--- name: "guessnet" section: "1" platform: "linux" package: "guessnet" version: "0.14-1" release: "Debian 3.0 (Woody)" platforms: ["linux"] url: "https://new.carta.tech/guessnet" --- # guessnet(1) guess the current network location using fake ARP requests. ## NAME guessnet - guess the current network location using fake ARP requests. ## SYNOPSIS **guessnet** \[*options*\] \[*ethernet\_interface*\] \[*config\_file*\]\ ## DESCRIPTION **Guessnet** is a program to guess the current network location using fake ARP packets. The program expects a list of network data, that can be read from **config\_file** or from standard input, and prints a tag identifying the network it finds connected to the specified **ethernet\_interface** on standard output. Every line of network data describes a network candidate and its relative tag. A default tag is printed if no candidate is detected, and can be specified with the **-d** or **--default** commandline options. The program decides that no networks are found after some seconds passed without receiving suitable ARP replies. The timeout can be changed with the **-t** or **--timeout** commandline option. Some hardware needs longer timeouts to compensate for long initialization times of the network card. If **ethernet\_interface** is omitted, \`eth0' is assumed. ## OPTIONS These programs follow the usual GNU command line syntax, with long options starting with two dashes (\`-'). - **-d, --default=STRING** Tag to print if no known networks are found. Defaults to **ethernet\_interface**-none. - **-t, --timeout=INT** Timeout in seconds used to wait for response packets (defaults to 3). - **--init-time=INT** Time (in seconds) to wait for the interface to initialize when it is not found already up at program startup (defaults to 3 seconds) - **-v, --verbose** Operate verbosely. - **-V, --very-verbose** Operate more verbosely, for debugging purposes. - **--version** Show version of program. - **--usage** Show a brief usage message. - **-?, --help** Show summary of options. ## NETWORK DATA FORMAT The network data looks like this: ``` # Empty lines and comment lines starting with '#' # are ignored. # Home network 192.168.1.2 00:01:02:03:04:05 192.168.1.1 home # University 130.136.3.42 05:06:03:02:01:0A 130.136.1.1 university 130.136.3.42 15:13:B3:A2:2F:CD 130.136.1.2 university # Work 10.1.1.42 0A:0B:0C:0D:0E:0F 10.1.1.1 work 10.1.1.42 0F:0E:0D:0C:0B:0A 10.1.1.2 work ``` A network data line identifies a candidate network to test and contains 4 fields: - **Local IP** Indicates the IP to use as a source IP address for ARP requests. At the moment I lack documentation about the ARP protocol, but I would like to remove the need to specify this field. It should, however, be a valid (and probably unused) IP address inside the network we are testing. - **Remote MAC** Indicates a MAC address for a host we know is present in this network. You can find macaddresses of other computers in the network using the command 'arp -v'; see man [arp(8)](/arp/8.md) for more details. - **Remote IP** Indicates the IP address corresponding to the MAC address given. - **Network name** Name to be printed on standard output if this network is found. ## NOTES Here follow some notes to give suggestions and examples on **guessnet** usage. ## /etc/network/interfaces integration **guessnet** gets interesting if combined with the standard debian ifupdown scripts, to automatically guess what data to use to configure the interface. Here's an example of an interfaces file using **guessnet**: ``` auto lo eth0 iface lo inet loopback mapping eth0 # Too bad there's no way to pass commandline options to script script /usr/bin/guessnet # Test for my other home PC map 192.168.1.2 00:01:02:03:04:05 192.168.1.1 eth0-home # Test for the gateway we have at work map 10.1.1.42 00:0A:0B:0C:0D:0E 10.1.1.1 eth0-work # Home network configuration iface eth0-home inet static address 192.168.1.2 netmask 255.255.255.0 broadcast 192.168.1.255 gateway 192.168.1.1 up ln -fs /etc/roaming/resolv.conf_home /etc/resolv.conf up echo "smarthost: main.home" > /etc/roaming/exim_options up rm -f /etc/roaming/not_online # Work network configuration iface eth0-work inet static address 10.1.1.42 netmask 255.255.255.0 broadcast 10.1.1.255 gateway 10.1.1.1 up ln -fs /etc/roaming/resolv.conf_work /etc/resolv.conf up echo "smarthost: mail.work.it" > /etc/roaming/exim_options up rm -f /etc/roaming/not_online # eth0 defaults (too bad there's no 'disabled' method for iface...) iface eth0-none inet static address 192.168.1.2 netmask 255.255.255.0 up ln -fs /etc/roaming/resolv.conf_none /etc/resolv.conf up touch /etc/roaming/not_online ``` ## Getting remote host macaddresses When you prepare the input data to **guessnet** you may need to know the MACaddress of a remote interface in the local network. There are many ways to do this: the easier is by using the **arping** utility by issuing "**arping** **\[hostname\]**". If you haven't **arping** installed in your system, issue the command "**arp -a \[hostname\]**" to display the MAC address taking the information from the ARP cache of your machine. You might want to ping the remote interface first to be sure to have the informations in the cache. ## SEE ALSO [**ifup**(8)](/ifup/8.md), [**interfaces**(5)](/interfaces/5.md), [**arping**(8)](/arping/8.md). ## AUTHOR **guessnet** has been written by Enrico Zini \, taking the ARP network detection code from laptop-netconf by Matt Kern \, based in turn on divine by Felix von Leitner \.