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User is unable to configure PBR on a Catalyst 3550 switch

Core Issue

Catalyst 3550 switches use Switch Database Management (SDM) templates to configure memory resources in the switch and optimize support for specific features, depending on how the switch is used in the network. One of the four available templates can be chosen to specify how system resources are allocated. This affects the maximum number of unicast MAC addresses, Internet Group Management Protocol (IGMP) groups, Quality of Service (QoS) Access Control Entries (ACEs), security ACEs, unicast routes, multicast routes, routed interfaces and Layer 2 (L2) VLANs that can be configured on the switch. 

To configure Policy-Based Routing (PBR) on the Catalyst 3550 switch, the SDM template must be modified to enable the switch to support the 144-bit Layer 3 (L3) Ternary Content Addressable Memory (TCAM). Without this template, the switch allows a route-map command to be created and applied to an interface. This is done by issuing the ip policy route-map command. However, it does not show up in the configuration and PBR is not effective.

Resolution

To resolve this issue, perform these steps:

  1. To configure the Catalyst 3550 switch to support the 144-bit L3 TCAM and enable PBR, issue the sdm prefer command from global configuration mode.

      This command reformats the TCAM space allocated to unicast routing in the current template by reducing the number of supported unicast routes by half.

  

      extended-match

2.   For the new template to be effective, issue the reload command from privileged EXEC mode.

For more information, refer to the Configuring Policy-Based Routing section of Configuring IP Unicast Routing on Catalyst 3550 switches.

How PBR is Configured to Forward Packets

Setting the next hop IP address

Setting the outgoing interface

Source

Multiple devices

Source and Destination Physical Connectivity

Source and destination exist on different subnetwork

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