SRv6 on Nokia SR OS¶
Nokia SR OS supports SRv6 in two forms: classic (full-length SIDs per RFC 8986) and micro-segment SRv6 (uSID), which Nokia describes as an extension of the SRv6 network-programming model rather than a replacement. Both can run on the same router at the same time, and Nokia's application note states that uSIDs and classic SIDs can be combined in the same segment list — keeping most of the path compressed while still carrying a full-length service or function SID where needed. SRv6 first shipped in SR OS 21.5.R2 on FP4-based hardware (IS-IS, VPRN, Flex-Algo, LFA/TI-LFA); EVPN-IFL followed in 22.5.R1 and EVPN-VPLS/VPWS and SRv6 policies in 22.7.R1.
Key Characteristics¶
| Aspect | Detail | Source |
|---|---|---|
| SID modes | Classic SRv6 and micro-segment SRv6 concurrently on one platform; SIDs of each type must come from different SID blocks | SR OS 26.7 user guide |
| Mixing in a segment list | uSID containers and classic SIDs can be used together in one segment list | Application note |
| Classic SID length | Variable: 32-bit, 16-bit or 128-bit | Application note |
| uSID container | 32-bit block carrying up to six 16-bit uSIDs; uSIDs are global (node) or local (adjacency, service, function) | Application note |
| uSID allocation | global-sid-entries (default 16) splits the 16-bit space: 0x0000-0x3FFF global, 0x4000-0xFFFF local; block-length must be identical network-wide | SR OS 26.7 user guide |
| Maximum SID depth | The application note quotes up to 9 classic SIDs or 47 uSIDs including primary path, LFA backup and service SID. The configurable limit per SR policy segment list is 7 classic segments or 24 micro-segments (42 uSIDs with pre-compressed containers) | Application note; SR OS 26.7 user guide |
| Coexistence | Classic SRv6, uSID and MPLS/SR-MPLS enabled together on the same router, service or IP interface | Application note |
Behaviors (SR OS 26.7)¶
| Mode | Behaviors |
|---|---|
| Micro-segment | uN and uA (advertised by IS-IS); uDT4, uDT6, uDT46, uDX2, uDT2U, uDT2M (BGP services or static) |
| Classic | End and End.X (with PSP/USP/USD flavors), End.DT4, End.DT6, End.DT46, End.DX2, End.DT2U, End.DT2M; End.B6.Encaps.Red as the SR policy binding SID |
| Headend | H.Encaps.Red and H.Encaps.L2.Red only (plain H.Encaps and H.Encaps.L2 are not supported); H.Insert.Red for LFA repair |
| Not supported | End.T, End.DX4, End.DX6 |
Services and Traffic Engineering¶
| Area | Supported (classic and uSID) |
|---|---|
| L3 services | Base-router BGP routes, VPRN (IP-VPN), EVPN-IFL |
| L2 services | EVPN-VPLS and EVPN-VPWS with single-active or all-active multihoming |
| Multicast | Tree-SID SRv6 (replication segments) for NG-MVPN I-PMSI/S-PMSI, first documented in 25.3: static CLI configuration, classic SIDs only, no LFA or BFD protection (see Multicast) |
| IGP | IS-IS, including Flex-Algo |
| TE | Flex-Algo; SRv6 policies configured statically or via the BGP SR Policy address family (22.7.R1), or from a PCE over PCEP (RFC 9603, first documented in 26.7) |
| IGP extras | IS-IS MT0 and MT2; microloop avoidance for SRv6 (first documented in 26.3); BGP-LS export of SRv6 information (IS-IS only) |
| OAM | Ping and traceroute to SRv6 SIDs, VRF prefixes and SRv6 policies |
| Protection | LFA, remote LFA, TI-LFA (link, node, SRLG); SR OS originates and terminates repair tunnels with H.Insert.Red and can terminate H.Encaps.Red repair tunnels from other vendors |
| Gateway | Interworking between MPLS, SR-MPLS, SRv6 classic, SRv6 uSID, VXLAN and MPLS-over-UDP at transport and service layers |
Multi-vendor TI-LFA
SR OS builds TI-LFA and remote-LFA repair tunnels with H.Insert.Red, while some other implementations use H.Encaps.Red. The SR OS guide describes a termination mode to accept encapsulated repair tunnels — check this when mixing vendors in one IGP domain. See TI-LFA.
Platforms¶
The SR OS 26.7 Segment Routing and PCE User Guide's SRv6 chapter applies to the 7450 ESS, 7750 SR, 7950 XRS and VSR. Nokia's advanced configuration guides add the hardware condition: SRv6 "is supported on FP4-based equipment in SR OS Release 21.5.R2 and later", and the EVPN chapters require FP4-based network ports. The application note covers "Nokia routing platforms" generically.
SR Linux (Nokia's data-center NOS) is a separate implementation: its SRv6 chapter first appears in SR Linux 26.3 and lists the 7730 SXR and the 7220 IXR-H5/H6, the latter as basic uSID transit nodes for AI back-end fabrics. EVPN-VPLS (MAC-VRF) over SRv6 is not supported there.
Further Reading¶
- Implementations Overview
- SRv6 Support Matrix - SR OS feature by feature next to IOS-XR, Junos, EOS, VRP and open-source platforms
- uSID Compression - How uSID containers and shift-and-forward work
- Interworking & Migration - MPLS/SRv6 gateway designs
- EVPN Multihoming - All-active EVPN over SRv6
References¶
- Nokia: Segment Routing IPv6 (SRv6) on Nokia routing platforms — Application note - 2024 application note: uSID as an extension of SRv6, mixing uSID and classic SIDs, services, TE, protection, gateway
- Nokia SR OS 26.7 Segment Routing and PCE User Guide: Segment routing with IPv6 data plane (SRv6) - Official SRv6 configuration guide: classic and micro-segment modes, behaviors, IS-IS, BGP services, TI-LFA
- RFC 9800 - Compressed SRv6 Segment List Encoding (NEXT-C-SID, the IETF form of uSID)
- Nokia Advanced Configuration Guide: Segment Routing with IPv6 Data Plane - SRv6 on FP4-based equipment from SR OS 21.5.R2
- Nokia SR OS 26.7 Multicast Guide: SR P2MP policy - Tree-SID SRv6 for NG-MVPN and its restrictions
- Nokia SR Linux 26.7 Segment Routing Guide: SRv6 - SR Linux SRv6 platforms and features