Computing Segment for Service Routing 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.

|<---------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 delivered from cloud need 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 routing protocol is applied in the network domain, a quantity of relay nodes besides the destination are 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 modified and changed 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 must be orchestrated in advance which indicates various endpoint behaviours in order to successively implement the designated service routing. Previous orchestration should be regarded to be severe restrictions. 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.

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.

|Routing|<->|Routing| | Table | | 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 both path metrics 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 locate and identify SAN header in need and to implement a referred forwarding behaviour through the complete procedure.

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.

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

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 forwarding table entry indexed by SAN ID. Forward the packet to the new destination. In the case of SRv6, a new behavior End.C for Computing Segment is defined. An instance of a Computing SID is associated with a service routing table and a source address. Behaviours of End.C when a SAN header is carried as an option in the HBH, DOH or a type of SRH TLV are described in the following sections.

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:

When an SRv6-capable node (N) receives an IPv6 packet whose destination address matches a local IPv6 address instantiated as an SRv6 SID (S), and S is a Computing SID, N does:

0) { S03. Decrement IPv6 Hop Limit by 1 S04. Decrement Segments Left by 1 S05. Update IPv6 DA with Segment List[Segments Left] S06. Identify the SAN ID encapsulated in the SRH TLV S07. Query the forwarding table entry indexed by SAN ID S08. Set the packet's associated FIB table to the specific FIB S09. Maintain the TLVs in the SRH S10. Resubmit the packet transmit to the new destination S11. } S12. } ]]> When a SAN header is carried as a type of SRH TLV, Computing SIDs in Segment List are required to be orchestrated in advance which previously indicates the the determinism of a multi-segment routing policy. Therefore, Computing Segment does not cooperate well with the circumstances when a SAN header is carried as a type of SRH TLV.

When a SAN header is carried as an option in the DOH, a typical service addressing procedure is shown in Figure 6.

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 to the nodes in the network by IGP. The service addressing procedure from the client to the cloud is described below: The Computing SID of Ingress PE (SID1) is configured as DA by the client. The packet carrying the SAN header as the option of the DOH is forwarded to Ingress PE. When Ingress PE receives the packet, it queries the local routing table in accordance with DA and identifys that DA is a Computing SID (SID1). As defined in 4.2, the Ingress PE continues to forward the packet carrying the DOH. When Egress PE receives the packet, it queries the local routing table in accordance with DA and identifys that DA is a Computing SID (SID2). As defined in 4.2, the Egress PE continues to forward the packet carrying the DOH. When an intra-cloud LB receives the packet, the packet can be forwarded in accordance with the Endpoint behaviour defined in 4.2. or be processed as a normal IPV6 packet, depending on the practical circumstances.

|<-------------------Network----------------->|<-Cloud->| +------+ +----------+ +---------+ +-----+ |Client+-----+Ingress PE+-------------------+Egress PE+-----+ L B | +------+ +----------+ | +---------+ +-----+ BE: v TE: +-----------+ +-----------+ | IIP | | IIP | +-----------+ +-----------+ | EIP | | SID | +-----------+ +-----------+ | SIP | | SRH | +-----------+ +-----------+ |END.C(SID2)| | SIP | +-----------+ +-----------+ | DOH | |END.C(SID2)| +-----------+ +-----------+ | PAYLOAD | | DOH | +-----------+ +-----------+ | PAYLOAD | +-----------+ ]]> As shown in Figure 7, 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. In the introduced case, the SAN header is not perceived by relay devices between Ingress PE and Egress PE.

TBA

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