Radv proto sending adverts on wrong interface

[Kees Meijs | Nefos]

Hi,

On 13-03-2023 05:52, dxld at darkboxed.org wrote:
> It looks like made a mistake when testing my patch. It does in fact 
> not fix
> the problem. I then did some more reading of the linux scriptures and it
> turns out PACKET_OUTGOING ("Out" in tcpdump) should actually be 
> reliable so
> that meant that the "M" means that packet is actually coming in from the
> outside.
>
> Lo and behold I had an unintentonal, but at glance harmless, vlan
> configuration on the switch both enp1s0 and enp2s0 are connected
> to.
>
> Essentially enp2 is untagged vlan 1 and enp1 is untagged vlan 4 and tagged
> vlan 1 on the switch side. When sending the (untagged) RA on enp2 then I
> would expect to receive this with a vlan 1 tag on enp1 which would have
> made it obvious what is going on, but no it was coming in untagged.
>
> Smells like a switch bug[1] to me or maybe I don't understand 802.1Q 
> VLANs as
> well as I thought...
>
> Sorry for the noise.

About VLAN configuration: I guess one should never ever use VLAN_DEFAULT 
c.q. VLAN 1 at all. Vendors often think differently about this case, 
sometimes allowing to have a .1Q tag, sometimes not. Or sort of "both" 
as well. In combination with protocols such as LACP or (variations on) 
STP resulting in great fun, which of course is very sarcastic.

My two cents after opening up a box with a new switch, starting your 
configuration: explicitly disable VLAN1 and continue using others. Same 
goes for VLAN > 4090 by the way. These numbers are sometimes "reserved".

Cheers,
Kees