Segment Routing over IPv6
SR applied to the IPv6 data plane — segment lists encoded as a sequence of IPv6 addresses in an SRH extension header, enabling source routing without MPLS labels or additional encapsulation overhead.
SRv6 SID List Forwarding
A packet traverses three SR endpoints. The SID list is encoded directly in the IPv6 destination address — each hop pops the active uSID and forwards on the next.
What SRv6 Is
SRv6 (RFC 8986) encodes a source-initiated path as an ordered list of IPv6 addresses called SIDs — each representing a topological instruction (segment) at a specific node. The Segment Routing Header (SRH, RFC 8754) carries the SID list in the IPv6 extension header stack. At each SR node, the active SID is processed, the SL (Segments Left) pointer is decremented, and the IPv6 DA is updated to the next SID.
SRv6 SIDs are routable IPv6 addresses structured with a Locator (topologically significant prefix, typically /48 or /64) and a Function (behavior identifier). This means SR forwarding state is embedded in the IPv6 routing table — no separate label space, no LFIB, no MPLS-specific HW resources. Transit nodes need no SRH awareness unless they are SR endpoints.
SRv6 uSID (RFC 9252) compresses the SID encoding significantly: multiple micro-SIDs are packed into a single 128-bit IPv6 address, reducing per-hop processing and header overhead to levels competitive with SR-MPLS in typical SP deployments.
SRv6 Network Programming
RFC 8986 defines a set of SRv6 endpoint behaviors — End (SR endpoint), End.X (endpoint with cross-connect), End.T (endpoint with table lookup), End.DT4/DT6/DT46 (endpoint with decap and L3 table lookup). These behaviors implement the full VPN forwarding function within the SID semantics, enabling L3VPN and L2VPN services over a pure IPv6 core.
OcNOS-SP Implementation
IS-IS SRv6 Extensions
IS-IS with SRv6 extensions (draft-ietf-lsr-isis-srv6-extensions). Locator advertisement, SID sub-TLV per prefix. Flexible Algorithms for topology-aware SID assignment.
uSID Compression
RFC 9252 uSID implementation. /32 block, /48 locator. Multiple uSIDs packed per 128-bit address. Compatible with existing IPv6 forwarding HW — no SRH processing at transit.
H.Encaps Behavior
Head-end encapsulation inserting a new IPv6 outer header with SRH. H.Encaps.Red for reduced SRH (single SID). Supports policy-based steering by match criteria.
SRv6-TE Policies
SRv6 traffic engineering policies with explicit SID lists. PCE-computed paths via PCEP. BGP SR-TE for cross-domain policy distribution.
L3VPN over SRv6
End.DT46 behavior for decap and VRF lookup. BGP L3VPN with SRv6 transport (RFC 9252). Per-VRF SID allocation from Locator block.
SR-MPLS Co-existence
SRv6 and SR-MPLS active simultaneously on the same node. Per-VPN transport plane selection. Interworking function for cross-domain stitching at domain boundaries.
OcNOS-Validated Hardware
For reference only. The platforms below are a representative subset of SRv6-validated hardware. The complete, current list of qualified platforms — with ASIC, port density, and version coverage — is maintained in the OcNOS Hardware Compatibility List.