Optimizing Traffic with Junos' Filter-Based Forwarding

In the world of network engineering, traffic optimization is a critical aspect that ensures efficient network performance. One of the ways to achieve this is through Filter-Based Forwarding (FBF) in Junos. This blog post will provide a detailed guide on how to optimize traffic using FBF, a topic that is essential for students studying for the JNCIS-ENT certification.

What is Filter-Based Forwarding?

Filter-Based Forwarding is a Junos feature that allows network engineers to route packets based on criteria other than the destination IP address. This is particularly useful in situations where you need to route traffic through different paths based on specific conditions such as source address, protocol, or even application type.

How does Filter-Based Forwarding work?

FBF works by applying firewall filters to incoming traffic. These filters match certain criteria in the packet headers and then apply an action to the packets that match. The action could be to accept, discard, or route the packet through a specific routing instance.

Configuring Filter-Based Forwarding

Let's dive into how to configure FBF on a Junos device. For this example, we'll assume that we want to route all HTTP traffic through a specific routing instance.

First, we need to create a firewall filter that matches HTTP traffic:

set firewall family inet filter FBF term 1 from destination-port http
set firewall family inet filter FBF term 1 then routing-instance HTTP-traffic

In the above configuration, we're creating a filter named 'FBF' with one term. This term matches all packets with a destination port of HTTP (port 80) and then routes them through the 'HTTP-traffic' routing instance.

Next, we apply this filter to the incoming interface:

set interfaces ge-0/0/0 unit 0 family inet filter input FBF

In this command, we're applying the 'FBF' filter to the incoming traffic on the ge-0/0/0 interface.

Finally, we need to ensure that the 'HTTP-traffic' routing instance has a default route pointing to the desired next-hop:

set routing-instances HTTP-traffic routing-options static route next-hop

In this command, we're setting a default route in the 'HTTP-traffic' routing instance that points to the next-hop IP address


Filter-Based Forwarding is a powerful tool in the Junos toolbox that allows for granular control over traffic routing. By understanding and implementing FBF, network engineers can optimize network performance and ensure that traffic is routed in the most efficient manner possible.

Remember, the key to mastering FBF (or any networking concept) is practice. So, get hands-on with your Junos devices and experiment with different FBF configurations. Good luck with your JNCIS-ENT certification studies!

In the next blog post, we will delve into more advanced Junos topics. Stay tuned!

© Ben Jacobson.RSS