[dev] VRF support with netns

[Philippe Guibert]

Hi all,

About VRF support of frrouting 2.0, regarding [0], the following is indicated:
- VRF Lite (Linux VRF device support, Zebra and BGP) Instructions ([1])

This is good information that VRF lite is now supported in frrouting.
However, I would like to draw your attention to the following:
* the VRF feature in frrouting is lost for kernels not supporting [1],
whereas it was working on Quagga.
* it is not possible to rely on kernel netns, whereas in Quagga the
netns solution was used.
An issue has been created for that in [4].

On behalf of 6WIND, we want to fix those two issues, but would like to
ensure that the proposed solution is aligned, and does not conflict
with frrouting/other roadmap.

Code investigation in frrouting showed the following :
- The netns support has been moved to a lib/netns libary ( see commit
illustration in [2]). This change made useless the ns support )
- The VRF support has been mapped to vrf kernel feature ( as
illustrated in [3], file lib/vrf.h)

The most obvious solution is the following.
It consists in configuring at runtime frrouting, so that the frrouting
VRF mecanism will rely either on VRF or on Netns feature.

The fact is the clients that have a quagga based solution, would like
to benefit for frrouting, without having to change their
configuration. Either because the kernel is not yet up to date, or
because this is not part of their plan to move to vrf kernel
implementation. Like that, the user will be able to choose with a
minimum configuration change to be on VRF mode or on Netns mode.

Any remarks about the proposal to solve [4] ?

Best Regards,

Philippe

[0] https://github.com/FRRouting/frr/wiki/Quagga-1.1-%E2%86%92-FRR-2.0
[1] https://www.kernel.org/doc/Documentation/networking/vrf.txt
[2] https://github.com/FRRouting/frr/commit/13460c44a2241
[3] https://github.com/FRRouting/frr/commit/216b18efe144b
[4] https://github.com/FRRouting/frr/issues/385