[Bug 282673] ipfw tags are lost while transit via if_epair

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 20 Nov 2024 07:37:28 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=282673

Zhenlei Huang <zlei@FreeBSD.org> changed:

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                 CC|                            |zlei@FreeBSD.org

--- Comment #6 from Zhenlei Huang <zlei@FreeBSD.org> ---
(In reply to Mark Johnston from comment #4)
> Would it make sense for epair to preserve tags if the endpoints belong to the same VNET? 

Technically possible, and looks reasonable.

> That's a slightly odd configuration, but the reasoning for stripping tags doesn't apply there.

While I suggested bridge + epair + vlan configuration to intercept tagged
frames ( as in the following digram) in a bug report [1] about bridge. It is
clear and promising.

tap0  ---                                 --- epair0b.5
em0   --- bridge0 --- epair0a --- epair0b --- epair0b.10
igc0  ---                                 --- epair0b.20

I'm not sure if that is commonly deployed but I think it is not an odd
configration but rather a **workaround** / **solution** .

I do not use IPFW but it seems the man doc
> Tags are kept with the packet everywhere within the kernel, but are lost when
> the packet leaves the kernel
is outdated. I think preserving tags within the same VNET is applicable.

1. https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240106#c31

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