net.add_addr_allfibs=1 behaviour deprecation

[Alexander V. Chernikov]

18.07.2020, 14:22, "Alexander V. Chernikov" <melifaro at freebsd.org>:
> Dear FreeBSD users,
>
> I would like to make net.add_addr_allfibs=0 as the default system behaviour and remove net.add_addr_allfibs.
> To do so, I would like to collect use cases with net.add_addr_allfibs=1 and multiple fibs, to ensure they can still be supported after removal.
>
> Background:
>
> Multi-fib support was added in r178888 [1], 12 years ago. Addition of interface addresses to all fibs was a feature from day 1.
> The `net.add_addr_allfibs` sysctl  was added in r180840 [2], 12 years ago.
>
> Problem:
> The goal of the fib support is to provide multiple independent routing tables, isolated from each other.
> `net.add_addr_allfibs` default tries to shift gears in the opposite direction, unconditionally inserting all addresses to all of the fibs.
>
> It complicates the logic, kernel code and makes control plane performance decrease with the number of fibs.
> It make impossible to use the same prefixes in multiple fibs, which may be desired given shortage of IPv4 address space.
>
> I do understand that there are some cases where such behaviour is desired.
> For example, it can be used to achieve VRF route leaking or binding on address from different fibs.
> I would like to collect such cases to consider supporting them in a different way.
>
> The goal is to make net.add_addr_allfibs=0 default behaviour and remove net.add_addr_allfibs.
> It will simplify kernel fib-related code and allow bringing more fib-related features. It will also improve fib scaling.
No objections has been received.
Next steps:
* Switch net.add_addr_allfibs to 0 ( https://reviews.freebsd.org/D26076 )
* Provide an ability to use nexthops from different fibs
* Remove net.add_addr_allfibs
> Timeline:
> Aug 1: summarising feedback and the usecases, decision on proceeding further
> Aug 20 (tentative):  patches for supported usecases
> Sep 15 (tentative):  net.add_addr_allfibs removal.
>
> [1]: [base Contents of /head/sys/net/route.c](https://svnweb.freebsd.org/base/head/sys/net/route.c?revision=178888&view=markup)
> [2]: [base Diff of /head/sys/net/route.c](https://svnweb.freebsd.org/base/head/sys/net/route.c?r1=180839&r2=180840&)
>
> /Alexander