Policy-Based Routing With Object Tracking - Cisco Catalyst 4500 Series Software Configuration Manual

Policy-Based Routing
route-maps (each containing ACLs with permit ACEs only) may require 6-7 minutes of flatten time
before programming into hardware. This process may repeat if an adjacency change requires PBR
reprogramming.

Policy-Based Routing with Object Tracking

Beginning in Cisco IOS XE Release 3.8.0E and Cisco IOS Release 15.2(4)E, you can configure
Policy-Based Routing (PBR) to use object tracking, to verify the most viable next-hop IP address to
which to forward packets, using an Internet Control Message Protocol (ICMP) ping as the verification
method. PBR used with object tracking is most suitable for devices that have multiple Ethernet
connections as the next hop. Normally, Ethernet interfaces connect to digital subscriber line (DSL)
modems or cable modems, and do not detect a failure upstream in the ISP broadband network. The
Ethernet interface remains up, and any form of static routing points to that interface. Using PBR with
object tracking allows you to back-up two Ethernet interfaces, determine the interface that is available
by sending ICMP pings to verify if the IP address can be reached, and then route traffic to that interface.
To verify the next-hop IP address for the device, PBR informs the object tracking process that it is
interested in tracking a certain object. The tracking process, in turn, informs PBR when the state of the
object changes.
Restrictions for Policy-Based Routing with Object Tracking
The set next-hop verify-availability command is not supported with the following:
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IPv4 and IPv6 Policy-Based Routing for VRF Instances
Virtual routing and forwarding (VRF) allows multiple routing instances in Cisco software. Beginning in
Cisco IOS Release XE 3.7 0E and IOS 15.2(3)E, the Policy-Based Routing (PBR) feature is VRF-aware
and works on multiple routing instances, beyond the default or global routing table.
Incoming packets are filtered through the match criteria that are defined in the route map. After a
successful match occurs, the set command configuration determines the VRF through which outbound
packets are policy routed.
Inherit-VRF, Inter-VRF, Global-to-VRF, and VRF-to-Global Routing
The Policy-Based Routing feature supports inherit-VRF, inter-VRF, and VRF-to-global routing.
With inherit-VRF, packets arriving at a virtual routing and forwarding (VRF) interface are routed, by
looking-up the same VRF's routing table.
With inter-VRF routing, packets arriving at a VRF interface are routed, by looking-up a different VRF's
routing table, as specified by the set command.
With VRF-to-global routing, packets arriving at a VRF interface are routed via the global routing table.
With global-to-VRF routing, packets arriving at the global interface (an interface that is not part of a
VRF) are routed via a VRF routing table.
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
42-6
VRF instances
Virtual switching system (VSS)
IPv6 traffic
Chapter 42 Configuring Policy-Based Routing