What is This?

There are use cases where it is desirable to isolate network forwarding and control plane functions into a dedicated Linux netns. For instance, a routing appliance with a management interface and several interfaces that are only for forwarding network traffic.

These systemd units make it easy to create a netns, attach the desired interfaces, and start FRR.

Why Not Use DPDK+FRR?

The objective of this configuration is not primarily performance, but simplicity. It's much easier to attach a network interface to a netns than it is to configure it to use DPDK (if it's supported). Also, recent Linux kernels have very good forwarding performance, in some cases as good as what DPDK can offer. So, it made sense for my use-case to do it this way.

Why Not Use VRF?

It takes longer to set up, and, by default, VRF's don't run in their own netns, so one loses the benefit of the implicit security context that a netns affords. It is possible to have VRF's inside of a netns, but that is beyond the scope of this setup.

Audience

The user of this document is expected to have experience with SystemD-based Linux distributions.

Setup

1. Install FRR

Follow the FRR docs to install for your distro.

Ensure FRR service is stopped:

systemctl stop frr.service

2. Identify Interfaces

Create a list of interfaces that will be dedicated to routing. The names will vary depending on distribution. In our example, we'll use enps0f0 and enps0f1.

3. Copy The Units

netns Template Unit File and FRR Unit Drop-In

sudo mkdir -p /etc/systemd/system/frr.service.d; \
sudo cp ./frr.service.d/frr.conf /etc/systemd/system/frr.service.d/frr.conf; \
sudo cp [email protected] /etc/systemd/system/[email protected]

Interface Units

For each interface identified in step 2, copy [email protected] template unit file, replacing example int the filename with the interface name:

sudo cp [email protected] /etc/systemd/system/[email protected]; \
sudo cp [email protected] /etc/systemd/system/[email protected]

4. Enable Services

sudo systemctl enable [email protected]; \
sudo systemctl enable [email protected]; \
sudo systemctl enable [email protected]; \
sudo systemctl enable frr.service

5. Modify FRR Unit Drop-In

Edit the FRR unit drop-in configuration to add the interfaces we identified in step 2.

sudo nano /etc/systemd/system/frr.service.d/frr.conf

Change this:

### MODIFY
[email protected]
[email protected]
###

To this, matching our example:

### MODIFY
[email protected]
[email protected]

[email protected]
[email protected]
###

6. Rerfresh SystemD

sudo systemctl daemon-reload

7. Start FRR

sudo systemctl start frr.service

8. Confirm

The result of this command:

sudo ip netns exec frr ip link

Should now list the interfaces we attached to the netns

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enps0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
3: enps0f1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff

9. Finish

Configure FRR as required.