Computing Segment for Service Routing in SAN

Introduction

Service Identification in SAN In order to deliver responsive services to clients, computing resources continuously migrate and spread from central sites to edge nodes. As shown in Figure 1, multiple instances located distributedly in different resource pools are capable of providing services. Compared with applying traditional IP routing protocols, a fine-grained service routing policy is capable of achieving optimal and efficient invocation of both computing power and the network.

Computing Power Networks |<---------Network-------->|<----------Cloud---------->| ]]> In order to implement service routing, the network should be aware of specific services and a service awareness network framework is introduced in . Within the proposed network framework, a service identification is defined as a SAN ID(Service ID) in to represent a globally unique service semantic identification. As mentioned in , a SAN ID is encapsulated in a SAN header which can be carried as an option in the IPv6 Hop-by-Hop Options Header, Destination Options Header and a type of SRH TLV. Since services provisioning requires delicate coordination among the client, network and cloud and thus simply encapsulating SAN header among packets delivery can hardly satisfy various practical situations:

The Destination Options header is used to carry optional information that need be examined by the destination of the path which is defined in , SAN header will only be resolved by the destination node. When a multi-layer service routing strategy is applied in the network domain, a quantity of relay nodes besides the destination are also required to identify SAN ID and forward the received packet accordingly as well. Thus, simply carring a SAN header can not fulfill a multi-layer service routing procedure.
When a SAN header is carried as an option in the IPv6 Hop-by-Hop Options Header, it may be processed by each nodes. Practically, not all nodes along the delivery path of the packet are capable of identifying and processing a SAN header. The SAN header may be changed accidentally and the packet may even be discarded in the forwarding process.
The Segment Routing Header (SRH) and the SRH TLV is defined in . Since the segment list is encoded in order, it indicates that the service routing process and successive forwarding behaviours must be orchestrated in advance. However, previous orchestration brings visible restrictions to the flexibility and adaptability of service routing.

To achieve a SAN header being processed in need in the network domain and to preserve its identifiability along the path from the client to the server, a new Segment to specify and standardize node behaviours is urgently required.

Service Routing in SAN As shown in Figure 2, a service routing table is designed to establish a mapping relationship between the SAN ID and the conventional IP routing table.

Service Routing in SAN |Routing| | | Table | | +-------+ v +-------+ |Service| |Routing| | Table | +-------+ +--------+ +-----------+ +----------+ +-----+ | Client +--------+Ingress PE+----------+Egress PE+--------+ L B | +--------+ +-----------+ +----------+ +-----+ ]]> A service routing table can be published from a control and management system to the network domain within a centralized control plane while it can also be calculated and generated by the Ingress PE itself under a distributed control plane. With considerations of path metrics, computing status and service SLA requirements, a specific service routing table is introduced, including mutiple attributes, SAN ID and outer gateway for instance. Afterwards, a corresponding IP routing table should be indexed which further determines the next hop or an SRv6 policy. In order to describe and standardize the mentioned behaviours, a new Computing Segment is proposed. With Computing Segments, multiple nodes in the network domain can be informed to identify and resolve SAN header in need and to implement a referred forwarding behaviour through the complete procedure.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Terminology

SAN: Service Aware Network
SAN ID: Service Aware Network Identification, an identification designed to indicate the fundamental and common service types
SAN header: Encapsulation format of the SAN ID
DOH: Destination Options Header
HBH: Hop-by-Hop Options Header
SRH: Segment Routing Header
SID: Segment Identifier
FIB: Forwarding Information Base
DA: Destination Address
LB: Load Balancer

Computing Segment This draft introduces a new SRv6 Segment, namely Computing Segment, aiming to describe the behaviour of querying service routing table and corresponding packet forwarding. Computing Segment is the identifier of packets in which a corresponding SAN header should be identified and further being forwarded via the matched service routing table entity, indicating the following operations:

Identify the SAN ID encapsulated in DOH, HBH or SRH TLV.
Query the service routing table indexed by SAN ID.
Update destination address accordingly.
Push a new IPv6 header with possible SRH containing the list of segments of the SRv6 policy.
Forward the packet.

In the case of SRv6, a new behavior End.C for Computing Segment is defined. Behaviours of End.C are described in the following sections.

When the SAN ID is encapsulated in the DOH When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does: (1) If the traffic is steered into a tunnel, an SRv6 policy for instance:

When the SAN ID is encapsulated in the DOH: Part 1 max_LE) or (Segments Left > Last Entry+1)) { S14. Send an ICMP Parameter Problem to the Source Address with Code 0 (Erroneous header field encountered) and Pointer set to the Segments Left field, interrupt packet processing, and discard the packet. S15. } S16. Decrement Segments Left by 1 S17. Update IPv6 DA with Segment List[Segments Left] S18. } S19. else { S20. Update IPv6 DA with the queried gateway S21. } S22. Push a new IPv6 header with its own SRH containing the list of segments of the SRv6 policy S23. Set the outer IPv6 SA to itself S24. Set the outer IPv6 DA to the first SID of the SRv6 policy S25. Set the outer Payload Length, Traffic Class, Flow Label and Next Header fields S26. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination ]]> (2) If the traffic is steered in a BE manner: The line S07 and lines from S22 to S24 are replaced by the following:

When the SAN ID is encapsulated in the DOH: Part 2

When the SAN ID is encapsulated in the HBH When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does: (1) If the traffic is steered into a tunnel, an SRv6 policy for instance:

When the SAN ID is encapsulated in the HBH: Part 1 max_LE) or (Segments Left > Last Entry+1)) { S14. Send an ICMP Parameter Problem to the Source Address with Code 0 (Erroneous header field encountered) and Pointer set to the Segments Left field, interrupt packet processing, and discard the packet. S15. } S16. Decrement Segments Left by 1 S17. Update IPv6 DA with Segment List[Segments Left] S18. } S19. else { S20. Update IPv6 DA with the queried gateway S21. } S22. Push a new IPv6 header with its own SRH containing the list of segments of the SRv6 policy S23. Set the outer IPv6 SA to itself S24. Set the outer IPv6 DA to the first SID of the SRv6 policy S25. Set the outer Payload Length, Traffic Class, Flow Label and Next Header fields S26. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination ]]> (2) If the traffic is steered in a BE manner: The line S07 and lines from S22 to S24 are replaced by the following:

When the SAN ID is encapsulated in the HBH: Part 2

When the SAN ID is encapsulated in the SRH TLV When an IPv6 node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as a SID (S), and S is a Computing SID, N does: (1) If the traffic is steered into a tunnel, an SRv6 policy for instance:

When the SAN ID is encapsulated in the SRH TLV: Part 1 max_LE) or (Segments Left > Last Entry+1)) { S10. Send an ICMP Parameter Problem to the Source Address with Code 0 (Erroneous header field encountered) and Pointer set to the Segments Left field, interrupt packet processing, and discard the packet. S11. } S12. Decrement IPv6 Hop Limit by 1 S13. Decrement Segments Left by 1 S14. Update IPv6 DA with Segment List[Segments Left] S15. Resolve the SAN ID encapsulated in the HBH, DOH or a type of SRH TLV S16. Maintain the SAN Header in the HBH, DOH or a type of SRH TLV S17. Query the service routing table indexed by SAN ID to determine an outer gateway and an according SRv6 policy S18. Push a new IPv6 header with its own SRH containing the list of segments of the SRv6 policy S19. Set the outer IPv6 SA to itself S20. Set the outer IPv6 DA to the first SID of the SRv6 policy S21. Set the outer Payload Length, Traffic Class, Flow Label and Next Header fields S22. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination S23. } ]]> (2) If the traffic is steered in a BE manner: The lines from S17 to S20 are replaced by the following:

When the SAN ID is encapsulated in the SRH TLV: Part 2

Use Case When a SAN header is carried as an option in the DOH, a typical service routing procedure is shown in Figure 9.

Typical Service Routing Procedure with Service ID Encapsulated in the DOH Suppose the Endpoint behaviour of END.C is configured at Ingress PE and Egress PE, namely SID 1 and SID 2 respectively. SID1 and SID2 are advertised in the network domain by IGP. The client registers with the management and operation system to acquire a SAN ID and encapsulates it in the packet. The initial destination is END.C (SID 1) which may be configured in a static routing manner. The service addressing procedure from the client to the cloud is described below:

The Computing SID of Ingress PE (SID1) is configured as DA. The packet carrying the SAN header as the option of the DOH is forwarded to Ingress PE.
When Ingress PE receives the packet, it identifys that DA is a Computing SID (SID1). As defined in 4.2, the Ingress PE determines the next hop for service routing which is END.C (SID 2) and updates DA. Ingress PE encapsulates an outer IPv6 header and continues to forward the packet carrying the DOH.
When Egress PE receives the packet, it identifys that DA is a Computing SID (SID2). As defined in 4.2, the Egress PE determines the next hop for service routing which is DIP which represents a specific service instance and updates DA. Egress PE further continues to forward the packet carrying the DOH.
When an intra-cloud LB receives the packet, the packet can be forwarded in a service routing manner or be processed in a native IP way, depending on the practical circumstances.

Outer Headers Encapsulated between Ingress PE and Egress PE |<-------------------Network----------------->|<-Cloud->| +------+ +----------+ +---------+ +-----+ |Client+-----+Ingress PE+-------------------+Egress PE+-----+ L B | +------+ +----------+ | +---------+ +-----+ BE: v TE: +-----------+ +-----------+ | IIP | | IIP | +-----------+ +-----------+ | SID | | SID | +-----------+ +-----------+ | SIP | | SRH | +-----------+ +-----------+ |END.C(SID2)| | SIP | +-----------+ +-----------+ | DOH | |END.C(SID2)| +-----------+ +-----------+ | PAYLOAD | | DOH | +-----------+ +-----------+ | PAYLOAD | +-----------+ ]]> As shown in Figure 10, between Ingress PE and Egress PE, an outer header including SRH should be encapsulated when the traffic follows a specific SRv6 TE policy. Otherwise, a normal IPv6 header should be encapsulated under a BE condition.

Security Considerations Security has always been an indispensable and significant consideration for design and innovation in the fields of communication and services provisioning. A Computing Segment as END.C defined in this draft may be given security semantics and according behaviours, including encryption and decryption, etc. Security considerations may be studied in the future work.

Acknowledgements TBA.

IANA Considerations This document requires registration of End.C behavior in "SRv6 Endpoint Behaviors" sub-registry of "Segment Routing Parameters" registry.