05 - IDNOG04 - Bambang Gunawan (Juniper) - Segment Routing

1. Segment Routing
Bambang Gunawan. System Engineer
bgunawan@juniper.net

2. Agenda
• Segment Routing Basic
• Segment Routing Use Case
• Segment Routing Deployment

3. Introduction
E V O L U T I O N
LDP
RSVP-TE
• Source Routing
• Uses existing MPLS Data
Plane (Packet format)
• Same MPLS label operation
(Push, Swap & Pop)
• SR currently only for
Transport label
SDN ReadyAddress existing protocols
weaknesses
• LDP is simple but has no TE
capability
• RSVP provide TE capability
without a good scaling
(midpoint state problem)
• Segment Routing was built
for SDN

4. How can SR get rid of LDP & RSVP-TE?
• LDP
– By using OSPF/IS-IS extensions to distribute label
– OSPF Opaque LSA & IS-IS new TLV
• RSVP
– By using global index/SID (SRGB + index)
– Thus source router can steer the path by stacking the desired segments

5. Global and Local Segments
• Global Segment
– The related instruction is supported by all the SR- capable nodes in the domain. In
the MPLS architecture, a Global Segment has a globally-unique index (SRGB +
Index)
• Local Segment
– The related instruction is supported only by the node originating it

6. Segment Types
• IGP Segments
– Prefix Segments
• Node Segment
• Anycast Segment
– Adjacency Segments
• IGP segment attached to an unidirectional adjacency or set of adjacencies
• BGP Segments
– Peer Node Segments
• BGP prefix segment which identifies a specific router (e.g. a loopback)
– Peer Adjacency Segments
• BGP segment attached to an unidirectional adjacency
– Peer Set Segments
• BGP segment attached to a set of adjacencies

7. IGP Segment Types
2
3
1 CE2
5
4
24024
CE1
16001
16002
16003
16004
16005
24035
24013
24012
24045
16024
16035
Node SID
Anycast SID
Adjacency SID

8. Use Case of Segment Routing
• Disjointness
• BGP On-Demand Next-hop
• BGP Egress Peer Engineering (EPE)
• Integration with PCE Controller

9. Disjointness
B
Z
11 13
12 14
21 23
22 24
A
SID: 16111 SID: 16111
SID: 16111 SID: 16111
SID: 16222 SID: 16222
SID: 16222 SID: 16222
SID: 16065
MP-BGP
16111
16065
IP packet

10. BGP On-Demand Next-hop
2
3
1 CE2
5
4
50
15
CE1
B: 20/8
NH: CE2
20/8 must receive low-latency service
PE4 tags 20/8 with community “Low-Lat”
B: 20/8
NH: PE4
Comm: Low-Lat
20.0.0.1/24
Default IGP cost: 10
Default TE cost: 10

11. BGP On-Demand Next-hop
2
3
1 CE2
5
4
50
15
CE1
MAP: Low-Lat means “minimize TE metric”
COMPUTE: minimize TE metric to node 4
RESULT: SR-TE: push [16002, 24024] Lowest TE metric path
TE cost 20
BGP: 20/8 NH PE4 (path-type TE-LL) (best)
FIB: BGP: 20/8 via 30001
FIB: SRTE: (PE4 –TE-LL)
Binding SID: 30001: Push [16002, 24024]
20.0.0.1/24
Default IGP cost: 10
Default TE cost: 10
SRTE policy’s
Binding SID

12. BGP EPE
3
16001 16002
AS 100
4
5
AS 200
AS 300
21
Flowspec BGP LS
16003
16004
16005
24023
24024
24052
24025
24234
24225
100
24225
IP packet
Peer
Node
Peer Adj Peer Set
Northstar Controller

13. Integration with PCE Controller
A1
B1
A3
B3
A4
B4
A6
B6
C2 C5
A2 A5
B2 B5
AS X AS Y (Backbone)
Northstar Controller
v v

14. SR Deployment Scenario
• Green-field deployment
• Always consider to run SR only for green-field deployment
• Integration with existing MPLS Core
• All nodes currently running support SR
• Upgrade OS to enable SR Support
• Configure SR on OSPF/IS-IS
• Monitor label allocation has been fully populated
• Switch label preference to SR
• Some nodes doesn’t support SR
• Do as above for SR ready island
• For non SR island:
• Have one (preferably more node) running as mapping server to map LDP to SR label

15. Mapping Server
A1
B1
A3
B3
A4
B4
A6
B6
C2 C5
A2 A5
B2 B5
SR only LDP only
Northstar Controller
v v
Mapping Server to map A5, A6, C5, B4, B5,
B6 SID to SR only island

16. Thank You