RIB Policy

Routing Information Base (RIB) Policy provides ability to police the computed routes before programming in underlying hardware. Currently supported use-case is to modify weight parameter for each next-hop. However, it can be extended in future to support changing admin-distance (aka route priority), add or drop next-hops, change route metric, and block route from programming or re-distribution.

Flow Diagram

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Decision module in Open/R implements the RIB Policy processing. The RIB Policy applied on computed routes just before they’re sent off for programming.

Creating RIB Policy

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RIB Policy is expressed in thrift specification and is defined as struct RibPolicy in OpenrCtrl.thrift. Please refer to the documentation associated with the defined structs for details.

At a high level RIB Policy consists of two parts, Matcher (Selection) and Action (Transformation). The matcher specified criteria for route selection on which action is to be performed. Action specifies the transformation intent. One such pair of Match-Action is termed as RibPolicyStatement. Multiple such statements can be specified. However, note that only first matching action will be applied.

Setting RIB Policy

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RIB Policy can be set via RPC API (aka thrift API). It is not supported to be set via configuration as of now. Following three APIs provide set, and get of RibPolicy as well as clearing or resetting functionality of the same. It is important to note that policy have ttl_secs field which specifies the validity of policy, beyond which it is expired and effects of policy will be reverted.

// Set policy API
void setRibPolicy(1: RibPolicy ribPolicy) throws (1: OpenrError error)

// Get policy API
RibPolicy getRibPolicy() throws (1: OpenrError error)

// Clear policy API
void clearRibPolicy() throws (1: OpenrError error)

SetRibPolicy example code is provided for reference in terms of how to define and set RibPolicy.

For more details refer to OpenrCtrl service interface in OpenrCtrl.thrift.

UseCase - NextHop Weight Transformation (UCMP)

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Define and achieve policy driven weighted distribution of flows over multiple next-hops. This could be useful in context where the correctness of forwarding state (aka routes) comes from the distributed protocols, but the operator wants to influence the traffic flows as per congestion in the network (e.g. send more to less congested part of network).

RIB Policy allows operators to customize the weight for computed next-hops. As of now the weights can be customized per area or per neighbor fields. The neighbor weight takes precedence over the area weight. See RibRouteActionWeight struct in OpenrCtrl.thrift for more information.

The next-hops that are processed through RIB Policy and get assigned weight=0 will be removed. If policed routes have no next-hop, then they will be removed from RIB. This won’t be programmed nor will they get re-distributed across the areas.

Configuration Knob

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RibPolicy is by default disabled and RPC APIs will throw exception if an application tries to set the policy. This is a safety mechanism to disable this feature where it is not needed. You’ll need to set the enable_rib_policy field in OpenrConfig to true to make use of RibPolicy feature.

CLI

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Breeze CLI provides a command to view the currently configured RibPolicy.

$ breeze decision rib-policy
> RibPolicy
  Validity: 291s
  Statement:
    Prefix Match List: ::/0
    Action Set Weight: default=0, area-weights={'0': 1}