grout use-cases for host traffic

[Robin Jarry]

Hi Christoph,

Christoph, May 23, 2026 at 12:30:
> is grout limited to forwarding use-cases only or is it also possible to 
> reach the Linux host via a grout interface? (inbound and outbound)
>
> If so where can I find documentation for how to setup grout <-> linux 
> host services communication for TCP/UDP communication?

Yes, TCP/UDP termination is supported. This is what allows FRR daemons
to exchange routes with other peers. See this presentation from the DPDK
summit for more details (slide 7):

https://hosted-files.sched.co/dpdksummit2026/f3/frr-grout-dpdk-summit-2026.pdf

However there are a few caveats:

grout.service runs with a private netns, control plane linux TUN/TAP
interfaces will be created there. If you need Linux host services to be
reachable via grout interfaces, you need to run them with grout netns.

Example:

systemctl edit --stdin frr.service <<EOF
[Service]
JoinsNamespaceOf=grout.service
EOF

Alternatively, you can disable the network isolation for the grout
service.

systemctl edit --stdin grout.service <<EOF
[Service]
PrivateNetwork=false
EOF

NB: If you rely on this for SSH, mind that restarting grout will
interrupt all active connections.

There is no TSO/GRO support for TCP termination via grout. If you need
high performance (nginx or any other high bandwidth use cases), you
should use direct termination via another Linux interface (a virtual
function on the same NIC can work).

-- 
Robin

> No animals were injured.