Reverse or inverse ARP from windows/linux - no way (!?!?)
in [Design]
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From: Didi on 29 Mar 2010 22:22 On Mar 30, 1:44 am, Hans-Bernhard Bröker <HBBroe...(a)t-online.de> wrote: > 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 > > 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". Oh no. Here we go again. I got quite a few really insightful replies and now this. There are DHCP servers in the absence of internet. For example, a popular type of cable models do assign IP addresses of the 192.168.... kind when it has no link over the TV cable. Routers do that whether they are linked to the internet or not. On which planet do you live. > > > Turned out there is nothing like an easy way to do that! > > Well, the problem is nowhere near as easy as it appears at first sight. > It's called a "network" because it's _work_ to set up a properly > functioning net. Thank for the opinion. But you are posting to groups where some minimal understanding of how things work is implied, these are not general talk forums. Have a look at the thread in its entity and you will see what I mean. No offense meant, just being practical and trying to save time to myself and the rest of the people who really had something to say. > > > How on Earth is that possible?! > > You'll want to look up "zero config networking". That's what the big > guys came up with to address this very same issue. You'll see Apple > mentioned rather a lot, for their "Rendezvouz"/"Bonjour" project. No. I was quite particular explaining what I wanted, the fact that you did not understand it should have indicated to you that you are about to post to a thread you do not understand. > > And let me point out I'm completely flabbergasted that nobody mentioned > this before me --- not over here in c.a.embedded, anyway. I mean, come > on guys: not a single owner of an Apple Airport base station speaking > up, wondering what all these people keep talking about for days, when a > "normal" WLAN box just does the job??? Same answer. The fact that you did not understand what we were talking about should have been sufficient for you to grasp that the topic is outside of your competence and that you have nothing to contribute. These are technical newsgroups. Dimiter
From: JosephKK on 30 Mar 2010 00:07 On Mon, 29 Mar 2010 15:16:49 +0000 (UTC), glen herrmannsfeldt <gah(a)ugcs.caltech.edu> wrote: >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 First off the TCP/IP stack is 4 levels, and the ISO model is 7 layers. Thus there is intrinsic mismatch. Much of the TCP/IP model tools span two or more layers in the ISO model. The real deal for TCP/IP protocol definitions comes from the IETF RFC library. http://www.ietf.org/rfc.html Please note that this RFC information is freely available for any use. Wikipedia tries to allocate levels but fails sometimes: http://en.wikipedia.org/wiki/OSI_model http://en.wikipedia.org/wiki/TCP/IP_model And another opinion: http://mike.passwall.com/networking/netmodels/isoosi7layermodel.html Personally i place IP and UDP at the ISO link layer and ISO the transport layer. After all they are sending the message. (R)ARP is about different network functions and talks to the same layer (going towards Phy) as TCP and IP; however it functions in link, transport, and network ISO layers. So where do you want to place it?
From: JosephKK on 30 Mar 2010 00:15 On Tue, 30 Mar 2010 00:44:16 +0200, Hans-Bernhard Bröker <HBBroeker(a)t-online.de> wrote: >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 > >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". No. UDP does not use IP all. It operates in parallel with IP, and provides a different service. Al least that is what the RFCs say. > >> Turned out there is nothing like an easy way to do that! > >Well, the problem is nowhere near as easy as it appears at first sight. > It's called a "network" because it's _work_ to set up a properly >functioning net. > >> How on Earth is that possible?! > >You'll want to look up "zero config networking". That's what the big >guys came up with to address this very same issue. You'll see Apple >mentioned rather a lot, for their "Rendezvouz"/"Bonjour" project. > >And let me point out I'm completely flabbergasted that nobody mentioned >this before me --- not over here in c.a.embedded, anyway. I mean, come >on guys: not a single owner of an Apple Airport base station speaking >up, wondering what all these people keep talking about for days, when a >"normal" WLAN box just does the job???
From: robertwessel2 on 30 Mar 2010 00:59 On Mar 29, 11:15 pm, "JosephKK"<quiettechb...(a)yahoo.com> wrote: > On Tue, 30 Mar 2010 00:44:16 +0200, Hans-Bernhard Bröker <HBBroe...(a)t-online.de> wrote: > >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 > > >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". > > No. UDP does not use IP all. It operates in parallel with IP, and provides > a different service. Al least that is what the RFCs say. UDP (and TCP) both use IP as their lower layer. UDP operate in parallel with *TCP* and provides a different service. They *both* run over IP. It is most emphatically *not* what the RFCs say. In fact, the opening paragraph of RFC786 (which defines UDP) is: "This User Datagram Protocol (UDP) is defined to make available a datagram mode of packet-switched computer communication in the environment of an interconnected set of computer networks. This protocol assumes that the Internet Protocol (IP) [1] is used as the underlying protocol." And the prior poster is correct - it's IP that basically defines the Internet - the whole Internet exists to move IP packets around, and protocols like ICMP, UDP and TCP are built on top of IP. A number of other less common protocols also are built directly on top of IP (rather than on top of UDP or TCP). For example, the communication between routers running OSPF happens over IP, but uses protocol #89, which is distinct from TCP (6), UDP (17) and ICMP (1). As for DHCP, it does, in fact, use a UDP packet, although in many implementations that's more a formality and the IP header is largely faked during initial system startup. Having it an actual UDP packet makes it rather easier for the (DHCP) servers and the rest of the network, though.
From: Dave Platt on 30 Mar 2010 01:21
In article <0iu2r55qbfhts94ferln64q15efn0pb4km(a)4ax.com>, JosephKK <quiettechblue(a)yahoo.com> wrote: >No. UDP does not use IP all. It operates in parallel with IP, and provides >a different service. Al least that is what the RFCs say. You are mistaken on this point. UDP is built on top of IP. TCP is built on top of IP. ICMP is built on top of IP. These three protocols are peers, at the same level in the network stack. -- Dave Platt <dplatt(a)radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |