Hi Emiliano and Pieter,
Thanks for reporting this issue. Can you try enabling the tap plugin in
your startup.conf? E.g. add 'plugin tap_plugin.so { enable }' to the end of
the plugins stanza. Native tap support was moved from libvnet to a plugin
for 26.02. tap_create_if() was changed from being a libvnet symbol that is
linked directly to an inline function that tries to find the tap_create_if
symbol in tap_plugin.so and store it in a function pointer. If the symbol
lookup fails because the tap plugin is not loaded, args->error is set to
indicate that there was an error, but args->rv is not set to an error
value. The value of args->rv being less than 0 is how lcp_itf_pair_create()
determines whether tap_create_if() failed. Since rv is left as 0,
lcp_itf_pair_create() believes that tap_create_if() succeeded and calls
vnet_sw_interface_set_mtu() using the value args.sw_if_index, which was
initialized to ~0. Hilarity ensues.
I could reproduce the issue with the tap plugin disabled and the problem
went away on my test system when I enabled the tap plugin and restarted
vpp. I'll try to work on better error handling & validation, but hopefully
updating startup.conf is sufficient to get you going in the meantime.
Thanks,
-Matt
On Tue, Mar 3, 2026 at 1:39 AM Pieter Meyer via lists.fd.io <pieteras.meyer=
[email protected]> wrote:
> I have seen a similar issue.
>
>
>
>
>
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