Many network operators still struggle with which type of data-plane encoding they should use for segment routing. The world is hyper-connected and we can’t afford to be late to deliver 5G. Using IPv6, MPLS (or even IPv4) data-plane encoding keeps us moving forward.

1. 1 © Nokia 2019
A Comparison of Segment Routing Data-plane
Encodings
Service enablement based upon segments (32bit or 128bit)
• Gunter Van de Velde
• 11-04-2019

2. 2 © Nokia 2019
• Introduction
• Evolution of Segment Routing
• Conclusion
Agenda

3. 3 © Nokia 2019
Market needs
Network adapts for application and user experience
Simple architecture
***
Reduced state
in the network
***
Ease of operation
Segment
Routing
Doesn’t scale for
newest network
services and
adaptive network
behavior
Current
Architecture
Policy Mapping, RSVP, LDP,
Policy Based Routing, …
Policy imposed directly upon
each payload packet Pick your poison

4. 4 © Nokia 2019
Segment Routing
Value Proposition – Simplicity by “Enhanced Forwarding Behavior”
• Packet Forwarding decision is based upon “Segments”
and not upon “IP payload prefix”
• Segments are encoded as 32bits or 128bits
- 32bit Segments supported IPv6, MPLS, (or even IPv4)
dataplane
- 128bit Segments supported only upon IPv6 dataplane
- Sequence of segments represents a set of actions/instructions
imposed to the packet
• No per-flow state contained within the network
• Segments are distributed by Routing or SDN control
- No more LDP, because LDP is “Soo Sad”
- Fair balance between “distributed intelligence” and “centralized
optimization/programming”
• Perfect complement to NSH (Network Services Header)
- However, minimal context could be encoded in segments (see
later)
© Nokia 2019

5. 5 © Nokia 2019
• Introduction
• Evolution of Segment Routing
• Conclusion
Agenda
A story to compare Apples with Apples !

6. 6 © Nokia 2019
• Do not confuse with MPLS !
- There is no ‘LDP’ with Segment Routing
• Segments encoded directly into MPLS Dataplane
• https://datatracker.ietf.org/doc/draft-ietf-spring-segment-routing/
• Principle used:
- Encode the Segments as a sequence of 32bit Label fields
• MPLS label itself is 20 bits added with 12 bit operational overhead/information
- Segments directly distributed by Routing Protocols or controllers (there is NO LDP)
- Build upon massive existing technology experience (Fast-Reroute, L2/3 Services support, etc…)
- Well known and documented security implications
• Minimal packet overhead imposed by Segment Routing (i.e. 32bit/segment)
• Mature dataplane technology well supported by Network vendors and Forwarding ASICs
• Technology sweet-spot: Reduce complexity in MPLS based networks
Evolution of Segment Routing # 1
Encoding: 32bits Segments directly into MPLS Dataplane
© Nokia 2019

7. 7 © Nokia 2019
How does segment Routing look like?
Using 32bit Segments (on dataplane it mimics MPLS)
32 bit per Segment SR Header
(MPLS Dataplane Encapsulation)
Segment Routing Payload
(e.g. original IP Packet)
Original
IP Header
Original
IP packet payload
(variable size)

8. 8 © Nokia 2019
• Do not confuse with classic IPv6 - This is NOT classic IPv6 Routing
• Segments encoded as [Outer IPv6 header] [SRH extension header] [optional HMAC security header]
• https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-16
• Principle used:
- Based upon IPv6 Source Routing with new innovative IPv6 extension header (SRH)
- Each segment is 128 bit
• 128bit segments allow limited service semantics to be encoded (NSH not absolutely required anymore)
• Larger header overhead tax compared to MPLS encoding
• IPv6-only data-plane support
• HW forwarding ASIC considerations
- Processing long extension headers is computationally expensive
• Security consideration: semantics mix of “location” and “context” is good topic for discussion
Evolution of Segment Routing # 2
Encoding: 128bits Segments directly into IPv6 Header

9. 9 © Nokia 2019
How does SRv6 Look like
Segments (128 bit) with IPv6 encapsulation
8 byte fixed SRH header
+
(X * 128 bit/segment
SRv6 Header
(IPv6 Dataplane Encapsulation)
Segment Routing Payload
(e.g. original IP Packet)
Original
IP Header
Original
IP packet payload
(variable size)
IPv6 Encapsulation
(Tunnel/Outer Header)
40 Byte (320 bit)
Optional HMAC (Security)40 Byte (320 bit)
SRH Extension Header

10. 10 © Nokia 2019
Encoding 128bit Segment
How does it look on the wire?
IP Packet (v4 or v6)
Provider Edge
Router
Provider BackboneCustomer Site or Data-Center
IP Packet (v4 or v6) SR Headers
IPv6-Only for SRv6IPv6/IPv4

11. 11 © Nokia 2019
Encoding 128bit Segment
How does it look on the wire?
IP Packet (v4 or v6)
Provider Edge
Router
Provider BackboneCustomer Site or Data-Center
IP Packet (v4 or v6) SR Headers
IPv6-Only for SRv6IPv6/IPv4
IP Packet (v4 or v6) IP Packet (v4 or v6)
SR Headers
HMA
C
SRH IPv6
Payload
40 byte 8 + (x * 16) byte 40 byte
SRv6

12. 12 © Nokia 2019
Encoding 128bit Segment
How does it look on the wire?
IP Packet (v4 or v6)
Provider Edge
Router
Provider BackboneCustomer Site or Data-Center
IP Packet (v4 or v6) SR Headers
IPv6-Only for SRv6IPv6/IPv4
IP Packet (v4 or v6) IP Packet (v4 or v6)
SR Headers
HMA
C
SRH IPv6
Payload
40 byte 8 + (x * 16) byte 40 byte
SRv6
Typical SRv6 overhead properties
Typically 8 bytes of overhead (4 bytes are mandatory)
Typically, another 16 bytes per SID
Routing header with 3 SIDs is 56 bytes long
Imposed bandwidth overhead
Short packets ( >500) bytes are common on the Internet
Routing header with three SIDS may become common
> 10% Routing header overhead
(https://datatracker.ietf.org/meeting/104/materials/slides-104-spring-the-ipv6-compressed-routing-header-crh-01)*Note1: Reference
*Note1 *Note1

13. 13 © Nokia 2019
Encoding 128bit Segment
Comparing 128bit vs 32bit encoding
IP Packet (v4 or v6)
Provider Edge
Router
Provider BackboneCustomer Site or Data-Center
IP Packet (v4 or v6) SR Headers
IPv6-Only for SRv6IPv6/IPv4
IP Packet (v4 or v6) IP Packet (v4 or v6)
SR Headers
HMA
C
SRH IPv6
Payload
40 byte 8 + (x * 16) byte 40 byte
SRv6
IP Packet (v4 or v6) IP Packet (v4 or v6)
SR Headers
Segments
Payload
4 byte/segment
MPLS

14. 14 © Nokia 2019
• What we discussed sofar
- We have 32bit segments encoded in MPLS dataplane
- We have 128bit segments encoded in IPv6 dataplane
• So, can we not have 32bit segments encoded using native IPv6 and IPv4?
Ofcours we can !!!
Evolution of Segment Routing
What is next?

15. 15 © Nokia 2019
• Support of 32bit SIDs for IP-based networks
• 32bit Segments encoded using UDP header
- Outer IPv4 header is 20byte (variable length) and IPv6 header is 40 byte (fixed)
- UDP header size is 8 Byte
- 32bit Segments sequence will look like MPLS labels
- Nothing new and existed for years for MPLS under the technology radar
• https://tools.ietf.org/html/draft-ietf-mpls-sr-over-ip-02
• Principle used:
- Encode the Segments as a sequence of 32bit Labels encoded inside UDP
- Build upon existing technology experience (MPLS), Fast-Path forwarding, Fast-Reroute
- Native support for IPv6 and IPv4 dataplane (NO flag day at operator)
- Well known and documented security implications
- Payload Meta-data is added using NSH (IETF SFC standard technology)
Evolution of Segment Routing # 3
Encoding: 32bits Segments directly in SRoUDP (v4 or v6)

16. 16 © Nokia 2019
How does SRoUDP Look like
Segments (32 bit) with IP encapsulation
Don’t forget about NSH Meta-Data
Applications use it
(=16 byte for NSH Type1)
(>16byte for NSH type 2)
32 bit per Segment SR Header
(MPLS Dataplane Encapsulation)
Segment Routing Payload
(e.g. original IP Packet)
Original
IP Header
Original
IP packet payload
(variable size)
UDP Transport HeaderUDP Header
IP Tunnel Encapsulation HeaderIP Outer (Tunnel) Header
NSH
8 byte UDP Header
40 byte (IPv6) or 20 byte (IPv4)

17. 17 © Nokia 2019
How does SRoUDP compare with SRv6?
Comparing the encoding
Each segment
is 32 bit
Original
IP Header
Original
IP packet payload
(variable size)
UDP Header
IP Tunnel Header (v4 or v6)
Optional NSH
8 byte fixed
40 byte (IPv6)
or 20 byte (IPv4)
8 byte fixed SRH header
+
(X * 128 bit/segment)
Original
IP Header
Original
IP packet payload
(variable size)
IPv6 Encapsulation
(Tunnel Header)
40 byte
Optional HMAC (Security)40 Byte
SRH Extension Header
Optional NSH
SRv6 (128 bit segments) SRoUDP (32 bit segments)
SRv6 can use a 128bit
Segment encoding
for limited meta-data

18. 18 © Nokia 2019
Comparing the encoding: Use-case perspective
Approved for Native IPv6 Data-plane transport
RFC8354: Use Cases for IPv6 SPRING

19. 19 © Nokia 2019
How does SRoUDP compare with SRv6?
Comparing the encoding
>10% BW overhead for
500byte packets w/ 3 SID
+-4% BW overhead for
500byte packets w/ 3 SID
SRv6
Fixed SRH + 3 * SID
8Byte + 3*16Byte
56 Byte
11.2% BW overhead
SRoUDP
UDP header + 3 * SID
8Byte + 3*4Byte
20 Byte
4% BW overhead
For a 500Byte Payload
(https://datatracker.ietf.org/meeting/104/materials/slides-104-spring-the-ipv6-compressed-routing-header-crh-01)*Note1: Reference

20. 20 © Nokia 2019
• Seamless Segment Routing support for
- Native IPv6 dataplane (SRoUDPv6)
- Native MPLS dataplane
- (and even native IPv4 Dataplane (SRoUDPv4))
• A Segment Routing 32bit-Segment is mapped to most appropriate data-plane encapsulation
(performance, security, availability)
- Part of Nokia NF-IX (Network Function Interconnect Framework)
- NFIX uses predominant BGP (BGP-LS, BGP-LU, BGP SR-TE, EVPN etc…) as the dominant protocol
- NFIX segment routing underlay: Advanced LFA, SRTE tunnels, scale optimization, SDN controller driven
- Note: Nokia NFIX architecture allows SRv6 as well if needed/required
• Deployment scenario
- Sweet spot: Brownfield networks (Fixed and Mobile providers)
- Easy integration of existing L2/3 and resiliency services
- Deploy proven/secure technology first and seamlessly optimize when appropriate to different types of segments
Evolution of Segment Routing - 4
Seamless Segment Routing Encoding

21. 21 © Nokia 2019
• Introduction
• Evolution of Segment Routing
• Conclusion
Agenda

22. 22 © Nokia 2019 Confidential
• SRoMPLS & SRoUDP (32bit segments) run over MPLS/IPv4/IPv6
- Good fit for brownfield networks
• Can keep using existing MPLS, IPv4 and IPv6 dataplane
• No need for forklift upgrade
• Seamless across all dataplanes
- Small BW overhead imposed by Segment Routing
- Forwarding ASIC friendly
- Well documented security properties
• SRv6 (128bit segments) runs over IPv6 network
- Innovative technology fit for IPv6 networks
- 128bit segments could contain service/context properties
• Simplification: SRv6 may use industry standard NSH header, but not a must anymore
- Ongoing work progressed at IETF
- Processing long extension headers is computationally expensive
• Be aware of forwarding ASIC limitations
Conclusion
Segment Routing Data-plane encoding
© Nokia 2019