reliably detecting the presence of a bridge?

Dave Taht dave.taht at
Wed Dec 16 09:36:46 UTC 2015

On Tue, Dec 15, 2015 at 4:19 PM, William Herrin <bill at> wrote:
> On Tue, Dec 15, 2015 at 4:48 AM, Dave Taht <dave.taht at> 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?
> Hi Dave,
> Start with precision in language. An ethernet switch is one form of
> ethernet bridge although the reverse is not necessarily true. So, a
> switch is always a bridge by definition. Q.E.D.


> From what you've posted, you don't want to detect the difference
> between a switch and a bridge, you want to detect the difference

To be more clear I wanted to detect if there was more than one
bridge on the network, where the bridge being a PITA was a wired/wireless

> between a wired and wireless segment segment in the network. Is that
> correct? Any wireless link or just radio? Any radio link or just
> 802.11 wifi?

I believe the radios in this case were probably ubnt.

>Are you just trying to detect stations behind wireless or
> do you want to identify segments that are carried over wireless?

The latter.

In this case a routing optimization that works well on wired links was
enabled when there were wireless bridges on that segment, leading to
some chaos in the originally referenced thread.

The "right", slower, inefficient on wired, routing metric is the ETX
metric in that case, but knowing when to turn that on, automatically,
would be nice... which means somehow detecting there was a wireless
bridge on that network. So as no announcements of BPDUs are seen, I
was hoping there was some sort of active query that could be made
asking if there was anything weird and wireless nearby.....

> Regards,
> Bill Herrin
> --
> William Herrin ................ herrin at  bill at
> Owner, Dirtside Systems ......... Web: <>

More information about the NANOG mailing list