SRH Extension for Redundancy Protection

Redundancy protection is a method of providing 1+1 protection by sending copies of the same packets of one flow over multiple paths, which includes packet replicaiton, elimination and ordering. This document defines SRv6 header(SRH) extensions to support redundancy protection.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . Redundancy Node: the start point of redudancy protection, which is a network device that could implement packet replication. Merging Node: the end point of redudancy protection, which is a network node that could implement packet elimination and ordering(optionally). Editor's Note: Similar mechanism is defined as "Service Protection" in the . In this document, we define a new term "Redundancy Protection" to distinguish with other service protection method. Some of the terms are the similar as .

The figure shows how to provide redundancy protection over SRv6.

|<---------------SRv6 Domain------------->|<----IPv6--- | | | +------+T2+----+ | +---+ +---+ +-+-+ +-+-+ +---+ +---+ | E1+----| In|--+T1+--+Red| |Mer|--+T4+--| Eg+----+ E2| +---+ +---+ +-+-+ +-+-+ +---+ +---+ +-----+T3+-----+ ]]> As the figure shows, an IPv6 flow is sent out from the end station E1. The packet of the flow is encapsulated in an outer IPv6+SRH header in the Ingress(In) and transported through an SRv6 domain. In the Egress(Eg), the outer IPv6 header+SR of the packet is popped, and the packet is sent to the destination E2. The process of redundancy protection is as follows: 1) The flow is replicated in Rep(Redundancy Node); 2) Tow replicated flows go through different paths till Mer (Merging Node); When there is any failures happened in one the path, the service continues to deliver through the other path without break; 3) The first received packet of the flow is transmitted from Mer (Merging Node) to Eg(Egress), and the redundant packets are eliminated. 4) Sometimes, the packet will arrive out of order because of redundancy protection, the function of reordering may be necessary in the Merging Node. This document defines Flow Identification and Sequence Number in Segment Routing Header(SRH) as an extension of the current draft to support redundancy protection. Flow Identification is used to distinguish flows and Sequence Number is used to distinguish packets in the same flow when doing packet merging and ordering.

Flow Identification and Sequence Number could be defined in SRH optional TLV.

where: Type: 8bits, to be assigned by IONA. Length: 8 octets. RESERVED: 28 bits, MUST be 0 on transmission and ignored on receipt. Flow Identification: 20 bits, which is used for identifying redundant protection flow.

where: Type: 8 bits, to be assigned by IONA. Length: 8. RESERVED: 20 bits. MUST be 0 on transmission and ignored on receipt. Sequence Number: 28 bits, which is used for indicating sequence number of the redundant protection flow.

where: Type: 8bits, to be assigned by IANA. Length: 8 octets. Flow Identification: 20 bits, which is used for identifying the redundant protection flow. Sequence Number: 28 bits, which is used for indicating sequence number of the redundant protection flow. Reserved: 32 bits. MUST be 0 on transmission and ignored on receipt.

TBD

Thank you for valuable comments from James Guichard and Andrew Mail