F5 – Working with Route Domains

In the world of networking, segregating traffic and maintaining isolated environments within a single piece of hardware is often crucial. F5 BIG-IP offers a feature known as Route Domains, which allows for this level of segregation. In this blog post, we will delve into what Route Domains are, how to use them, and the importance of understanding their ID numbering system.

What Are Route Domains?

A Route Domain in F5 BIG-IP is essentially an isolated routing table. This enables you to have multiple sets of network paths, or routing tables, within the same F5 system. Think of them as logical separations for network traffic, akin to VRF (Virtual Routing and Forwarding) in traditional networking.

One of the key benefits of using Route Domains is the ability to have overlapping IP address spaces. This is particularly useful in multi-tenancy environments or when migrating applications which might have the same IP address ranges.

Specifying Route Domain IDs

Each Route Domain is identified by a unique ID number. This ID is used to distinguish between different logical routing tables. When configuring IP addresses in F5, you will often see them appended with a `%` followed by a number, like this: ``. This tells the F5 system that this IP address should use the routing table associated with Route Domain ID 2.

Verifying Route Domain IDs

To verify or list the Route Domains configured on your F5 device, use the following TMSH (Traffic Management Shell) commands:

1. List all Route Domains:

    tmsh list net route-domain

2. List a specific Route Domain ID only (this is the command you should use):

    tmsh list net route-domain id

It is imperative to understand and use the correct Route Domain ID when configuring your F5 BIG-IP system. Specifying the correct ID ensures that traffic is routed based on the correct isolated routing table. This is particularly important when dealing with overlapping IP address spaces, as the Route Domain ID will determine the correct path for the traffic to take.

A Note on Naming Route Domains

One thing to note is that the Route Domain ID is always a number, and this cannot be changed. For instance, the default Route Domain has an ID of 0 (`%0`), and you cannot change this to a name like `Default`. Similarly, while you might want to change `%1` to something more descriptive like `RD1`, this is not possible. The Route Domain ID must be a number and is the only way to reference a specific Route Domain within the F5 system.


Route Domains are a powerful feature in F5 BIG-IP, allowing for traffic segregation and the use of overlapping IP address spaces. Understanding how Route Domain IDs work and ensuring their correct usage is crucial for the proper routing of traffic and the overall health of your network environment. While the ID system is strictly numeric and cannot be altered to descriptive names, keeping a well-documented record of what each Route Domain ID represents can aid in managing complex configurations.