Policy-Based Routing - Cisco Catalyst 4500 Series Software Configuration Manual

Layer 3 Software Features
OSPF for Routed Access supports only one OSPFv2 and one OSPFv3 instance with a maximum number
Note
of 1000 dynamically learned routes.
With the typical topology (hub and spoke) in a campus environment, where the wiring closets (spokes)
are connected to the distribution switch (hub) forwarding all nonlocal traffic to the distribution layer, the
wiring closet switch does not need to hold a complete routing table. Ideally, the distribution switch sends
a default route to the wiring closet switch to reach inter-area and external routes (OSPF stub or totally
stub area configuration).
Refer to the following link for more details:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/routed-ex.html
With Cisco IOS Release 12.2(53)SG, the IP Base image supports OSPF for routed access. The Enterprise
Services image is required if you need multiple OSPFv2 and OSPFv3 instances without route
restrictions. Enterprise Services also is required to enable the VRF-lite feature.

Policy-Based Routing

Traditional IP forwarding decisions are based purely on the destination IP address of the packet being
forwarded. Policy-Based Routing (PBR) enables forwarding based upon other information associated
with a packet, such as the source interface, IP source address, Layer 4 ports, and so on. This feature
allows network managers more flexibility in how they configure and design their networks.
Starting with Release IOS XE 3.4.0SG and IOS 15.1(2)SG, the PBR Recursive Next Hop feature
enhances route maps to enable configuration of a recursive next-hop IP address. The recursive next-hop
IP address can be a subnet that is not directly connected. The routing table will be looked up to find the
directly connected next-hop to which to send the packet so that it is routed via the recursive next-hop
that has been configured.
For more information on policy-based routing, see
Unicast Reverse Path Forwarding
The Unicast Reverse Path Forwarding (Unicast RPF) feature helps to mitigate problems that are caused
by the introduction of malformed or forged (spoofed) IP source addresses into a network by discarding
IP packets that lack a verifiable IP source address.
For information on URPF, see
Unidirectional Link Routing
Unidirectional link routing (UDLR) provides a way to forward multicast packets over a physical
unidirectional interface (such as a satellite link of high bandwidth) to stub networks that have a back
channel.
For information on configuring unidirectional link routing, refer to the URL
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/15.1SY/config_guide/sup720/ude_udl
r.html
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
1-22
Chapter 42, "Configuring Policy-Based Routing."
Chapter 37, "Configuring Unicast Reverse Path Forwarding."
Chapter 1 Product Overview