Re: reliably detecting the presence of a bridge?

[Andrew McConachie <smutt () depht com>]

Flip a bit in the Ethernet FCS as it egresses deviceA. If the frame 
arrives with a correct checksum at deviceB, then there's a switch in the 
middle. Most modern switches recalculate FCS at egress port.

If the frame never arrives, most likely there is a switch in between. If 
the frame arrives with the broken FCS, there is no intermediate switch.

--Andrew

On 12/15/15 4:48 AM, Dave Taht wrote:
> I am curious if there is some sort of igmp or other form of message
> that would reliably detect if a switch had a bridge on it. How could
> deviceA detect deviceC was a bridge in this case?
>
> deviceA  -> ethernet switch -> deviceB
>                      ethernet switch -> deviceC with bridged wifi and ethernet
>
> question came up in the context of:
>
> http://lists.alioth.debian.org/pipermail/babel-users/2015-December/002231.html
>
> --
> Dave Täht
> Let's go make home routers and wifi faster! With better software!
> https://www.gofundme.com/savewifi