Find IP address of directly connected device

Question

Is there a way to find out the IP address of a device that is directly connected to a specific ethernet interface  I e  given one host  one wired ethernet connection and one second host connected to this wired connection  which layer or protocol below IP could be used to find this out   I would also be comfortable with a Windows-only solution using some Windows-API function or callback    I know that the real way to do this would probably via DHCP  but this is about discovering a legacy device

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Windows 7 has the arp command within it   arp -a should show you the static and dynamic type interfaces connected to your system

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To use DHCP  you d have to run a DHCP server on the primary and a client on the secondary  the primary could then query the server to find out what address it handed out   Probably overkill   I can t help you with Windows directly   On Unix  the  arp  command will tell you what IP addresses are known to be attached to the local ethernet segment   Windows will have this same information  since it s a core part of the IP Ethernet interface  but I don t know how you get at it   Of course  the networking stack will only know about the other host if it has previously seen traffic from it   You may have to first send a broadcast packet on the interface to elicit some sort of response and thus populate the local ARP table

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Mmh     there are many ways  I answer another network discovery question  and I write a little getting started   Some tcpip stacks reply to icmp broadcasts  So you can try a PING to your network broadcast address   For example  you have ip 192 168 1 1 and subnet 255 255 255 0   ping 192 168 1 255 stop the ping after 5 seconds watch the devices replies   arp -a   Note   on step 3  you get the lists of the MAC-to-IP cached entries  so there are also the hosts in your subnet you exchange data to in the last minutes  even if they don t reply to icmp get   Note  2    now I am on linux  I am not sure  but it can be windows doesn t reply to icm get via broadcast   Is it the only one device attached to your pc   Is it a router or another simple pc

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Your Best Approach is to install Wireshark  reboot the device wait for the TCP UDP stream    broadcasts will announce the IP address for both Ethernet ports This is especially useful when the device connected does not have DHCP Client enabled  then you can go from there

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You can also get information from directly connected networking devices  such as network switches with LDWin  a portable and free Windows program published on github   http   www sysadmit com 2016 11 windows-como-saber-la-ip-del-switch-al-que-estoy-conectado html  LDWin supports the following methods of link discovery  CDP  Cisco Discovery Protocol  and LLDP  Link Layer Discovery Protocol    You can obtain the model  management IP  VLAN identifier  Port identifier  firmware version  etc

[windows] Find IP address of directly connected device

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