Reverse or inverse ARP from windows/linux - no way (!?!?)
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From: Albert Manfredi on 1 Apr 2010 15:57 On Mar 29, 5:19 am, Didi <d...(a)tgi-sci.com> wrote: > 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? I totally agree with you that ARP and UDP are in different protocol layers, but your response here is confusing. ARP uses a Type of 0x806, whereas IPv4 uses 0x0800. See: http://www.iana.org/assignments/ethernet-numbers So, ARP frames are only encapsulated by the Ethernet frame, nothing more. Whereas UDP datagrams are encapsulated inside an IP datagram, which in turn is inside the Ethernet frame. Bert
From: glen herrmannsfeldt on 1 Apr 2010 16:50 In comp.protocols.tcp-ip Albert Manfredi <bert22306(a)hotmail.com> wrote: (snip) > I totally agree with you that ARP and UDP are in different protocol > layers, but your response here is confusing. > ARP uses a Type of 0x806, whereas IPv4 uses 0x0800. See: > http://www.iana.org/assignments/ethernet-numbers > So, ARP frames are only encapsulated by the Ethernet frame, nothing > more. Whereas UDP datagrams are encapsulated inside an IP datagram, > which in turn is inside the Ethernet frame. Counting that way, why not any of the higher layers? Back to ICMP for a moment. As ICMP is also carried in an IP frame, it seems that it should be the same layer as TCP and UDP. In terms of ping, that makes sense. In terms of route redirect or source quench, it doesn't. In the latter case, the ICMP are to help the IP layer and not much about anything higher. ARP is there to help IP send frames on networks where layer 2 needs such help. -- glen
From: Albert Manfredi on 1 Apr 2010 18:56 On Apr 1, 4:50 pm, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote: > > I totally agree with you that ARP and UDP are in different protocol > > layers, but your response here is confusing. > > ARP uses a Type of 0x806, whereas IPv4 uses 0x0800. See: > >http://www.iana.org/assignments/ethernet-numbers > > So, ARP frames are only encapsulated by the Ethernet frame, nothing > > more. Whereas UDP datagrams are encapsulated inside an IP datagram, > > which in turn is inside the Ethernet frame. > > Counting that way, why not any of the higher layers? > > Back to ICMP for a moment. As ICMP is also carried in > an IP frame, it seems that it should be the same layer as TCP > and UDP. In terms of ping, that makes sense. In terms of > route redirect or source quench, it doesn't. In the latter > case, the ICMP are to help the IP layer and not much about > anything higher. ICMP is at the same layer as UDP, TCP, or IGMP, for that matter. But neither ICMP nor IGMP are meant to provide the general purpose "transport layer" services that TCP and UDP provide. I'd classify ICMP and IGMP as special purpose protocols to control or monitor layer 3 devices. > ARP is there to help IP send frames on networks where > layer 2 needs such help. True. ARP is network-agnostic. It happens to have been used in IP nets most often, but that does not mean that it can ONLY be used to resolve IP addresses to physical addresses. It could in principle have been used for DECnet or any of those other forgotten protocols. Bert
From: glen herrmannsfeldt on 1 Apr 2010 19:04 In comp.protocols.tcp-ip Albert Manfredi <bert22306(a)hotmail.com> wrote: (snip) > True. ARP is network-agnostic. It happens to have been used in IP nets > most often, but that does not mean that it can ONLY be used to resolve > IP addresses to physical addresses. It could in principle have been > used for DECnet or any of those other forgotten protocols. Make that should have been used for DECnet. As I remember, DECnet changes the MAC address based on the DECnet address, such that no ARP is needed. You can only do that for one protocol per interface, though. There was not so long ago on another newsgroup someone who had a system that uses DHCP to assign the IP address, then brings up DECnet. Somehow the change of MAC address confused other parts of the system. Then Appletalk has AARP instead of using ARP. I don't know IPX very well, so I don't know what it does. -- glen
From: JosephKK on 2 Apr 2010 00:14
On Wed, 31 Mar 2010 21:09:46 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Wed, 31 Mar 2010 00:31:23 +0200, Hans-Bernhard Bröker <HBBroeker(a)t-online.de> wrote: > >>Didi wrote: >>> 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". > >This erroneous statement alone shows that you are ill prepared to participate >in this discussion. If you think UDP "sits" on top of IP you are very mistaken. >It is a parallel (at the same level) link/transport protocol. Arrghkk, gllujk, orwrrpp. (translation ankle tastes soo good) > >Moreover, you desired email reply shows arrogant disregard for USENET norms. This still stands. >> >> > There are DHCP servers in the absence of internet. >> >>That's only true for a meaning of the term "internet" that IMHO rather >>strictly contradicts with your self-proclaimed expertise in internet >>technologies. What exactly did the 'I' in IP mean again? >> ><Snip> |