Reverse or inverse ARP from windows/linux - no way (!?!?)
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From: glen herrmannsfeldt on 29 Mar 2010 11:16 In comp.protocols.tcp-ip Didi <dp(a)tgi-sci.com> wrote: > On Mar 29, 7:37?am, "JosephKK"<quiettechb...(a)yahoo.com> wrote: (snip) >> APR lower level than UDP? ?I don't think so. ?Same >> level at best, below UDP is MAC and PHY only. > Uhm, not so sure. Same level as UDP in that they both have the > Ethernet protocol type set to "internet", perhaps; but the > data inside a UDP packet are encapsulated into that level, > whereas the ARP data are purely Ethernet encapsulated. > This should put it one level lower - at least unofficially? MAC at layer 2 (ethernet switch level), IP at layer 3, TCP and UDP at layer 4. Sometimes I think that ICMP should be layer 4 (as in ping), other times in layer 3. It does go inside an IP packet. ARP does not have the IP (X'0800') ethernet type, so it seems that it should also be layer 3. -- glen
From: Boudewijn Dijkstra on 29 Mar 2010 11:32 Op Mon, 29 Mar 2010 17:10:34 +0200 schreef glen herrmannsfeldt <gah(a)ugcs.caltech.edu>: > In comp.protocols.tcp-ip markp <map.nospam(a)f2s.com> wrote: > (snip, someone wrote) > > Some will respond to a ping to the broadcast address, others not. Some will even respond differently to the subnet broadcast address (e.g. 192.168.0.255) than the global broadcast address (255.255.255.255). -- Gemaakt met Opera's revolutionaire e-mailprogramma: http://www.opera.com/mail/ (remove the obvious prefix to reply by mail)
From: Didi on 29 Mar 2010 12:31 On Mar 29, 6:32 pm, "Boudewijn Dijkstra" <sp4mtr4p.boudew...(a)indes.com> wrote: > Op Mon, 29 Mar 2010 17:10:34 +0200 schreef glen herrmannsfeldt > <g...(a)ugcs.caltech.edu>: > > > In comp.protocols.tcp-ip markp <map.nos...(a)f2s.com> wrote: > > (snip, someone wrote) > > > Some will respond to a ping to the broadcast address, others not. > > Some will even respond differently to the subnet broadcast address (e.g. > 192.168.0.255) than the global broadcast address (255.255.255.255). > Hmm, do you still think it is "simple" (just kidding :-)). The necessity to poll, ping the entire subnet etc. nonsense summarizes what todays PC programming has become. Instead of simply sending a single packet to a known destination and use the single packet reply, why not send a few hundred or, better, a few thousand of them (the latter is the case when we would really need it to work, of course :-) ), then sift through the replies... Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
From: Andrew Smallshaw on 29 Mar 2010 12:35 On 2010-03-25, Didi <dp(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). CDP comes to mind as one option with allows any connected device to advertise its identity and IP address on the local subnet. I'm aware that it has at least in theory been superceded by LLDP but I have no experience of that, and CDP is very simple whereas LLDP _may_ be more complex. It's primarily a Cisco protocol but it is documented and clients and viewers are available for Unix and Windows machines. -- Andrew Smallshaw andrews(a)sdf.lonestar.org
From: markp on 29 Mar 2010 12:59
"Didi" <dp(a)tgi-sci.com> wrote in message news:851c373c-9078-4880-aca1-18fb3e83389e(a)g19g2000yqe.googlegroups.com... On Mar 29, 6:32 pm, "Boudewijn Dijkstra" <sp4mtr4p.boudew...(a)indes.com> wrote: > Op Mon, 29 Mar 2010 17:10:34 +0200 schreef glen herrmannsfeldt > <g...(a)ugcs.caltech.edu>: >> >> In comp.protocols.tcp-ip markp <map.nos...(a)f2s.com> wrote: >> (snip, someone wrote) >> >> Some will respond to a ping to the broadcast address, others not. >> >> Some will even respond differently to the subnet broadcast address (e.g. >> 192.168.0.255) than the global broadcast address (255.255.255.255). >> > Hmm, do you still think it is "simple" (just kidding :-)). :-) OK, the ARP way sounds like you've got to send a ping first to establish the route. However, since the only things you are worried about are your web-servers you can guarantee they respond to that as you would have programmed them too. As an aside, wouldn't the DHCP server when allocating addresses in the first place do that automatically? The original idea of sending a UDP broadcast enquiry packet and getting replies is quite simple though. Only your servers would reply, and you could even send the desired server's MAC address in the enquiry packet so only one device that matches it would respond. Mark. |