Reverse or inverse ARP from windows/linux - no way (!?!?)
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From: Didi on 4 Apr 2010 06:13 On Apr 4, 10:55 am, gopher <shuswapren...(a)shaw.ca> wrote: > On Mar 25, 2:54 pm, Didi <d...(a)tgi-sci.com> 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). > > > Turned out there is nothing like an easy way to do that! > > > There are some utilities which can be used to ping the entire subnet; > > then list the arp cache, locate the known MAC address and > > see its IP. But these are far from something one would want to ask > > customers to deal with, long lists, necessity to search etc. , heck, > > it > > will generate more calls to me than if I do it for them every time. > > > In an attempt to solve it I spent 10 minutes adding RARP reply > > to our device Ethernet related stuff - so it would reply to an ARP > > inquiry #3 by sending its IP address (it only has one); and then spent > > perhaps 3 hours googling, moogling, you name it, searching for some > > piece of code to do that at the wintel side. Even rebooted the wintel > > laptop to ubuntu to try it out from there (thought arp -r or something > > would just work), oh no. No way. Spent perhaps half an hour of > > moogling for linux rarp, same thing. > > > How on Earth is that possible?! I can understand how many things > > are retarded as one would expect them to be on a x86 based thing, > > but this is too simple even for the x86 world. > > > Any ideas? I have not faced the issue in real life yet (users tend > > to have internet) but this is bound to happen and I am looking for > > some solution. > > > Dimiter > > > ------------------------------------------------------ > > Dimiter Popoff Transgalactic Instruments > > >http://www.tgi-sci.com > > ------------------------------------------------------http://www.flickr..com/photos/didi_tgi/sets/72157600228621276/ > > keep in mind, if your "interesting mac" address host is using dhcp to > get it's IP address, and your DHCP server which it uses is on the > other side of your broken Internet circuit, using inverse-arp would be > a very temporary solution. DHCP based IP addresses are given out with > a lease time that expires. The host should clear it's IP address if > the lease time expires. Lease times can be from minutes to days. I've > often seen 24hrs, but I've seen as low as 1 hour. The DHCP client host > will try to renew at the leases half-life (and probably again after > that until the lease expires, I'll have to look that up one day. I'd > guess it would try half way between the failed renewal and the > expirey, and keep doing that til the expirey, but it's just a guess) > > Glen#2 I have made it to issue a new DHCP request some time before it expires, just had a look at it - 3 minutes before expiration. Works so far, but I don't have many systems deployed yet. Anyway, I have put this(and other similar high-level behaviour) in a DPS script for a reason, so it can easily be changed it if needed :-) . BTW I think I posted the reason why there is no rarp/inarp utility under windows (their API won't allow it, a guy responded elsewhere). The same guy said he had written one himself for linux, so it seems to be possible there - but I did not locate anything readily available in a half an hours search. Dimiter
From: David Schwartz on 4 Apr 2010 06:26 On Mar 31, 2:43 am, "markp" <map.nos...(a)f2s.com> wrote: > For this thread to make any sense you should be able to define exactly what > an 'Internet' is. Off you go... I certainly can define exactly what the "Internet" is, but I don't see how it's relevant. DS
From: krw on 4 Apr 2010 11:58
On Wed, 31 Mar 2010 10:43:34 +0100, "markp" <map.nospam(a)f2s.com> wrote: > >"David Schwartz" <davids(a)webmaster.com> wrote in message >news:8a306499-3f14-43cd-9999-a0349dce0ad8(a)u22g2000yqf.googlegroups.com... >On Mar 29, 3:44 pm, Hans-Bernhard Br�ker <HBBroe...(a)t-online.de> >wrote: > >>> I believe that, strictly speaking, that can't happen. If you have no >>> internet at the moment, you don't have DHCP either. Remember that DHCP >>> itself is a UDP service. UDP in turn works on top of IP, and that, for >>> better or for worse, is "internet". > >>Many networks that have nothing whatsoever to do with the Internet >>have adopted its protocol. You can't have the Internet without IP, but >>you can certainly have IP with the Internet. > >For this thread to make any sense you should be able to define exactly what >an 'Internet' is. Off you go... There is only one Internet, so "an Internet" is grammatically incorrect. It should be "the Internet". There is no argument about the definition of "Internet", as there is only one (note that the capitalized "Internet" denotes a proper noun). If you're not talking about *the* Internet, rather a network of computers outside *the* Internet, you should say "an internet". There you might have an legitimate argument over the precise definition of "internet". |