Reverse or inverse ARP from windows/linux - no way (!?!?)
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From: glen herrmannsfeldt on 26 Mar 2010 02:32 In comp.protocols.tcp-ip Didi <dp(a)tgi-sci.com> wrote: (snip) > Yes. And this works fine if the customer has internet, but I know > I won't be lucky all the time...(so far so good, though :-) ). Internet or not, most have DHCP, but not all. Many will want any such devices statically addressed. If the device has non-volatile memory (usually flash) then it can store its IP address. DHCP came when diskless machines had no non-volatile memory other than factory configured ROMs. (One with the ethernet MAC address in them, another with the boot code. If not, then you can require DHCP. Many DHCP servers allow one to configure static assignments based on ethernet MAC address. If the DHCP server has a log file, then it is easy to find the recently assigned address. Otherwise, a ping to the broadcast address for the subnet will find some, but not all, devices. (They will get ARP entries if they reply to the ping.) If the device has an LCD or other display, then you can have a way to find the IP address through the display, and configure any stored addresses. -- glen
From: Didi on 26 Mar 2010 03:14 On Mar 26, 8:32 am, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote: > In comp.protocols.tcp-ip Didi <d...(a)tgi-sci.com> wrote: > (snip) > > > Yes. And this works fine if the customer has internet, but I know > > I won't be lucky all the time...(so far so good, though :-) ). > > Internet or not, most have DHCP, but not all. Many will want > any such devices statically addressed. Well yes, but the default state as I ship it is with dhcp on (attempted) and if it times out fallback to a (re)programmable fixed IP address. Once they gain VNC access to the device they can switch dhcp off etc. from a menu and set a static address, I have no issues with that case. > If the device has non-volatile memory (usually flash) then > it can store its IP address. DHCP came when diskless machines > had no non-volatile memory other than factory configured ROMs. I know, but this was quite some time ago :-). Now this device ships with a HDD inside, has an EEPROM, runs a fullblown DPS and "only" needs tcp/ip access to have a monitor, keyboard and mouse. In fact I also offer it without a HDD - the whole DPS + application software fits in a 2M ROM (most of it being a ROM "disk"), flash actually. To repost the link to the device page, http://tgi-sci.com/tgi/nmcatb.htm . > If not, then you can require DHCP. Many DHCP servers allow one > to configure static assignments based on ethernet MAC address. I recently had such an encounter. Wanted to be able to remotely access the device behind a router and asked the network people on that site to forward the port of interest. They said it would take a static IP to do that; I reconsidered and made the device initiate the connection to my support VNC client which now I run in passive (listening) mode. Just made the device attempt it every 20 seconds or so - the user being able to turn that on/off. > If the device has an LCD or other display, then you can have a > way to find the IP address through the display, and configure > any stored addresses. Well if it had such a display it could just display its IP address :-). But it has not and technically there is no need for one. Just a tiny windows utility which will send a RARP inquiry to a MAC address and list the result would do in an internet-less environment; a browser is enough already if there is internet. Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/ Original message: http://groups.google.com/group/comp.arch.embedded/msg/424b95a94a446059?dmode=source
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 |