Re: reliably detecting the presence of a bridge?

On Wed, Dec 16, 2015 at 4:36 AM, Dave Taht wrote: > On Tue, Dec 15, 2015 at 4:19 PM, William Herrin wrote: >> 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

Re: reliably detecting the presence of a bridge?

On 12/19/2015 12:17, William Herrin wrote: [snip] I recommend you stop using the word "bridge." I think see where you're heading with it, but I think you're chasing a blind alley which encourages a false mental model of how layer 2 networks function. You came here for answers. This is one of

Re: reliably detecting the presence of a bridge?

In the end, there seems to be no "reliable" way to ask the network my question. But... WOW! Thank you all for your interesting and clever techniques!

Re: reliably detecting the presence of a bridge?

>I think I have used WiFi terminals ("air ports", "WiFi routers" [spit]) >that offer a "bridge" mode, apparently to build a dedicated radio link >between two such terminals. The ones I've seen Normally those things are routers, typically with NAT on the wifi side. If you put it in bridge

Re: reliably detecting the presence of a bridge?

On 12/19/2015 16:53, James R Cutler wrote: [snip] But I still have one question (which might be based on errors)-- I think I have used WiFi terminals ("air ports", "WiFi routers" [spit]) that offer a "bridge" mode, apparently to build a dedicated radio link between two such terminals. Are

Re: reliably detecting the presence of a bridge?

On 12/19/2015 17:15, Larry Sheldon wrote: On 12/19/2015 16:53, James R Cutler wrote: [snip] But I still have one question (which might be based on errors)-- I think I have used WiFi terminals ("air ports", "WiFi routers" [spit]) that offer a "bridge" mode, apparently to build a dedicated

Re: reliably detecting the presence of a bridge?

> On Dec 19, 2015, at 4:53 PM, Larry Sheldon wrote: > > On 12/19/2015 12:17, William Herrin wrote: > > [snip] > >> I recommend you stop using the word "bridge." I think see where you're >> heading with it, but I think you're chasing a blind alley which >> encourages a

RE: reliably detecting the presence of a bridge?

-Original Message- From: NANOG [mailto:nanog-boun...@nanog.org] On Behalf Of Dave Taht Sent: Wednesday, December 16, 2015 4:37 AM To: William Herrin <b...@herrin.us> Cc: NANOG <nanog@nanog.org> Subject: Re: reliably detecting the presence of a bridge? The latter. In this ca

Re: reliably detecting the presence of a bridge?

[Dave asked me to repost this to the list -- not sure how useful this little lead is; haven't worked on this for more than half a decade.] I don't have a good platform to test this on today, but one way to detect a wireless bridge a couple of years ago was to send a SNAP packet (actually anything

Re: reliably detecting the presence of a bridge?

If LLDP (link layer discovery protocol) is enabled, you could try using that. There is a system capabilities TLV in the LLDPDU sent by a system, but I'm not sure how reliably it is filled in, especially if a device is capable of both switching and routing. The way LLDP is supposed to work is a

Re: reliably detecting the presence of a bridge?

On Tue, Dec 15, 2015 at 4:19 PM, William Herrin wrote: > On Tue, Dec 15, 2015 at 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 >>

Re: reliably detecting the presence of a bridge?

On Tue, 15 Dec 2015, 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

Re: reliably detecting the presence of a bridge?

Dave Taht wrote: > 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 > bridge. Listen to spanning tree protocol. Masataka Ohta

reliably detecting the presence of a bridge?

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

Re: reliably detecting the presence of a bridge?

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

Re: reliably detecting the presence of a bridge?

On Tue, Dec 15, 2015 at 10:48:50AM +0100, 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 >

Re: reliably detecting the presence of a bridge?

Why do you care if there's a bridge? Seems you care about higher latency, packet loss, lower reliability, etc. Measure what matters and act on that, rather than trying to guess performance from link type. Matthew Kaufman (Sent from my iPhone) > On Dec 15, 2015, at 5:48 AM, Dave Taht

Re: reliably detecting the presence of a bridge?

On Tue, Dec 15, 2015 at 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? Hi Dave, Start with precision