Policy-Based Routing (PBR), How PBR works and How we can use PBR?

PBR:

• Destination based routing systems make it quite hard to change the routing behavior of specific traffic. With PBR, a network engineer has the ability to dictate the routing behavior based on a number of different criteria other than destination network, including source or destination network, source or destination address, source or destination port, protocol, packet size, and packet classification among others.
• Policy-based routing adds flexibility and control that other routing techniques do not. It give you a level of control that a routing protocol by itself does not.
• With flexibility, there is typically a cost and in this case its scalability and manageability.
• It is a great tool but not one to be used for all cases. When you have a need to forward base on something other than destination, then PBR is your answer.
• In a way, it allows traffic engineering at interface level. It allows to route the packets over specific traffic engineered paths, which provide the desired QoS through the network.

OSPF Series 11: Everything on Redistribution: Part 2- Redistribution into OSPF, Pitfall of Redistribution (Administrative Distance, Route Feedback)

Everything on Redistribution: Part 2- Redistribution into OSPF, Pitfall of Redistribution (Administrative Distance, Route Feedback)

 

Redistributing into OSPF

OSPF is a standardized Link-State routing protocol that uses cost (based on bandwidth) as its link-state metric. An OSPF router performing redistribution automatically becomes an ASBR

OSPF Series 10: Everything on Redistribution: Part 1- Basics, RIP, IGRP, EIGRP, Static and Connected

Everything on Redistribution- Basics, RIP, IGRP, EIGRP, Static and Connected

Route Redistribution Basics

It is preferable to employ a single routing protocol in an internetwork environment, for simplicity and ease of management. Unfortunately, this is not always possible, making multi-protocol environments common.

Route Redistribution allows routes

OSPF Series 9: Route Filtering and Route-Maps

Prefix-Lists

Prefix-lists are used to match routes as opposed to traffic. Two things are matched:

• The prefix (the network itself)

• The prefix-length

OSPF Series 8: Prefix Lists

Prefix Lists

Example 1)

access-list 1 permit 1.2.3.0 0.0.0.255

ip prefix-list LIST permit 0.0.0.0/0 le 32

This means:

Check the first 0 bits of the prefix 0.0.0.0 The subnet mask must be less than or equal to 32