RARP configuration Introduction Some network units (computers, terminals, ...) store their own config- uration on other machines. When these machines boot, they simply have no idea about their own IP number(s). They barely can communicate on the network because of this "lack" of identity. The RARP protocol is one of the few procotols (BOOTP and DHCP are other ones) which solves this dilemna. 11.. PPrriinncciippllee When a configuration-less device boots, it sends a broadcast using the RARP protocol (Reverse Address Resolution Protocol). Mostly, it says: Well, here I am. Here is a small message from me. From this message you should get my ethernet MAC address (6 hex digits uniquely identifying any ethernet adaptor ever built). From my MAC address, someone should be able to tell me my primary IP number. Thanks! One _L_i_n_u_x server may act as a RARP server. It will answer such a query only if it knows the answer. 22.. TTaasskk To define a RARP server, you must enter pairs of MAC address and IP number. You can also enter a host name (defined in /etc/hosts or in a DNS server). The kernel must be compiled with RARP support (either builtin or as a module). Linuxconf will inform you if your configuration is not suitable (no builtin, no module). 33.. DDiiaalloogg ffiieellddss Here are the four fields you have to fill for each RARP entries 33..11.. TThhiiss rreeccoorrdd iiss aaccttiivvee It is possible to comment out a record using this checkbox. Many RARP clients assume that if your server answer a RARP query, it may provide more boot services for this client. Diskless Linux workstation works this way. If your server do not provide such a service at one point in time, you are better to disable one entry. Note that several servers may process RARP queries on the same network without problem. 33..22.. HHoosstt nnaammee oorr IIPP nnuummbbeerr Enter here a host name either defined in /etc/hosts (See the menu "information about other hosts" in the Networking sub-menu of linuxconf) or in a DNS. Or just enter a plain IP number (x.y.z.w). 33..33.. EEtthheerrnneett aaddddrreessss ((TThhee MMAACC aaddddrreessss)) The MAC address is a long 6 hexadecimal number generally presented like this. 00:11:22:33:44:55 You can obtain this number different way. Here are some 33..33..11.. LLiinnuuxx ttaallkkss _L_i_n_u_x just print the MAC number when it boots. You can simply boot a linux configuration-less computer and watch it prints its MAC number. You will have plenty of time writing it down since it won't boot much further than that, until a RARP server respond to its query. Diskless nfsrooted linux workstation and X terminal come to mind as configuration-less linux device using (optionnally) RARP to identify itself. 33..33..22.. TThhee aaddaappttoorr ccoonnffiigguurraattiioonn pprrooggrraamm Most ethernet devices (all ?) come with a _D_O_S program allowing one to configure it. This program prints the MAC number. 33..33..33.. UUssee ttccppdduummpp One linux utility is called tcpdump. While it can _s_p_y the network and report about any packet which goes through, it is quite handy to pick those "annoying to type" MAC numbers. Just execute tcpdump rarp Boot the device and watch it there. Cut and paste the number in linuxconf's dialog, add a name or an IP number and let linuxconf activates the configuration. Watch the device completing its boot process successfully. Automate this mecanism is on the TODO list of linuxconf. 33..44.. CCoommmmeenntt Put whatever you want here. Maybe just a reminder of the reason why you disabled the entry.