Reverse or inverse ARP from windows/linux - no way (!?!?)
in [Design]
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From: Boudewijn Dijkstra on 26 Mar 2010 11:52 Op Thu, 25 Mar 2010 22:54:42 +0100 schreef Didi <dp(a)tgi-sci.com>: > I tried today to figure out a simple way to give users of our > new netmca ( http://tgi-sci.com/tgi/nmcatb.htm ) to locate its > IP address once it gets one via dhcp when there is no internet > at the moment (when there is the device posts its IP to our domain > and customers can see it using a browser). > > Turned out there is nothing like an easy way to do that! Sending a UDP echo (port 7) to a broadcast address and subsequently receiving information about all of the connected netmca's, is not easy? A Java applet could do it. -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail)
From: D Yuniskis on 26 Mar 2010 13:07 Hi Dimiter, Didi wrote: > I tried today to figure out a simple way to give users of our > new netmca ( http://tgi-sci.com/tgi/nmcatb.htm ) to locate its > IP address once it gets one via dhcp when there is no internet > at the moment (when there is the device posts its IP to our domain > and customers can see it using a browser). OK, to be clear: - device uses DHCP to acquire an IP from server (somewhere); - user uses this IP to access web server within device; BUT - device has no way of conveying that IP to the user. Presumably, user's aren't smart enough to configure DHCP server to assign a *known* address to the device? BOOTPd is not available on the server (same issue)? Can your device register a name with a DynDNS service? Assuming you are dealing with Windows users, can you broadcast a name that folks could access? E.g., DimiterXXXX where XXXX is related to the device's MAC in some obvious way? (i.e., folks browse the network and then connect to the "obvious" host that shows up) Or, is my initial assumption incorrect? :<
From: markp on 26 Mar 2010 14:25 "Boudewijn Dijkstra" <sp4mtr4p.boudewijn(a)indes.com> wrote in message news:op.u96mc1k1j0diun(a)azrael.indes.com... > Op Thu, 25 Mar 2010 22:54:42 +0100 schreef Didi <dp(a)tgi-sci.com>: >> I tried today to figure out a simple way to give users of our >> new netmca ( http://tgi-sci.com/tgi/nmcatb.htm ) to locate its >> IP address once it gets one via dhcp when there is no internet >> at the moment (when there is the device posts its IP to our domain >> and customers can see it using a browser). >> >> Turned out there is nothing like an easy way to do that! > > Sending a UDP echo (port 7) to a broadcast address and subsequently > receiving information about all of the connected netmca's, is not easy? A > Java applet could do it. > That is what I was going to suggest. Just regularly send your aquired address via a UDP broadcast packet (say once a second), the bandwidth that would use is very low. There is another way, you can actually send arbitrary data in a DHCP_REQUEST packet. This could contain info about which device type is attempting to gain an address, and the server could log which addresses have been assigned to those types. No need for MAC lookups and the like. Mark
From: Didi on 26 Mar 2010 14:32 On Mar 26, 5:52 pm, "Boudewijn Dijkstra" <sp4mtr4p.boudew...(a)indes.com> wrote: > Op Thu, 25 Mar 2010 22:54:42 +0100 schreef Didi <d...(a)tgi-sci.com>: > > > I tried today to figure out a simple way to give users of our > > new netmca (http://tgi-sci.com/tgi/nmcatb.htm) to locate its > > IP address once it gets one via dhcp when there is no internet > > at the moment (when there is the device posts its IP to our domain > > and customers can see it using a browser). > > > Turned out there is nothing like an easy way to do that! > > Sending a UDP echo (port 7) to a broadcast address and subsequently > receiving information about all of the connected netmca's, is not easy? A > Java applet could do it. Well "easy" implies no necessity to program the alien system (windows). But I may look into the java option, I may have to do it this way. But I can see mass programming has gone higher level than practical. Clearly it is a hard thing to do for utility programmers, otherwise there would be some ARP variety tools out there. Dimiter
From: Didi on 26 Mar 2010 14:57
On Mar 26, 7:07 pm, D Yuniskis <not.going.to...(a)seen.com> wrote: > Hi Dimiter, > > Didi wrote: > > I tried today to figure out a simple way to give users of our > > new netmca (http://tgi-sci.com/tgi/nmcatb.htm) to locate its > > IP address once it gets one via dhcp when there is no internet > > at the moment (when there is the device posts its IP to our domain > > and customers can see it using a browser). > > OK, to be clear: > - device uses DHCP to acquire an IP from server (somewhere); > - user uses this IP to access web server within device; BUT > - device has no way of conveying that IP to the user. Yes, although usually a VNC server is accessed rather than a webserver. But there is a small webserver as well, part of the functionality is accessible via http. And yes, if there is no internet the device cannot access its (configurable) home domain to post its IP address there for user visibility and it has no other means to do that at the moment. > Presumably, user's aren't smart enough to configure DHCP > server to assign a *known* address to the device? It is not about them being smart enough, many of them just won't be bothered, have never dealt with that sort of thing etc. > BOOTPd is not available on the server (same issue)? > > Can your device register a name with a DynDNS service? > > Assuming you are dealing with Windows users, can you > broadcast a name that folks could access? E.g., > DimiterXXXX where XXXX is related to the device's > MAC in some obvious way? I could do some of these, sure. Have not implemented any dyndns so far, just the normal DNS thing I needed for the stack, but it can't be a lot. May be some way out. Although if it is not widely deployed I will still be facing the same issue on many locations. > (i.e., folks browse the network and then connect to > the "obvious" host that shows up) Well that's what I tried today at a customer and it worked. Without having a name for my netMCA; their network guy had installed there an "Angry IP scanner" (or similar name) which pinged the subnet in a loop and listed 6-7 responders; those with names were obvious (carried the names of people around the lab) and the two without the names were also obvious, one was the gateway and the other was the netmca. Even if not obvious if there are just a few hosts they can find out which is which by trial and error :-). So may be I don't have such a huge issue after all, I'll see how it works out over time before rushing into it. That's the strategy for now, at least, before someone screams over the phone "can't see the netmca"... Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/ |