A comparison of segment routing data-plane encodings
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Segment Routing provides simplified packet forwarding by encoding forwarding instructions as segments rather than per-flow state. This document compares different encodings of segments: 32-bit segments encoded directly in MPLS or UDP over IPv4/IPv6 (SRoMPLS, SRoUDP); and 128-bit segments encoded in a new IPv6 extension header (SRv6). SRoMPLS and SRoUDP are well-suited for brownfield networks as they can reuse existing MPLS and IP infrastructure with minimal overhead. SRv6 is designed for native IPv6 but has higher overhead. All approaches simplify operations but have different performance implications depending on the network environment.
![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](https://image.slidesharecdn.com/20190410v3acomparisonofsegmentroutingdata-planeencodings-190412130726/85/A-comparison-of-segment-routing-data-plane-encodings-8-320.jpg)
A comparison of segment routing data-plane encodings
- 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)
- 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
- 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 HMAC 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 HMAC 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 HMAC 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