Redundancy Policy for Redundancy Protection

Redundancy Policy is used to enable packet replication and instantiation more than one active ordered lists of segments between redundancy node and merging node to steer the same flow through different paths in an SR domain.

A Redundancy Policy is identified through the tuple <redundancy node, redundancy ID, merging node>. Redundancy node is specified as IPv4/IPv6 address of headend of Redundancy Policy, which is the node to perform packet replication. Merging node is specified as IPv4/IPv6 address of endpoint of Redundancy Policy, which is the node to perform packet elimination. Redundancy ID could be a specified value of "color" define in section 2.1 of , which indicates the SR policy as a redundancy policy. Redundancy ID could also be used to distinguish redundancy policy sharing the same redundancy node and merging node. The following elements are extended in Redundancy Policy: Redundancy ID: is used to distinguish a redundancy policy or different redundancy policies Redundancy SID: is the Binding SID for a redundancy policy and defined in . Redundancy SID triggers the instantiation of a Redundancy Policy in the forwarding plane of redundancy node. Candidate path: more than one candidate paths are included in redundancy policy. In each candidate path, the last segment SHOULD be the Merging SID defined in . The preference of candidate paths in redundancy policy SHOULD be the same to instantiate more than one active ordered segment lists.

Redundancy policy inherates the basic structure and elements of SR Policy, the information model of Redundancy Policy is the following:

Candidate-path CP1 Preference 200 Priority 10 Weight W1, SID-List1 Weight W2, SID-List2 Candidate-path CP2 Preference 200 Priority 10 Weight W3, SID-List3 ]]> The Redundancy Policy POL1 is identified by the tuple <redundancy node, redundancy ID, merging node>, R1 is the redundancy node, and M1 is the merging node. Redundancy ID is used to identify as a redundancy policy in the context of redundancy node. Two candidate-paths CP1 and CP2 instruct the ordered segment lists, with the same definition of SR policy. Preference is mandatory for each candidate path and used to determine the parallel forwarding paths. Candidata paths with the same preference value are chosen as the disjoint forwarding path of redundancy protection. Since there is no tie-breaking rules of the only one valid best path selection, atrributes of protocol-origin and discriminator are not applicable in redundancy policy.

In Redundancy Policy, the preference of candidate path is used to select the valid active candidate paths. The preference of candidate paths in redundancy policy SHOULD be the same. Different from SR Policy, there is no tie-breaker comparison between candidate path with equal preference values. Redundancy Policy has no limit on the number of active CPs since more than one forwarding paths are required in order to perform redundancy protection. Regarding the instantiation of ordered lists of segments for candidate path, it keeps the same forwarding instantiation and behavior defined for SR policy. For example, traffic steered on POL1 is still flow-based hashed on Segment-List1 <SID11...SID1i> with a ratio W1/(W1+W2), so does Segment-List2. A packet is steered into a Redundancy policy at a redundancy node in following ways: Incoming packets have an active SID matching the Redundancy SID at the redundancy node. Per-destination Steering: incoming packets match a BGP/Service route which recurses on a Redundancy Policy. Per-flow Steering: incoming packets match or recurse on a forwarding array of where some of the entries are Redundancy Policy. Policy-based Steering: incoming packets match a routing policy which directs them on a Redundancy Policy.

In Redundancy Policy, each candidate path must be associated with a BSID. The endpoint behavior of BSID specifies the instantiation of Redundancy Policy in forwarding plane and adopts the endpoint behavior definition of Redundancy SID . The associated BSID of Redundancy Policy and its endpoint behavior are signalled redundancy node via BGP SR Policy or PCEP or Netconf YANG.