Enrique Dávila
LACNOG 16 – San José, Costa RicaSegment Routing
Services Technical Leader
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• Technology Overview
• Use Cases
• Control and Data Plane
• Traffic Protection
• Conclusions
Agenda
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• 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 without any further
per-flow state
• Segment: an identifier for any type of instruction• forwarding or service
Segment Routing
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• 16000 + Index
• Signaled by ISIS/OSPF
IGP Prefix Segment
10
11
• Shortest-path to the IGP prefix
• Global12
13
14
DC (BGP-SR)
2 4
6 5
7
WAN (IGP-SR)
3
1
PEER
16005
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• 1XY• X is the “from”• Y is the “to”
• Signaled by ISIS/OSPF
IGP Adjacency Segment
10
11
• Forward on the IGP adjacency
• Local12
13
14
DC (BGP-SR)
2 4
6 5
7
WAN (IGP-SR)
3
1
PEER
124
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• Shortest-path to the BGP prefix
• Global
• 16000 + Index
• Signaled by BGP
BGP Prefix Segment
10
11
12
13
14
DC (BGP-SR)
2 4
6 5
7
WAN (IGP-SR)
3
1
PEER
16001
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• Forward to the BGP peer
• Local
• 1XY• X is the “from”• Y is the “to”
• Signaled by BGP-LS (topology information) to the controller
BGP Peering Segment
10
11
12
13
14
DC (BGP-SR)
2
6
7
WAN (IGP-SR)
3
1
PEER
LowLat, LowBW
4
5High Lat, High BW
147
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• WAE collects via BGP-LS• IGP segments• BGP segments• Topology
WAN Controller
10
11
12
13
14
DC (BGP-SR)
2 4
6 5
7
WAN (IGP-SR)
3
1
PEER
Low Lat, Low BW
BGP-LS
BGP-LS
BGP-LS
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• 16001• 16002• 124• 147
• WAE programs a single per-flow state to create an application-engineered end-to-end policy
An end-to-end path as a list of segments
10
11
13
14
DC (BGP-SR)
2 4
6 5
7
3
1
PEER
Low Lat, Low BW
50
Default ISIS cost metric: 10
WAN (IGP-SR)
12{16001,
16002,124,147}
PCEP, Netconf, BGP
• WAE computes that the green path can be encoded as
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Segment Routing StandardizationSample IETF Documents
Segment Routing Architecture (draft-ietf-spring-segment-routing)
Problem Statement and Requirements (draft-ietf-spring-problem-statement)
IPv6 SPRING Use Cases (draft-ietf-spring-ipv6-use-cases)
Segment Routing Use Cases(draft-filsfils-spring-segment-routing-use-cases)
Topology Independent Fast Reroute using Segment Routing(draft-francois-spring-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)
• IETF standardization in SPRING
• working group
• Protocol extensions progressing in multiple groups• IS-IS• OSPF• PCE• IDR• 6MAN
• Broad vendor and customer support• Close to 30 IETF drafts in progress
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Use Cases
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• IGPonly• No LDP, no RSVP-TE
• ECMP
IPv4/6 VPN/Service transport
1
2 3
4
6 5
7
Site1 Site216007vpnpkt
16007vpnpkt
pkt
pktvpn
pkt
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• Seamless deployment
Seamless interworking with LDP
1
2 3
4
6 5
7
Site1 Site2
pkt
pktvpn
pkt
16007vpnpkt
16007vpnpkt
pktvpn
LDP(7)
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• 50msec FRR in any topology
• IGP Automated• No LDP, no RSVP-TE
• Optimum• Post-convergence path
• No midpoint backup state
• Detailed operator report• S. Litkowski, B. Decraene,Orange
• Mate Design• How many backup segments• Capacity analysis
Topology-Independent LFA (TI-LFA FRR)
1
2 3
4
6 5
7
1600516007
pkt
pkt16007
pkt16007
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• 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
Automated Traffic Matrix Collection1 2 3 4
1
2
3
4
1
2
4
3
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• 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 engineeringegress traffic from DC to peer• BGP Prefix and Peering Segments
Optimized Content Delivery
1 2
6
4 3AS1
5
7
AS6AS5
AS7
1600316002
126pkt
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• Per-application flow engineering
• End-to-End• DC, WAN, AGG, PEER
• Millions of flows• No signaling• No midpoint state• No reclassification at
boundaries
Application Engineered Routing
10
11
13
14
DC (or AGG)
12Push{16001,
200, 147}
Low-Latency to 7for application A12
2 4
6 5
7
ISIS:35
Default ISIS cost metric: 10Default Latency metric: 10
WAN
3
1
BSID:200
200: popand push{16002,16004}
PEER
Low Lat, Low BW
Low-Lat to4
PeerSID: 147, Low Lat, Low BW
PeerSID: 147, High Lat, High BW
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flow engineering
• End-to-End• DC, WAN, AGG, PEER
• Millions of flows• No signaling• No midpoint state• No reclassification at
boundaries
Application Engineered Routing
10
11
13
14
DC (or AGG)
12Push{16010,
16001,200, 147}
Low-Latency to 7, DC Plane 0 only, for application A12
• Per-application
2 4
6 5
7
ISIS:35
Default ISIS cost metric: 10Default Latency metric: 10
WAN
3
1
BSID:200
200: popand push{16002,16004}
PEER
Low Lat, Low BW
Low-Lat to4
PeerSID: 147, Low Lat, Low BW
PeerSID: 147, High Lat, High BW
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A Closer look to Control and Data Plane
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MPLS Control and Forwarding Operation with Segment Routing
PE1 PE2
IGP PE2
Services
IPv4 IPv6 IPv4 VPN
IPv6 VPN VPWS VPLS
Packet Transport
PE1
LDP RSVP BGP Static
MPLS Forwarding
IS-IS OSPF
No changes to control or forwarding plane
IGP label distribution for IPv4 and IPv6, same forwarding plane
BGP /LDP
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• Prefix SID• SID encoded as an index• Index represents an offset from SRGBbase• Index globally unique• SRGB may vary across LSRs• SRGB (base and range) advertised with
router capabilities
• AdjacencySID• SID encoded as absolute (i.e. not indexed)
value• Locally significant• Automatically allocated for each adjacency
SID Encoding
SRGB = [ 16000 - 23999 ]. Advertised as base = 16,000, range = 7,999Prefix SID = 16041. Advertised as Prefix SID Index =41Adjacency SID = 24000. Advertised as Adjacency SID = 24000
SR-enabled Node
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Payload
MPLS Data Plane Operation (Prefix SID)SRGB [16,000 – 23,999 ]
Loopback X.X.X.X Prefix SID Index = 41
SRGB [16,000 – 23,999 ]A
SRGB [16,000 – 23,999 ]B
SRGB [26,000 – 23,999 ]C D
Payload
16041
VPN Label
Push Push
Swap Pop
Payload Payload
26041
VPN Label
Payload
VPN Label
Pop
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MPLS Data Plane Operation (Adjacency SIDs)
Payload Payload
PushPushPush
Pop Pop
Payload Payload
VPN Label
24000VPN Label
Pop
SID = 24000SID = 24000SID = 24010
24000
24000
VPN Label
Payload
MPLS Label Range [ 24000– 265535 ]
A
Adjacency
MPLS Label Range [ 24000– 265535 ] B
Adjacency
MPLS Label Range [ 24000– 265535 ]
CAdjacency
MPLS Label Range [ 24000– 265535 ]
D
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• LFIB populated by IGP (ISIS /OSPF)
• Forwarding table remains constant (Nodes + Adjacencies) regardless of number of paths
• Other protocols (LDP, RSVP, BGP) can still program LFIB
MPLS LFIB with Segment Routing
PE
PE
PE
PE
PE
PE
PE
PE
P
In Label
Out Label
Out Interface
L1 L1 Intf1L2 L2 Intf1… … …L8 L8 Intf4L9 L9 Intf2L10 Pop Intf2… … …Ln Pop Intf5
Network Node Segment Ids
Node Adjacency Segment Ids
Forwarding table remains constant
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Traffic Protection
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• 100%-coverage 50-msec link and node 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 traffic
Topology Independent LFA (TI-LFA) – Benefits
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• Leverages existing and proven LFA technology• P space: set of nodes reachable from node S (PLR) without using protected link L• Q space: set of nodes that can reach destination D without using protected linkL
• Enforcing loop-freeness on post-convergence path• Where can I release the packet?
At the intersection between the post-convergence shortest path and the Q space• How do I reach the release point?
By chaining intermediate segments that are assessed to be loop-free
Topology Independent LFA – Implementation
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Conclusion
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• Simple routing extensions to implement source routing
• Packet path determined by prepended segment identifiers (one or more)
• Data plane agnostic (MPLS, IPv6)
• Network scalability and agility by reducing network state and simplifying control plane
• Traffic protection with 100% coverage with more optimal routing
Conclusion