On 15 Dec 2015, at 9:49, 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 and B 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
There isn’t a universal way to do this, since all that a bridge (and a
switch is just a particular case of bridge, for the purposes of this
argument) does is copy ethernet frames from one port/segment to another.
You might be lucky enough to have switches/bridges with some smarts
which you can query or otherwise take advantage of, but then you’re
into environment-specific things.
If you are, for example, able to obtain SNMP access to each device, you
might be able to simple ask what the interface types are and dump any
bridging tables etc.
A bit hacky and non-ideal, you could try to look for known-wired and
known-wireless MAC addresses and take that as a hint as to what’s
going on. It relies on having stations on those networks which have
vendor OUI’s you’d not expect to see on anything but a particular
interface type.
d.
