-C
- 11. Packet Walkthrough- IGP2/2 A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 6000 10.1.1.1/16 Src IP Payload FIB of B In SID Action Out SID Interface 6000 Swap 6000 B-D ........ …….. …….. 6000 10.1.1.1/16 Src IP Payload FIB of D In SID Action Out SID Interface 6000 Swap 6000 D-F 401 Pop - D-E 600 Pop - D-F 100 Pop - D-B FIB of F In SID Action Out SID Interface 6000 Pop - F 6000 10.1.1.1/16 Src IP Payload 10.1.1.1/16 Src IP Payload
- 12. Explicit Path- SR-TE ▪What if I want to use path ABDEF ▪ Explicit Path- PCE ▪ SR-TE- IGP ▪ SR-TE- PCE A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602
- 13. Explicit Path- ControllerPCE 1/2 ▪ Pkt with dest. IP 10.1.1.1/16 ingress A ▪ Router A request SDN controller Segment instructions through Netconf/Yang ▪ Controller instructs Segments/Labels ▪ Note, Label FIB in the network remain unchanged A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602400 401 500 600 6000 10.1.1.1/16 Src IP Payload 10.1.1.1/16 Src IP Payload FIB of A In SID Action Out SID Interface 6000 Swap 6000 A-B / A-C 600 Swap 600 A-B/ A-C 400 Swap 400 A-B/ A-C 101 Pop - A-C OSS
- 14. Explicit Path- ControllerPCE 2/2 A B D C E F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 400 401 500 600 6000 10.1.1.1/16 Src IP Payload FIB of B In SID Action Out SID Interface 6000 Swap 6000 B-D 400 Pop - B-D FIB of D In SID Action Out SID Interface 6000 Swap 6000 D-F 401 Pop - D-E 600 Pop - D-F 100 Pop - D-B 401 500 600 6000 10.1.1.1/16 Src IP Payload 500 600 6000 10.1.1.1/16 Src IP Payload OSS
- 15. SR-TE- PCE A B D CE F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 400 401 500 600 6000 10.1.1.1/16 Src IP Payload 401 500 600 6000 10.1.1.1/16 Src IP Payload 500 600 6000 10.1.1.1/16 Src IP Payload 600 6000 10.1.1.1/16 Src IP Payload 6000 10.1.1.1/16 Src IP Payload OSS Controller distribute segment instructions to every node on the path
- 16. SR-TE- IGP A B D CE F IP Subnet 10.1.0.0/16 Node SID 200 Node SID 500 Node SID 100 101 301 Adjacency SID Prefix SID 6000Node SID 300 Node SID 400 Node SID 600 401 501 502 602 400 401 500 600 6000 10.1.1.1/16 Src IP Payload 401 500 600 6000 10.1.1.1/16 Src IP Payload 500 600 6000 10.1.1.1/16 Src IP Payload 600 6000 10.1.1.1/16 Src IP Payload 6000 10.1.1.1/16 Src IP Payload OSS Controller distribute segment instructions to Head of Path. Head reserve path by using IGP extension. IGP
- 17. My few cents ▪MPLS transition to SR will be an issue since non-duplication of label space ▪ Segment routing reduces the complexity of label distribution ▪ However, it doesn’t solve the complexity of the network ▪ Segment routing still heavily relying on IGP or BGP to flood the network topology ▪ Inherently the drawbacks of IGP
- 18.