Re: [RFC] mac80211: add extap functionality

[Felix Fietkau <nbd@openwrt.org>]

On 2016-02-17 12:55, Grzegorz Bajorski wrote:
> Client interface briding was only possible when 4addr frames were used with
> a 4addr/WDS aware AP. It was not possible to do it otherwise due to 3addr
> frame limitation.
> 
> The extap logic introduces a smart MAC address masking/translation
> (including modyfing packets beyond SA/DA, e.g. DHCP broadcast flag is set).
> 
> There are still some unsolved problems and bugs:
>  - due to bridge port routing and sk_buff payload sharing skb_copy() is
>    performed; this ideally should be reworked
>  - ipv6 support is still not finished
>  - extap is enabled by default currently; it should be configurable via
>    nl80211 the same way 4addr is
> 
> There's also an idea to move this as a generic link driver (just like
> macvlan, et al) which would allow unmodified cfg80211 drivers to enjoy the
> extap functionality. Thoughts?
> 
> Note: This changes cfg80211 file in this single patch only for reviewing
> convienence.
> 
> This is an early draft to solicit comments on the design.
> 
> Signed-off-by: Grzegorz Bajorski <grzegorz.bajorski@tieto.com>
You can get a lot of the same effect (sharing the same subnet between
hosts behind multiple interfaces and having forwarding between them)
without any changes to mac80211.

OpenWrt uses a daemon called 'relayd' which I wrote some years ago. It
does ARP translation, DHCP packet mangling and sets up policy routing to
forward packets between multiple interfaces.

You can find it here:
http://git.openwrt.org/?p=project/relayd.git;a=summary
git://git.openwrt.org/project/relayd.git

Since you can cover the same use cases with user space code, I don't
think it's a good idea to put bridge emulation hacks in the kernel's
wireless stack.

- Felix