Introduction
At present, common SRV6 SIDs are primarily categorized as path or service SIDs. For instance, End and End.X SIDs signify nodes and links, respectively, while End.DT4 and End.DT6 SIDs designate IPv4 and IPv6 VPN instances, correspondingly.
As services continue to evolve, the introduction of a broader array of service SIDs has become commonplace. The table below described the service SIDs most frequently in use.
Common SIDs table
| SID | DESCRIPTION | PROTOCOL | TYPE |
| End SID | Designates an endpoint SID that identifies a destination IGP node. Its corresponding function is to revise the IPv6 Destination Address and subsequently scrutinize the IPv6 Forwarding Information Base (FIB) for the purpose of packet forwarding. | IGP | PATH SID |
| End.X SID | Denotes a Layer 3 cross-connect endpoint SID, specifically earmarked for the identification of a link. The associated function involves the modification of the IPv6 Destination Address, followed by the conveyance of packets through the egress interface affiliated with the SID in question. | IGP | PATH SID |
| End.DT4 SID | The End.DT4 SID, on the other hand, serves as a PE-specific endpoint SID, primarily tasked with the identification of an IPv4 VPN instance. Its prescribed function encompasses the decapsulation of packets, succeeded by a diligent perusal of the routing table associated with the relevant IPv4 VPN instance to facilitate the onward journey of packets. This SID holds a functional equivalence to an IPv4 VPN label and finds its utility in L3VPNv4 scenarios. | BGP | SERVICE SID |
| End.DT6 SID | The End.DT6 SID designates a specialized endpoint SID that is tasked with identifying an IPv6 VPN instance. Its corresponding function involves the decapsulation of packets, followed by an extensive search through the routing table pertinent to the involved IPv6 VPN instance, with the ultimate objective of facilitating the forwarding of packets. Notably, this particular SID bears functional equivalence to an IPv6 VPN label and is extensively utilized in L3VPNv6 scenarios. | BGP | SERVICE SID |
| End.DX6 SID | End.DX6 SID serves as another PE-specific Layer 3 cross-connect endpoint SID, primarily dedicated to identifying an IPv6 CE. Its corresponding function entails the decapsulation of packets, followed by the onward transmission of the resulting IPv6 packets through the Layer 3 interface linked to the SID. Analogous to its counterparts, this SID is analogous to a label identifying an adjacency to a CE and is frequently utilized in L3VPNv6 scenarios. | BGP | SERVICE SID |
| End.DX4 SID | End.DX4 SID signifies a PE-specific Layer 3 cross-connect endpoint SID specifically earmarked for the identification of an IPv4 CE. Its designated function encompasses the decapsulation of packets, succeeded by the transmission of the resultant IPv4 packets through the Layer 3 interface associated with the SID. Remarkably, this SID holds a functional similarity to a label that designates an adjacency to a CE and finds extensive application in L3VPNv4 scenarios. | BGP | SERVICE SID |
| End.DX2 SID | End.DX2 SID denotes a Layer 2 cross-connect endpoint SID specifically assigned to identify an endpoint. Its corresponding function revolves around the decapsulation of packets, the removal of the IPv6 header, including all its associated extension headers, and the subsequent transmission of the remaining packet data to the outbound interface connected to the SID. Notably, this SID serves a crucial role in EVPN VPWS scenarios. | BGP | SERVICE SID |
| End.DX2L SID | Presence of a bypass tunnel within the network, an automatic generation of the End.DX2L SID takes place to further enhance network efficiency. | BGP | SERVICE SID |
| End.DT2U SID | A Layer 2 cross-connect endpoint SID is identified, necessitating a unicast MAC table lookup, with the primary purpose of designating an endpoint. Its corresponding function involves the elimination of the IPv6 header, inclusive of all associated extension headers. Subsequently, the MAC address table is scoured to identify a MAC entry based on the exposed destination MAC address, followed by the transmission of the remaining packet data to the corresponding outbound interface as per the entry. This particular SID finds utility in EVPN VPLS unicast scenarios. In the event of a bypass tunnel’s existence within the network, an End.DT2UL SID is generated automatically. This SID serves as a navigational guide for unicast traffic forwarding over the bypass tunnel, particularly in situations where a CE maintains dual-homing with PEs. | BGP | SERVICE SID |
| End.DT2M SID | Layer 2 cross-connect endpoint SID is introduced, necessitating broadcast-based flooding while pinpointing an endpoint. Its associated function lies in the removal of the IPv6 header, encompassing all of its extension headers. Following this, the remaining packet data is disseminated through the Bridge Domain (BD). This specific SID is pertinent in EVPN VPLS BUM scenarios. | BGP | SERVICE SID |
| End.OP SID | Lastly, we encounter the mention of an OAM SID, serving a unique function involving the transmission of OAM packets to the OAM process. This SID’s principal application lies in ping and tracert scenarios. | IGP | SERVICE SID |
Local SRv6 SID table
Each SRv6 node maintains a localized SID table encompassing all SRv6 SIDs originating from the node. An SRv6 FIB can be generated from this table. The localized SID table serves the following functions:
• Prescribes locally initiated SIDs, including but not limited to End.X SIDs.
• Defines directives linked to these SIDs.
• Archives routing information pertinent to these directives, including details on outbound interfaces and next-hop destinations.
Conclusion
In conclusion, the realm of common SRv6 SIDs, characterized by their versatility and significance, plays a pivotal role in the world of networking and communication. These SIDs, including but not limited to End and End.X SIDs, and the specialized End.DT4 and End.DT6 SIDs, serve as essential building blocks for efficient data routing, encapsulation, and VPN instance identification. As our technological landscape continues to evolve, the prominence of SRv6 SIDs in network architecture and service delivery is undeniable. Their usage represents a dynamic fusion of innovation and practicality, ensuring the seamless flow of data and the future of networking.