SDN Workshop. Contact: WSDN01_v0.1

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1 SDN Workshop Contact: WSDN01_v0.1 Issue Date: [Date] Revision: [xx]

2 Segment Routing SDN Workshop WSDN01_v0.1 Issue Date: [Date] Revision: [xx]

3 Overview In a nutshell Introduction to MPLS Segment Routing Introduction Architecture MPLS data plane IPv6 data plane BGP EPE LDP inter-working 3

4 In a nutshell 4

5 SDN architectural framework Application Plane Northbound Interfaces Application Service REST/RESTCONF/NETCONF/XMPP Network Services Abstraction Layer Control Plane (controller) Topology Discovery & Management Route selection & failover Traffic Engineering Resource Management Configuration East/Westbound interfaces BGP Southbound Interfaces BGP-LS i2rs PCE-P ForCES IPFIX SNMP Open Flow Netconf BGP RIBs PCC SNMP MIBs OpenFlow YANG Data Plane Segment Routing RSVP- TE Device & Resource Abstraction Layer (DAL) Network Devices IP/MPLS/Transport Note: designations of north-bound and south-bound are relative to the control plane ( controller ) 5

6 Segment routing: in a nutshell What? The source determines the path a packet should take How? By encoding the path within the packet as a sequence of segments or instructions. Why? To reduce network state and allow centralised computation of paths 6

7 MPLS Introduction 7

8 Introduction MPLS: Multi-Protocol Label Switching Tunneling mechanism that supports a number of types of payloads (hence multi ) Concept of Forwarding Equivalence Class (FEC): groups of packets that need to be forwarded in an identical manner. Each FEC is assigned a label, a 20-bit opaque value Packets are classified into FECs at network ingress and an MPLS label corresponding to the FEC is added to the packet Intermediate hops swap the MPLS label and forward the packet onwards to their next-hops 8

9 MPLS label stack entry Transport IP MPLS Shim Header Data Link Layer encapsulation LER LSR 9

10 MPLS label operations PUSH: Adds a new label to the label stack (which may be empty) SWAP: Acts on the top (outer) label Replaces the top label value with another label value POP: Removes the top label, exposing either another label or the payload of the MPLS packet 10

11 MPLS tables NHLFE (Next Hop Label Forwarding Entry): Used for forwarding labeled packets Contains next-hop, label operation, link-layer encapsulation information ILM (Incoming Label Map): Mapping between incoming labels and NHLFEs FEC to NHLFE map (FTN): Used for forwarding unlabeled packets Maps each FEC to a set of NHLFEs 11

12 MPLS node types LSR LSR LSR iler Ingress Label Edge Router (iler) MPLS router that pushes MPLS label LSR LSR LSR eler Egress Label Edge Router (eler) MPLS router that pops MPLS label Label Switch Path Path taken by MPLS packets from iler to eler Label Switch Router (LSR) MPLS router that swaps MPLS label 12

13 MPLS VPN node types P P P PE PE Provider Edge VPN LER Provider Edge VPN LER P P P Label Switch Path Path taken by MPLS packets from PE to PE Provider Router (P) LSR in an MPLS VPN network 13

14 BGP/MPLS: service (VPN) label exchange P1 P2 P3 CE1 BGP-MPLS PE1 FEC: VPN-X PE2 CE2 Label: P4 P5 Metric: 100 P All IGP metrics are equal to 10 unless otherwise indicated 14

15 LDP: building the ILM ILM Outlabel Inlabel Outlabel Intf To-P2 ILM Inlabel Intf To-P3 ILM In-label Out-label Interface To-PE2 P1 P2 P3 ILM In-label Out-label Interface CE1 LDP FEC: PE2 Label: 300 LDP FEC: PE2 Label: 200 LDP FEC: PE2 FEC: PE2 Label: 400 LDP Label: FEC: PE2 Label: Local PE1 LDP PE2 CE2 FTN FEC Outlabel Intf PE To-P1 P4 P5 Metric: 100 P ILM Inlabel Outlabel Intf All IGP metrics are equal to 10 unless otherwise indicated To-P2 15

16 LDP: traffic forwarding Swap 400 for P1 300 Swap 300 for 200 P2 200 Swap 200 for 100 P CE1 PE1 PUSH 1234, 400 POP 100, 1234 PE2 CE P4 P5 Metric: 100 P6 Packet destined to PE2 arrives at PE All IGP metrics are equal to 10 unless otherwise indicated 16

17 LDP: building the ILM (with PHP) ILM Intf To-P2 ILM Intf To-P3 ILM In-label Out-label Interface To-PE2 P1 P2 P3 CE1 LDP FEC: PE2 Label: 300 LDP FEC: PE2 Label: 200 LDP FEC: PE2 FEC: PE2 Label: 400 LDP Label: 3 (implicit null) FEC: PE Label: 300 PE1 LDP PE2 CE2 FTN FEC Outlabel Outlabel Intf PE To-P1 P4 P5 P ILM Inlabel Outlabel Inlabel Outlabel Inlabel Intf To-P2 Metric: 100 PHP: Penultimate Hop Pop All IGP metrics are equal to 10 unless otherwise indicated 17

18 LDP: traffic forwarding (with PHP) Swap 400 for P1 300 Swap 300 for 200 Pop P2 P CE1 PE1 PUSH 1234, 400 POP 1234 PE2 CE P4 P5 Metric: 100 P6 Packet destined to PE2 arrives at PE All IGP metrics are equal to 10 unless otherwise indicated 18

19 LDP: observations LDP forwarding follows the IGP shortest paths All nodes install an ILM entry for every LDP destination A single LDP label (associated with the destination) is required to transport packets Labels are assigned by the downstream routers i.e. the label a router uses for ILM lookup is that assigned by the router itself LDP label changes at each hop as labels are locallysignificant 19

20 RSVP-TE: signaling an LSP (1) RSVP-TE Msg: PATH Dest: PE RSVP-TE Msg: PATH Dest: PE2 P1 P2 P3 CE1 RSVP-TE Msg: PATH RSVP-TE Dest: PE2 Msg: PATH Dest: PE PE1 PE2 CE2 P4 P5 Metric: 100 P RSVP-TE Msg: PATH Dest: PE2 All IGP metrics are equal to 10 unless otherwise indicated 20

21 RSVP-TE: signaling an LSP (2) ILM Intf To-P2 ILM Intf To-P5 P1 P2 P3 ILM In-label Out-label Interface CE1 FTN FEC PE1 RSVP-TE PE2 CE2 P4 RSVP-TE Msg: RESV Label: 666 Intf LSP1 555 To-P1 Msg: RESV Label: 777 P5 ILM P RSVP-TE Msg: RESV Label: 888 Inlabel Outlabel Inlabel Outlabel Outlabel In- Msg: RESV label label Label: 555 RSVP-TE To-PE Out- Metric: 100 Intf RSVP-TE Msg: RESV Label: POP Local ILM Inlabel Outlabel Intf All IGP metrics are equal to 10 unless otherwise indicated To-P6 21

22 RSVP-TE: traffic forwarding Swap 555 for P1 666 Swap 666 for 777 P2 P3 CE1 Packet mapped to LSP1 PUSH 1234, PE POP PE2 CE , P4 777 P5 P Swap 777 for 888 Metric: 100 Swap 888 for All IGP metrics are equal to 10 unless otherwise indicated 22

23 RSVP-TE: observations RSVP-TE allows the construction of arbitrary paths based on traffic-engineering requirements i.e. longer IGP paths may end up being preferred For two nodes to communicate, RSVP-TE LSPs need to be signaled in both directions. RSVP-TE maintains soft-state which needs to be refreshed periodically RSVP-TE label changes at each hop as labels are locallysignificant 23

24 MPLS label distribution protocols Attribute LDP RSVP-TE BGP Relative Complexity Low High Medium Application Shortest-path routing Traffic engineering Scaling (seamless MPLS) Label allocation (unicast) Multipoint-to-point Point-to-point Point-to-point Label significance Local Local Local Multicast mldp extensions p2mp LSPs N/A Traffic-engineering No Yes No Fast Reroute (FRR) Yes (xlfa extensions) Yes Yes (BGP PIC) FRR coverage Scaling Usually <100% via xlfa but not guaranteed O(n) One LSP per destination 100% via link and node protection O(n^2) Full-mesh required for complete coverage IGP interaction Dependent Required for TE extensions Limited to BGP PIC O(n) One LSP per destination N/A 24

25 Challenges How do we achieved fine-grained traffic-engineering at scale? RSVP-TE faces scaling challenges due to it s connected-oriented meshing requirement LDP does not have traffic-engineering capabilities We need a mechanism that marries the best of RSVP-TE with the best of LDP 25

26 Segment Routing introduction 26

27 Standardisation Defined by the SPRING (Source Packet Routing in Networking) in working group of the IETF The ability for a node to specify a forwarding path, other than the normal shortest path, that a particular packet will traverse, benefits a number of network functions: Some types of network virtualization, including multi-topology networks and the partitioning of network resources for VPNs Network, link, path, and node protection such as fast reroute Network programmability OAM techniques Simplification and reduction of network signaling components Load balancing and traffic engineering 27

28 Requirements MUST allow incremental and selective deployment without requiring a flag day or massive upgrade of all network elements MUST allow putting policy state in the packet header and not in the intermediate nodes along the path i.e. there should be no policy state in mid-points and tail-ends. 28

29 Source Routing Segment Routing leverages the concept of Source Routing, where the source of the packet includes routing information within the data packet itself. Contrast this with hop-by-hop destination-based routing, where each intermediate point makes a determination of how a packet needs to be forwarded Supported data planes: MPLS without any modification (this section focusses chiefly on the MPLS data plane) IPv6 with the use of a new IPv6 Routing Header type 29

30 How it works The source determines the path a packet should take and encodes it within the packet as a sequence of segments or instructions. For routing purposes, segments are topological instructions: node: take shortest path to the node adjacency: send packet over the specified adjacency regardless of IGP metric Intermediate hops inspect the segment list and route as per the instructions implied by it; no per-path state is kept 30

31 Use case: IGP-based MPLS tunneling PE1 installs prefix Z in VRF for VPN-X and resolves nexthop to PE2 via an IGP-based P1 P2 MPLS tunnel to PE2 Route to Z MP-BGP: VPN-X, route to Z, A CE1 PE1 label LZ, next-hop PE2 PE2 CE2 Z VPN-X P3 P4 VPN-X 31

32 Use case: Fast Reroute (FRR) Support of FRR on any topology Precomputation and setup of backup path without any additional signaling (other than the regular IGP/BGP protocols) Support of shared risk constraints Support of node and link protection Support of micro-loop avoidance 32

33 Use case: traffic engineering Loose or strict options Bandwidth admission control Distributed vs. centralized model Disjointness in dual-plane networks Egress peer engineering Load balancing among non-parallel links (i.e., links connected to different adjacent neighbors). Limiting (scalable, preferably zero) per-service state and signaling on midpoint and tail-end routers. ECMP-awareness 33

34 Sneak preview: SR-TE example Routing: Traffic-engineered. The link from PE5 to PE6 has a link-metric of 100. How do we force traffic over this link? Segments Identifiers: Node and Adjacency segments 34

35 Objectives Objectives: All traffic from PE1 to PE2 should traverse P2 but avoid the P2- P3 link P1 P2 P3 CE1 PE1 PE2 CE2 P4 P5 Metric: 100 P6 All IGP metrics are equal to 10 unless otherwise indicated 35

36 Traffic forwarding Node P2 CE1 Node P2 Node P5 P5-P6 link Node PE2 VPN X Node P5 P5-P6 link Node PE2 VPN X P1 P2 P3 Node P5 P5-P6 link PE2 PE1 VPN X VPN X PE2 CE2 PE2 VPN X PE2 P4 P5 Metric: 100 P6 All IGP metrics are equal to 10 unless otherwise indicated 36

37 Architecture 37

38 Introduction Segment Routing (SR) allows a node to steer a packet through an ordered list of instructions, called segments. Segments can represent any type of instruction: Topological Service Application Etc. Semantics of a segment can be local to an SR node or global within the SR domain Allows steering of flows without requiring per-flow state at intermediate points in the network 38

39 Terminology (1) Segment an instruction a node executes on an incoming packet. For example: forward packet according to shortest path to destination, or forward packet through a specific interface, or deliver the packet to a given application/service instance Global Segment The related instruction is supported by all SR-capable routers in the domain 39

40 Terminology (2) Local Segment The related instruction is only supported by the router originating it Segment Identifier (SID) identifier for a segment. Current options include: An absolute MPLS label value An index value in an MPLS label space An IPv6 address 40

41 Terminology (3) Segment List an ordered list of SIDs encoding the ordered set of instructions to be applied to a packet as it traverses an SR domain. In an MPLS data plane, the Segment List is instantiated as a stack of labels. In an IPv6 data plane, it is instantiated as an ordered list of IPv6 addresses. Segment Routing Domain (SR Domain) the set of nodes participating in the source-based routing model 41

42 Terminology (4) SR Global Block (SRGB) set of local MPLS labels reserved for global segments. Segment List Depth The number of segments in a segment list 42

43 Segment list (1) An ordered list of SIDs encoding the ordered set of instructions to be applied to a packet as it traverses an SR domain. In an MPLS data plane, the Segment List is instantiated as a stack of labels. In an IPv6 data plane, it is instantiated as an ordered list of IPv6 addresses. The Active Segment that must be used by the receiving router to process the packet is: The top label in the MPLS dataplane The destination address of a packet with a Segment Routing Header (SRH) in the IPv6 dataplane 43

44 Segment list (2) The segment list imposed by the SR node at the edge of the SR domain can be computed either: locally by an operator provisioned via NETCONF provisioned via PCE-P 44

45 IGP segments IGP Segments Segments identifying information advertised by an IGP IGP-Prefix Segments Global (Prefix-SID) Segment representing an IGP prefix IGP-Adjacency Segments Local (Adjacency-SID) Segment representing an IGP adjacency Semantics: SR header operation: NEXT Next-hop: related egress interface IGP-Anycast Segments Global (Anycast-SID) Segment representing an anycast prefix IGP-Node Segments Global (Node-SID) Segment identifying a specific router Remote-Binding Segment Global (Binding-SID) Advertised by a Mapping Server for prefixes attached to non-sr routers 45

46 Node SIDs Node SIDs are used to identify nodes as destinations Globally significant, by default Nodes-SIDs are essentially instructions to forward a packet via the shortest ECMP-aware IGP path to the destination node Advertised by the link-state IGP (OSPF, IS-IS) Need to be manually configured 46

47 Anycast SIDs A SID that is advertised by all the members of an Anycast set All routers in the set advertise the same Anycast prefix and SID value Globally significant, by default Anycast-SIDs are essentially instructions to forward a packet via the shortest ECMP-aware IGP path to the topologically closest member of the Anycast set Advertised by the link-state IGP (OSPF, IS-IS) 47

48 Adjacency SIDs Nodes allocate one Adj-SID for each of its adjacencies Nodes may allocate multiple Adj-SIDs to the same adjacency A node may allocate the same Adj-SID to multiple adjacencies: Packets containing such an Adj-SID are then hashed across the different adjacencies Locally significant, by default, and is installed only in the FIB of the originating router Adj-SIDs are essentially instructions to forward a packet out a specific interface regardless of IGP link metric Advertised by the link-state IGP (OSPF, IS-IS) 48

49 BGP peering segments An ingress border router of an AS can steer a flow along a selected AS, towards a selected egress border router of the AS and through a specific peer by using BGP Egress Peer Engineering capabilities BGP Peering Segments Segments identifying by a BGP EPE (Egress Peer Engineering)-enabled node. Enable the expression of source-routed interdomain paths Peer Node Segments Local (PeerNode-SID) Segment representing a BGP peering node Semantics: SR header operation: NEXT Next-hop: connected peering node to which the segment is related Peer Adjacency Segments Local (PeerAdj-SID) Segment representing an adjacency to a BGP peering node Semantics: SR header operation: NEXT Next-hop: peer connected through the interface to which the segment is related Peer Set Segments Local (PeerSet-SID) Segment representing a set of BGP peering nodes Semantics: SR header operation: NEXT Next-hop: load-balance across any connected interface to any peer in the related group 49

50 Segment operations Operation Segment Routing semantic MPLS data plane IPv6 data plane PUSH Insertion of a segment at the top of the segment list PUSHing a new label on to the label stack Setting of the first segment in the IPv6 Segment Routing Header NEXT Signals completion of active segment and activation of the next segment in the segment list POPping of the top label in the label stack Activation of the next segment in the IPv6 Segment Routing Header segment list CONTINUE Signals that the currently active segment is not yet complete and needs to remain active SWAP of the top label Standard IPv6 forwarding based on destination address 50

51 MPLS data plane 51

52 MPLS data plane A segment is encoded as an MPLS label An ordered list of segments is encoded as a stack of labels The active segment is the one on the top of the label stack i.e. top MPLS label There is zero change to the operation of the standard MPLS data plane 52

53 SR Global Block (SRGB) Set of local MPLS labels reserved for global segments. Network operation is greatly simplified if all nodes in the SR domain are configured with the same SRGB. In this example, SRGB range is SRGB MPLS Label Space 53

54 Label advertisement with common SRGB Segment Identifiers: Node-SIDs Allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 54

55 SID advertisements (1) Association of SID to prefix advertised by IGP SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: P1 P2 P3 ILM In-label Out-label Interface To-P2 ILM (no-php) In-label Out-label Interface To-P3 ILM (with PHP) In-label Out-label Interface To-P3 ILM In-label Out-label Interface Local Identical SRGB on all nodes 55

56 SID advertisements (2) Association of SID to prefix advertised by IGP SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: P1 P2 P3 ILM (no-php) In-label Out-label Interface To-P2 ILM (with PHP) In-label Out-label Interface To-P2 ILM In-label Out-label Interface Local ILM (no-php) In-label Out-label Interface To-P2 ILM (with PHP) In-label Out-label Interface To-P2 Identical SRGB on all nodes 56

57 SID advertisements (3) Association of SID to prefix advertised by IGP SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: P1 P2 P3 ILM In-label Out-label Interface Local ILM (no-php) In-label Out-label Interface To-P1 ILM (with PHP) In-label Out-label Interface To-P1 ILM In-label Out-label Interface To-P2 Identical SRGB on all nodes 57

58 Dealing with different SRGBs If nodes in the same SR domain have different SRGBs, absolute label values can not be used In such a case, a globally unique index is used instead. The local label at a given node is found by adding the globally-unique index to the node s SRGB SRGB MPLS Label Space Index used as offset 58

59 Using index values Example: index value of Node A Node B SRGB SRGB MPLS Label Space 0 MPLS Label Space Absolute label value = = Absolute label value = =

60 Label index advertisement with SRGB Segment Identifiers: Node-SIDs Allocated as globally-unique index values SRGB: Different SRGB configured on all nodes 60

61 SID advertisements (1) Association of SID to prefix advertised by IGP Label index: 1 SRGB: Label index: 2 SRGB: Label index: 3 SRGB: P1 P2 P3 ILM In-label Out-label Interface To-P2 ILM (no-php) In-label Out-label Interface To-P3 ILM (with PHP) In-label Out-label Interface To-P3 ILM In-label Out-label Interface Local Identical SRGB on all nodes 61

62 SID advertisements (2) Association of SID to prefix advertised by IGP Label index: 1 SRGB: Label index: 2 SRGB: Label index: 3 SRGB: P1 P2 P3 ILM (no-php) In-label Out-label Interface To-P2 ILM (with PHP) In-label Out-label Interface To-P2 ILM In-label Out-label Interface Local ILM (no-php) In-label Out-label Interface To-P2 ILM (with PHP) In-label Out-label Interface To-P2 Identical SRGB on all nodes 62

63 SID advertisements (3) Association of SID to prefix advertised by IGP Label index: 1 SRGB: Label index: 2 SRGB: Label index: 3 SRGB: P1 P2 P3 ILM In-label Out-label Interface Local ILM (no-php) In-label Out-label Interface To-P1 ILM (with PHP) In-label Out-label Interface To-P1 ILM In-label Out-label Interface To-P2 Identical SRGB on all nodes 63

64 BGP/MPLS VPN (common to all subsequent use cases) Routing: BGP/MPLS VPN label advertisement 64

65 Example: service label exchange All subsequent examples use the service label value of P1 P2 P3 CE1 BGP-MPLS PE1 FEC: VPN-X PE2 CE2 Label: P4 P5 Metric: 100 P All IGP metrics are equal to 10 unless otherwise indicated 65

66 Use case 1: ECMP-aware shortest path routing Routing: ECMP-aware shortest path routing Segment Identifiers: Node-SIDs only Allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 66

67 Objectives Objectives: SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: Deliver traffic between PE1 and PE2 via the shortest IGP path P1 P2 P3 CE1 PE1 PE2 CE SID: 111 SRGB: SID: 222 SRGB: Use case 1 P4 P5 Metric: 100 P6 Routing SIDs Shortest-path Node SID: 104 SRGB: SID: 105 SRGB: SID: 106 SRGB: Label Value SRGB Absolute Common 67

68 Building the ILM ILM ILM Outlabel Inlabel Outlabel Intf To-P SID: 101 SRGB: ILM Inlabel Intf To-P SID: 102 SRGB: SID: 103 SRGB: ILM In-label Out-label Interface To-PE2 Inlabel Outlabel Intf To-P1 P1 P2 P3 CE1 ILM PE1 PE2 CE2 Inlabel Outlabel Intf SID: 111 SRGB: To-PE SID: 222 SRGB: Routing SIDs Label Value SRGB Use case 1 Shortest-path Node Absolute Common ILM P SID: 104 SRGB: Inlabel Outlabel Intf ILM P SID: 105 SRGB: Inlabel Outlabel Intf Metric: 100 P SID: 106 SRGB: Association of SID to prefix advertised by IGP All IGP metrics are equal to 10 unless otherwise indicated To-P To-P2 Identical SRGB on all nodes 68

69 Traffic forwarding Swap 222 for SID: 101 P Swap 222 for SID: 102 P Swap 222 for SID: 103 P CE1 PE1 PUSH 1234, POP 222, PE2 CE SID: SID: 222 Use case 1 P4 P5 Metric: 100 P6 Routing SIDs Shortest-path Node SID: SID: SID: 106 Label Value SRGB Absolute Common All IGP metrics are equal to 10 unless otherwise indicated 69

70 Use case 2: ECMP-aware shortest path routing Routing: ECMP-aware shortest path routing Segment Identifiers: Node-SIDs only Allocated as index values SRGB: Different SRGB configured on different nodes 70

71 Objectives Objectives: SID index: 1 SRGB: SID index: 2 SRGB: SID index: 3 SRGB: Deliver traffic between PE1 and PE2 via the shortest IGP path P1 P2 P3 CE1 PE1 PE2 CE SID index: 11 SRGB: Use case 2 P4 P5 Metric: 100 P6 Routing SIDs Shortest-path Node SID index: 4 SRGB: SID index: 5 SRGB: SID index: 6 SRGB: Label Value SRGB Index Different All IGP metrics are equal to 10 unless otherwise indicated 71

72 Building the ILM ILM ILM Outlabel Inlabel Outlabel Intf To-P SID index: 1 SRGB: ILM Inlabel Intf To-P SID index: 2 SRGB: SID index: 3 SRGB: ILM In-label Out-label Interface To-PE2 Inlabel Outlabel Intf To-P1 P1 P2 P3 CE1 ILM PE1 PE2 CE2 Inlabel Outlabel Intf SID index: 11 SRGB: To-PE SID index: 22 SRGB: Routing SIDs Label Value SRGB Use case 2 Shortest-path Node Index Different ILM P SID index: 4 SRGB: Inlabel Outlabel Intf ILM P SID index: 5 SRGB: Inlabel Outlabel Intf Metric: 100 P SID index: 6 SRGB: Association of SID to prefix advertised by IGP All IGP metrics are equal to 10 unless otherwise indicated To-P To-P2 72

73 Traffic forwarding Swap 222 for SID index: 1 P Swap 322 for SID index: 2 P Swap 422 for SID index: 3 P CE1 PE1 PUSH 1234, POP 822, PE2 CE SID index: SID index: 22 Use case 2 P4 P5 Metric: 100 P6 Routing SIDs Shortest-path Node SID index: SID index: SID index: 6 Label Value SRGB Index Different All IGP metrics are equal to 10 unless otherwise indicated 73

74 Routing: Traffic-engineered Use case 3: SR-TE Segment Identifiers: Node-SIDs only Allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 74

75 Objectives Objectives: SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: All traffic from PE1 to PE2 should traverse P2 but avoid the P2- P3 link P1 P2 P3 CE1 PE1 PE2 CE SID: 111 SRGB: SID: 222 SRGB: Use case 3 P4 P5 P6 Routing SIDs Traffic-engineered Node SID: 104 SRGB: SID: 105 SRGB: SID: 106 SRGB: Label Value SRGB Absolute Common All IGP metrics are equal to 10 unless otherwise indicated 75

76 Building the ILM ILM Outlabel Inlabel Outlabel Intf To-P SID: 101 SRGB: ILM Inlabel Intf To-P SID: 102 SRGB: SID: 103 SRGB: ILM In-label Out-label Interface To-PE To-P To-P To-P Local P1 P2 P To-P To-P To-PE2 Routing SIDs Label Value SRGB CE1 Use case SID: 111 SRGB: Traffic-engineered Node Absolute Common P SID: 104 SRGB: ILM P5 ILM Inlabel Outlabel PE1 Association of Inlabelabel Out- SID to prefix Intf PE2 CE2 advertised by IGP SID: 105 SRGB: Intf To-P To-PE2 P SID: 106 SRGB: SID: 222 SRGB: Association of SID to prefix advertised by IGP All IGP metrics are equal to 10 unless otherwise indicated 76

77 Traffic forwarding CE1 Use case SID: 111 Swap for Pop SID: 101 P1 PUSH 1234, 222, 105, 102 PE PE2 CE2 P Pop SID: 102 P2 P SID: 103 P3 222 P6 Swap 222 for 222 POP 222, SID: 222 Routing SIDs Traffic-engineered Node SID: SID: SID: 106 Label Value SRGB Absolute Common All IGP metrics are equal to 10 unless otherwise indicated 77

78 Routing: Traffic-engineered. Difference from use case 3 is the link-metric of 100 from PE5 to PE6. How do we force traffic over this link? Use case 4: SR-TE Segment Identifiers: Node-SIDs and Adj-SIDs Node-SIDs allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 78

79 Objectives Objectives: SID: 101 SRGB: SID: 102 SRGB: SID: 103 SRGB: All traffic from PE1 to PE2 should traverse P2 but avoid the P2- P3 link P1 P2 P3 CE1 PE1 PE2 CE SID: 111 SRGB: Use case 4 P4 P5 Metric: 100 P6 Routing SIDs Traffic-engineered Node, Adjacency SID: 104 SRGB: SID: 105 SRGB: SID: 106 SRGB: Label Value SRGB Absolute Common All IGP metrics are equal to 10 unless otherwise indicated 79

80 Building the ILM ILM Outlabel Inlabel Outlabel Intf To-P SID: 101 SRGB: ILM Inlabel Intf To-P SID: 102 SRGB: SID: 103 SRGB: ILM In-label Out-label Interface To-PE To-P To-P To-P Local P1 P2 P To-P To-P To-PE2 Routing SIDs Label Value SRGB CE1 Use case SID: 111 SRGB: Traffic-engineered Node, Adjacency Absolute Common P SID: 104 SRGB: ILM P5 ILM Outlabel PE1 Association of Inlabelabel Out- SID to prefix Intf PE2 CE2 advertised by IGP SID: 105 SRGB: Inlabel To-PE2 Metric: 100 Intf To-P To-P To-P6 P SID: 106 SRGB: SID: 222 SRGB: Association of SID to prefix advertised by IGP All IGP metrics are equal to 10 unless otherwise indicated 80

81 Traffic forwarding Routing SIDs Label Value SRGB CE1 Use case 4 Swap for Pop SID: 101 SID: SID: 111 Traffic-engineered Node, Adjacency Absolute Common P1 PUSH 1234, 222, 1001, 105, 102 PE PE2 CE2 P SID: Pop 105, 1001 P2 P SID: Metric: SID: 103 P3 222 P SID: 106 Swap 222 for 222 POP 222, SID: 222 All IGP metrics are equal to 10 unless otherwise indicated 81

82 Routing: Traffic-engineered Use case 5: SR-TE Segment Identifiers: Node-SIDs and Anycast-SIDs Allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 82

83 Anycast segments Anycast-SID allows ECMPaware shortest-path forwarding to the closest node of the anycast set A1 Anycast Group A SID: 100 A3 All routers in the anycast set advertise the same anycast prefix with the same SID value SID: 111 SRGB: R1 R SID: 113 SRGB: PE1 A2 A4 PE3 PE2 B1 B3 PE SID: 112 SRGB: R2 R SID: 114 SRGB: Use case 5 Routing Traffic-engineered SIDs Node, Anycast Label Value Absolute SRGB Common B2 Anycast Group B SID: 200 B4 All IGP metrics are equal to 10 unless otherwise indicated Identical SRGB on all nodes 83

84 Objectives Objectives: A1 Anycast Group A SID: 100 A3 All traffic from PE1 to PE3 should traverse the top plane SID: 111 SRGB: R1 R SID: 113 SRGB: PE1 A2 A4 PE3 PE2 B1 B3 PE SID: 112 SRGB: R2 R SID: 114 SRGB: Use case 5 Routing Traffic-engineered SIDs Node, Anycast Label Value Absolute SRGB Common B2 Anycast Group B SID: 200 B4 All IGP metrics are equal to 10 unless otherwise indicated Identical SRGB on all nodes 84

85 Traffic forwarding Swap 100 for Pop 100 A A3 Swap 113 for Swap 113 for 113 PE1 forces packets destined for PE3 to go via Anycast Group A SID: 111 SRGB: R1 R SID: 113 SRGB: PUSH 1234, 113, 100 PE1 A2 A4 PE3 POP 113, 1234 PE2 B1 B3 PE SID: 112 SRGB: R2 R SID: 114 SRGB: Use case 5 B2 B4 Routing Traffic-engineered SIDs Label Value Node, Anycast Absolute Anycast Group B SID: 200 All IGP metrics are equal to 10 unless otherwise indicated SRGB Common Identical SRGB on all nodes 85

86 IPv6 data plane 86

87 IPv6 data plane Requires a new type of Routing Header A segment is encoded as an IPv6 address (prefix-sid is the prefix itself). SRv6 Segment (abbreviated as SRv6-SID) is an 128-bit value An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header The active segment is indicated by the Destination Address (DA) of the packet. The DA of the packet changes at each segment completion. The final DA of the packet is encoded as the last segment of the path The next active segment is indicated by a pointer in the new routing header 87

88 Segment Routing Header (SRH) 32 bits next header hdr ext len routing type segments left last entry flags tag segment list[0] (128 bits IPv6 address) next header: - Header immediately following the SRH segments left: - index of the next segment to inspect last entry: - index of last element of the segment list segment list[n] (128 bits IPv6 address) optional TLVs flags: - P: protected, set when packet has been rerouted through an FRR mechanism - O: set for OAM packets - A: alert for presence of TLV objects - H: HMAC is present if set 88

89 Segment Routing Header (SRH) The SRH is added to the packet at its source, either: At the node originating the packet (host, server) At the ingress mode of an SR domain where the ingress node receives an IPv6 packet and encapsulates it into an outer IPv6 header followed by a Segment Routing Header The source address of the packet is the ingress node The destination address is set as the first segment of the path The last segment of the path is the egress node of the SR domain 89

90 Creating the SRH The source SR node does the following: Set SA = address of source SR node/sr-domain ingress node Set DA = value of the first segment Set first element of segment list = last segment Set second element of segment list = penultimate segment <and so on segment list is encoded in the reverse order of the path> Set Segments Left = n-1 where n = number of elements in the Segment List Set Last Entry field = n-1 where n = number of elements in the Segment List 90

91 Handling the SRH At each segment of the SRH, the following operations take place: IF SegmentsLeft > 0 THEN decrement SL update the IPv6 DA with SRH[SL] FIB lookup on updated DA forward according to the matched entry ELSE drop the packet 91

92 BGP Egress Peer Engineering (EPE) 92

93 BGP Egress Peer Engineering Problem statement (RFC7855): A centralised controller should be able to instruct an ingress PE router or a content source within the domain to use a specific egress PE and a specific interface/neighbor to reach a particular destination 93

94 SR BGP-EPE Segment Routing enables a centralised (SDN) controller to program any egress peer selection policy at ingress border routers or at hosts within the domain: Solution is called BGP Egress Peer Engineering (BGP-EPE) Centralised controller is called the BGP-EPE controller Egress border router where the BGP-EPE traffic steering functionality is implemented is called a BGP-EPE-enabled border router The policy programmed at an ingress border router is called a BGP- EPE policy 94

95 BGP peering segments An ingress border router of an AS can steer a flow along a selected AS, towards a selected egress border router of the AS and through a specific peer by using BGP Egress Peer Engineering capabilities BGP Peering Segments Segments identifying by a BGP EPE (Egress Peer Engineering)-enabled node. Enable the expression of source-routed interdomain paths Peer Node Segments Local (PeerNode-SID) Segment representing a BGP peering node Semantics: SR header operation: NEXT Next-hop: connected peering node to which the segment is related Peer Adjacency Segments Local (PeerAdj-SID) Segment representing an adjacency to a BGP peering node Semantics: SR header operation: NEXT Next-hop: peer connected through the interface to which the segment is related Peer Set Segments Local (PeerSet-SID) Segment representing a set of BGP peering nodes Semantics: SR header operation: NEXT Next-hop: load-balance across any connected interface to any peer in the related group 95

96 Routing: Traffic-engineered Use case: BGP-EPE Segment Identifiers: BGP-Peering segments SRGB: Identical SRGB configured on all nodes 96

97 BGP-EPE network BGP EPE Controller Node- SID: 32 B D G A Node- SID: 16 AS1 Node- SID: 64 C E AS2 AS4 L/8 K/8 AS3 K F 97

98 BGP-EPE Segments BGP-LS NLRIs corresponding to the BGP-EPE segments BGP EPE Controller Node- SID: 32 B D G A Node- SID: 16 AS1 Node- SID: 64 C E AS2 AS4 L/8 K/8 F AS3 K C s ILM In Label Op Out intf 1012 Pop Link to D 1022 Pop Link to E 1032 Pop Upper link to F BGP Peering segments allocated by PE C Peer Node Segments D 1012 E 1022 F 1052 Peer Adj Segments Upper link to F 1032 Lower link to F 1042 Peer Set Segments E, F Pop Lower link to F 1052 Pop Load balance on any link to F 1060 Pop Load balance on any link to E or F 98

99 BGP-LS advertisements BGP-LS NLRIs corresponding to the BGP-EPE segments BGP EPE Controller Peer Node SID to D Descriptors: Node: BGP-router-ID(C), AS1 Peer: BGP-router-ID(D), AS2 Link: IP address of C s link to D, IP address of D s link to C Attributes: PeerNode SID: 1012 C s ILM In Label Op Out intf 1012 Pop Link to D 1022 Pop Link to E 1032 Pop Upper link to F BGP Peering segments allocated by PE C Peer Node Segments D 1012 E 1022 F 1052 Peer Adj Segments Upper link to F 1032 Lower link to F 1042 Peer Set Segments E, F Pop Lower link to F 1052 Pop Load balance on any link to F 1060 Pop Load balance on any link to E or F 99

100 SR BGP-EPE input policy The BGP-EPE policy can be usually expressed at the ingress border router via a two-entry segment list where: The first elements is the IGP prefix SID of the selected egress border router AND The second element is a BGP Peering SID at the selected egress border router Note that BGP-EPE functionality is only required on the BGP-EPE-enabled egress border router; the ingress border router simply needs to support SR-TE 100

101 Input policy programming Input policy configured with SR-TE tunnel +steering policy via PCE-P/Netconf BGP EPE Controller Node- SID: 32 B D G A Node- SID: 16 AS1 Node- SID: 64 C E F AS2 AS3 Example input policy: route all traffic to L/8 via egress border router C s lower link to peer F SR-TE tunnel TE1: push {1042, 64} ip route L/8 next-hop TE1 K AS4 C s ILM In Label Op L/8 K/8 Out intf 1012 Pop Link to D 1022 Pop Link to E 1032 Pop Upper link to F 1042 Pop Lower link to F 1052 Pop Load balance on any link to F 1060 Pop Load balance on any link to E or F 101

102 Traffic flow BGP EPE Controller PUSH 1042, Node- SID: 32 B D AS2 G L/8 A Node- SID: 16 AS1 Node- SID: 64 C E AS4 K/8 Pop 64, 1042 F AS3 K 102

103 Interworking with LDP 103

104 Distributing SR labels in LDP A node that has both Segment Routing and LDP capability and active LDP neighbors is required to: create LDP bindings for each Prefix-SID and Node-SID learned in the SR domain Stitch the incoming LDP label to the outgoing SR label 104

105 Segment Routing Mapping Server (1) Segment Routing Mapping Server (SRMS): SR-capable router that advertises mappings between prefixes and labels for prefixes that it does now own itself. That is, the SRMS advertises prefix-to-sid mappings on behalf of non-sr-capable routers. Control-plane function only; the SRMS is not in the data path and can be located anywhere Multiple SRMSs can be used for redundancy Requires the use of SR IGP extensions 105

106 Segment Routing Mapping Server (2) A node that has both Segment Routing and LDP capability and active LDP neighbors is required to: create LDP bindings for each Prefix-SID and Node-SID learned in the SR domain Stitch the incoming SR label to the outgoing LDP label 106

107 Routing: Traffic-engineered Use case: SR-TE Segment Identifiers: Node-SIDs Allocated as absolute globallysignificant MPLS label values SRGB: Identical SRGB configured on all nodes 107

108 Mixed-LDP/SR network SID: 102 SRGB: PE2 PE4 SR-only PE1 P5 P6 P7 P8 PE3 SR & LDP SID: 101 SRGB: SID: 105 SRGB: SID: 106 SRGB: LDP-only SR domain LDP domain Requirement: Contiguous MPLS tunnels must be built: from PE1 to PE3 from PE3 to PE1 108

109 LDP to SR direction: label distribution ILM SID: 102 SRGB: In-label Out-Label Intf To-P7 Association of SID to prefix advertised by IGP PE2 LDP FECs advertised PE4 PE1 P5 P6 P7 P8 PE3 SID: 101 SRGB: SID: 105 SRGB: SID: 106 SRGB: LDP FECs advertised SR-only SR domain LDP domain SR & LDP LDP labels allocated by P7 ILM LDP-only P7 creates LDP bindings for all SR Prefix-SIDs and Node-SIDs FEC Label PE1 701 PE2 702 P5 705 In-label Out-Label Intf To-P To-P To-P6 P To-P6 109

110 LDP to SR direction: traffic flow SID: 102 SRGB: PE2 Swap 101 for 101 Swap 101 for Swap 701 for 101 Swap 801 for 701 PE4 PUSH 1234, 801 POP 101, 1234 PE1 P5 P6 P7 P8 PE3 SID: 101 SRGB: SID: 105 SRGB: SID: 106 SRGB: SR-only SR domain LDP domain SR & LDP LDP-only 110

111 SR to LDP direction: label distribution ILM ILM SID: 102 SRGB: In-label Out-Label Intf To-P7 In-label Out-Label Intf To-PE3 PE2 Configured as SR Mapping Server (SRMS) PE4 PE1 P5 P6 P7 P8 PE3 SID: 101 SRGB: SID: 105 SRGB: SID: 106 SRGB: LDP FEC: PE3 Label: 803 LDP FEC: PE3 Label: 303 SR-only SR domain LDP domain SR & LDP Local policy is configured on P5 to advertise SIDs for LDP-only nodes SIDs advertised by P5 FEC Label P8 108 PE3 103 PE4 104 ILM In-label Out-Label Intf To-P8 LDP-only 111

112 SR to LDP direction: traffic flow SID: 102 SRGB: PE2 Swap 103 for 103 Swap 103 for Swap 103 for 803 Swap 803 for 303 PE4 POP 803, 1234 PUSH 1234, 103 PE1 P5 P6 P7 P8 PE3 SID: 101 SRGB: SID: 105 SRGB: SID: 106 SRGB: SR-only SR domain LDP domain SR & LDP LDP-only 112

113 IGP extensions 113

114 OSPFv2: SR capabilities An OSPFv2 router s SR capabilities are advertised in the Router Information Opaque LSA (RFC7770) SR-Algorithm TLV Used within the Router Information Opaque LSA to advertise the supported algorithms type 32 bits Algorithm 1 Algorithm Algorithm n algorithm: - 0: SPF - 1: Strict SPF length SID/Label Range TLV Used within the Router Information Opaque LSA to advertise the SRGB type range size 32 bits Sub-TLVs (variable) length reserved range size: size of SRGB sub-tlv: SID/Label sub-tlv indicating first SID/Label in the range SID/Label Sub-TLV Used to advertise the SID or label value type 32 bits SID/Label length 114

115 OSPFv2: Extended Prefix Opaque LSA Extended Prefix Opaque LSA used to advertise additional prefix attributes beyond what is possible with the fixed-format LSAs defined in RFC2328. LS age Options LS type opaque type opaque ID Advertising router LS sequence number LS checksum length TLVs Opaque type: - 7 (OSPFv2 Extended Prefix Opaque LSA) LS Type: - 10: area-local scope - 11: AS-wide scope TLV: - E.g. OSPF2 Extended Prefix TLV 115

116 OSPFv2: Extended Prefix TLV Extended Prefix TLV TLV of the OSPF Extended Prefix Opaque LSA (RFC7684) Used to advertise various additional attributes of the prefix 32 bits type length route type Prefix Length AF flags address prefix (variable) sub-tlvs (variable) route type: - 1: intra-area - 2: inter-area - 5: AS-external - 7: NSSA-external AF: - Address-family: only 1Pv4 unicast is supported algorithm: - 0: SPF - 1: Strict SPF sub-tlvs: - E.g. OSPF2 Prefix-SID sub-tlv 116

117 OSPFv2: Prefix SID sub-tlv Prefix-SID sub-tlv Sub-TLV of the OSPF Extended Prefix TLV (RFC7684) Flags NP M E V L 32 bits type length flags reserved MT-ID algorithm SID/Index/Label (variable) flags: - NP: No-PHP - M: Mapping Server - E-Flag: Explicit-Null - V: if set, SID is an absolute value - L: set for local significance MT: - Multi-Topology ID algorithm: - 0: SPF - 1: Strict SPF 117

118 OSPFv2: Extended Prefix Range TLV Extended Prefix Range TLV TLV of the OSPF Extended Prefix Opaque LSA (RFC7684) Used to advertise prefixes to SID/Label mappings as part of Segment Routing Mapping Server (SRMS) function 32 bits type length Prefix Length AF range size flags reserved address prefix (variable) sub-tlvs (variable) flags: - IA: set for inter-area type Range size: - Size of advertised range sub-tlvs: - e.g. Prefix-SID sub-tlv signifying start of the SID range Flags IA 118

119 OSPFv2: Extended Link Opaque LSA Extended Link Opaque LSA used to advertise additional link attributes beyond what is possible with the fixed-format LSAs defined in RFC bits LS age Options LS type opaque type opaque ID Advertising router LS sequence number LS checksum length TLVs Opaque type: - 8 (OSPFv2 Extended Link Opaque LSA) LS Type: - 10: area-local scope - 11: AS-wide scope TLV: - E.g. OSPF2 Extended Link TLV 119

120 OSPFv2: Extended Link TLV Extended Link TLV TLV of the OSPF Extended Link Opaque LSA (RFC7684) Used to advertise various additional attributes of the link 32 bits type length link type reserved link ID link data sub-tlvs (variable) link type, link ID, link data: - Identical to LSA type-1 values sub-tlvs: - E.g. OSPF2 Prefix-SID sub-tlv 120

121 OSPFv2: Adjacency SID sub-tlv Adjacency-SID sub-tlv Sub-TLV of the OSPF Extended Link TLV (RFC7684) Flags 32 bits type length flags reserved MT-ID weight SID/Index/Label (variable) B V L G P flags: - B: Adjacency is eligible for protection - V: if set, SID is an absolute value - L: set for local significance - G: refers to a group of adjacencies - P: Adj-SID is persistently allocated MT: - Multi-Topology ID weight: - used for load-balancing purposes 121

122 ISIS: SR capabilities An ISIS router s SR capabilities are advertised in the IS-IS Router Capability TLV-242 SR-Algorithm sub-tlv Used to advertise the supported algorithms SR-capabilities sub-tlv Used to advertise the SRGB 32 bits 32 bits type length Algorithm 1 Algorithm 2 Algorithm Algorithm n type length range flags SID/Label Sub-TLV algorithm: - 0: SPF - 1: Strict SPF range size: size of SRGB sub-tlv: SID/Label sub-tlv indicating first SID/Label in the range type SID/Label Sub-TLV Used to advertise the SID or label value 32 bits length SID/Label 122

123 IS-IS: Prefix SID sub-tlv Prefix-SID sub-tlv Carries an IGP-Prefix-SID Can be present in TLV-135,235,236,237,Binding- TLV Flags R N P E V L 32 bits type length flags algorithm SID/Index/Label (variable) flags: - R: Re-advertisement flag, prefix has been propagated from another level - N: set for Node-SID - P: no PHP if set - E-Flag: Explicit-Null - V: if set, SID is an absolute value - L: set for local significance algorithm: - 0: SPF - 1: Strict SPF TLV-135 (Extended IPv4 reachability) defined in [RFC5305 ]. TLV-235 (Multitopology IPv4 Reachability) defined in [RFC5120 ]. TLV-236 (IPv6 IP Reachability) defined in [RFC5308 ]. TLV-237 (Multitopology IPv6 IP Reachability) defined in [RFC5120 ]. 123

124 IS-IS: SID/Label Binding TLV Prefix-SID sub-tlv Used to advertise prefixes to SID/Label mappings as part of Segment Routing Mapping Server (SRMS) function Flags F M S D A 32 bits type length flags reserved range prefix length prefix prefix (continued, variable) sub-tlvs(variable) flags: - F: if set, IPv6 encap. Else, IPv4 - M: set for a mirrored context - S: set to allow flooding across entire domain - D: set when TLV is leaked from L2 to L1 - A: attached flag range: - allows advertising a range of prefixes and their labels sub-tlvs: - e.g. Prefix-SID sub-tlv signifying start of the SID range 124

125 IS-IS: Adjacency SID sub-tlv Adjacency-SID sub-tlv Carries an IGP-Adj-SID Can be present in TLV-22, 23, 222, 223, 141 Flags F B V L S P 32 bits type length flags weight SID/Index/Label (variable) flags: - F: if set, IPv6 encap. Else, IPv4 - B: Adjacency is eligible for protection - V: if set, SID is an absolute value - L: set for local significance - S: refers to a set of adjacencies - P: Adj-SID is persistently allocated weight: - used for load-balancing purposes TLV-22 (Extended IS reachability)[rfc5305] TLV-222 (Multitopology IS)[RFC5120] TLV-23 (IS Neighbor Attribute)[RFC5311] TLV-223 (Multitopology IS Neighbor Attribute)[RFC5311] TLV-141 (inter-as reachability information)[rfc5316] 125

126 References 126

127 References RFC Source Packet Routing in Networking (SPRING) Problem Statement and Requirements draft-ietf-spring-segment-routing-12 draft-ietf-spring-segment-routing-mpls-10 draft-ietf-spring-segment-routing-central-epe-06 draft-ietf-6man-segment-routing-header-06 draft-ietf-ospf-segment-routing-extensions-17 draft-ietf-isis-segment-routing-extensions-13 draft-ietf-spring-segment-routing-ldp-interop

128 Thank You! End of session WSDN01_v0.1 Issue Date: [Date] Revision: [xx]