1. Service Chaining using MPLS Source Routing draft-xu-mpls-service-chaining-00
Xiaohu Xu & Stewart Bryant (Huawei)
Hamid Assarpour (Broadcom)
Himanshu Shah (Ciena)
Luis M. Contreras (Telefonica I+D)
Daniel Bernier （Bell Canada）

2. Introduction
Service Function Chaining steers a packet through an ordered set of Service Functions.
At ingress a classifier selects the Service Function Path and prepends this path to the packet.
There is great similarity between this operation and the use of source routed tunnels as developed in SPRING.
In this draft we show how the source routing approach using stacked MPLS labels developed for SPRING may be used to implement an SFC path.
This is method is a “Transport-Derived SFF” (Section of [RFC7665] )

3. Encoding SFP as a Label Stack
SFFs are MPLS Segment Routing Nodes
Advertise Nodal SIDs for themselves (NSID)
Advertise local label for each attached Service function (SF SID)
Classifier imposes label stack comprising ordered set of NSID and SF SID on packet.
LSRs forward to SFF using Nodal (or Adjacency) SIDs, SFF directs packet to Service Function based on SF SID
This approach is suitable as replacement for any “traditional” i.e. hard-wired service function chain.
No change to data-plane required.

4. The Passage of a Packet SFF1 SFF2 SC Z SF1 SF2 SF3 SR/SFC Domain
Packet to Z
1002
103
1001
101
SF1
SF2
SF3
The packet is selected to travel through an SFP {SFF1->SF1->SFF2->SF3}.
SR/SFC Domain
SID:101
SID:102
SID:1001
SID:1002
SID:103

5. IP Connectivity
Where connectivity is fully or partially IP, then one of a number of MPLS over IP tunnels can be used to interconnect SFFs:
RFC4023 (MPLS/IP or MPLS/GRE)
RFC7510 (MPLS/UDP)
RFC4817 (MPLS/L2TPv3)
Since the underlay can be IPv4, IPv6 or MPLS the solution is transport independent

6. Packet of a Packet in an IP Backbone
SFF1
SFF2 SC Z
Packet to Z
1002
103
1001
101
SF1
SF2
SF3
The packet is selected to travel through an SFC {SF1, SF3}.
SR/SFC Domain
SID:101
SID:102
SID:1001
SID:1002
SID:103
IP (SC->SFF1)
IP (SFF1->SFF2)
This label would be striped if it’s a PHP label.

7. Next Steps
We think this is an interesting approach that allows the majority of the SFC functionality to be instantiated using existing h/w. We would appreciate comments and contributions to the work.
We next need to look at the signalling.
Which WGs needs to progress this?