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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Introduction to Policy-based Routing

Introduction to Policy-based Routing

Definition

Policy-based routing (PBR) is a mechanism that makes routing decisions based on user-defined policies.

NOTE:
  • The differences between PBR and routing policy are as follows:
    • PBR implements routing based on packets. It routes data packets based on user-defined policies instead of following the routes in the existing routing table.
    • Routing policies implement routing based on routing information. Routing policies are used to filter routes and set route attributes. You can change route attributes (including reachability) to change a route over which network traffic is transmitted.

Purpose

Traditionally, devices searches routing tables for routes of packets based on their destination addresses and then forward the packets. Currently, more users require that devices route packets based on user-defined policies. PBR allows network administrators to make user-defined policies to change packet routes based on source addresses, packet size, and link quality in addition to destination addresses.

Benefits

PBR has the following advantages:

  • Allows network administrators to make user-defined policies for routing packets, which improves flexibility of route selection.
  • Allows different data flows to be forwarded on different links, which increases link usage.
  • Uses cost-effective links to transmit service data without affecting service quality, which reduces the cost of enterprise data services.

Implementation

PBR applies only to packets received from other devices, but not to locally generated packets such as local ping packets.PBR is valid only for IP packets.

The device does not support PBR-based tracert. When the device receives a tracert packet, it discards the packet if it has only PBR but not a routing entry for the destination IP address of the packet.

PBR is implemented based on the redirect action configured in a traffic behavior and takes effect only on the inbound packets. By default, a device forwards packets to the next hop found in the routing table. If PBR is configured, the device forwards packets to the next hop specified by PBR.

When the device forwards packets to the next hop specified by PBR, the device triggers ARP learning if it has no ARP entry corresponding to the IP address of the specified next hop. If the device cannot learn this ARP entry, it forwards packets to the next hop found in the routing table. If the device has this ARP entry, it forwards packets to the next hop specified by PBR.

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Updated: 2019-08-09

Document ID: EDOC1000041694

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