Policy Based Routing (PBR)

Referred site(s):

https://www.slideshare.net/khnog/policy-based-routing-pbr

https://www.cioby.ro/2016/09/08/configuring-policy-based-routing-on-cisco-asa/

https://www.internetworks.in/2018/11/policy-based-routing-pbr.html

https://www.cbtnuggets.com/blog/certifications/cisco/networking-basics-how-to-configure-policy-based-routing-on-cisco-routers

https://my-techie-guy.blogspot.com/2018/03/how-to-configure-forwarding-policy-on.html

Overview:

Policy based routing is use for path manipulation. It is used for implementing policy that causes the packet to take a different direction. Policy based routing allows source based routing. Routing table is destination base.

PBR is an alternative to destination based routing by overwriting/ignoring routing protocol based next hop decision.Normally next hop is decided based on destination address in the incoming packet.In PBR, packets are forwarded based on policies manually defined by network administrators.



 

Advantages of policy based routing:

Forwarding policy is useful in many real life traffic or production environments. The most popular use cases include:
1. If you want to direct traffic to a proxy server
2. If you want to redirect traffic to HTTP page or server (HTTP-Redirect) - not covered in this example.
3. Policy Based Routing (PBR) - where you forward traffic to a next hop (router or server)

 
4. Forwarding traffic to a cache server 
5. Forward traffic to a content optimizer or content accelerator (say for TCP acceleration)

6.Different users can reach the destination from different direction, hence load sharing

Networks have grown in complexity due to factors such as the cloud, mobility, and web-based applications. Not to mention, there’s more video and voice data running on those same networks. As a result, there’s an increased need to prioritize and segregate traffic on our networks.

Policy-based routing is a powerful feature that allows for nearly limitless customization in routing patterns. Essentially, the administrator identifies a type of traffic (web, VoIP, FTP, etc.) and then sets the predetermined routing pattern of that traffic.
Customization even extends into times of day, IP subnets, and every other possible variation

How to do it!

The first step in policy-based routing is to create an access list, which helps to filter traffic through your network.  

Select action for ACL as policy based routing

Next, create the route map/next hop that will segregate the traffic.  

Important points:

1. To check if PBR has been successfully implemented on a certain path, trace packet path using 'traceroute' command

2. PBR should be used with caution because if used improperly it can cause asymmetric routing in the environment