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arp interview questions

Top arp frequently asked interview questions

How to query IPv6 NDP (neighbor discovery protocol) table for a specific neighbor

I am using Linux and trying to figure out how to query (via an API) the NDP table for a specific entry. The only example I have found so far (in the source for iproute2) uses Netlink and gets the entire table. Is there a way to query Netlink for a specific IPv6 addr on a specific interface? Or is there a different way than using Netlink that I should be going about doing it?


Source: (StackOverflow)

Is there any better way to get mac address from arp table?

I want to get a mac address from arp table by using ip address. Currently I am using this command

arp -a $ipAddress | awk '{print $4}'

This command prints what I want. But I am not comfortable with it and I wonder if there is any built-in way or more stable way to do this.


Source: (StackOverflow)

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Get a remote MAC adress via IPv6

Hey guys, i searched the web for a solution, but i found nothing! :(

Is it possible to get the MAC from an another PC in the same Network via IPv6 (without WMI)? With IPv4 it is easy (ARP). IPv6 uses the "Neighbor Discovery Protocol" (NDP) to get the MAC adress. Are there any methods in .Net for this?

Any suggestions? Thanks for your help!

Regards

Fabian


Source: (StackOverflow)

Send a ping to each IP on a subnet

Is there a command line based way to send pings to each computer in a subnet? Like

for(int i = 1; i < 254; i++)
    ping(192.168.1.i);

to enforce arp resolution?


Source: (StackOverflow)

How do I access ARP-protocol information through .NET?

I am trying to figure out what devices are online and offline in our LAN. I've seen many programs doing a kind of graphical network overview, presenting LAN IP and MAC addresses. I would like to know if and how those (ARP?) information can be pulled from C#/.NET ?

Any sample code snippets/links would be appreciated.


Source: (StackOverflow)

How do I query the ARP table on iPhone?

I am new on iPhone development, and I want to integrate wake-on-lan into my application without squeezing my users to enter the computers MAC address when the IP is already known. I googled for about some hours, took the source code of an ARP tool, but I don't know how to manage this on iPhone.


Source: (StackOverflow)

Is there a way to send ARP request via Java?

Is there a way to send ARP request within a Java application? I know that ARP is sitting a layer under TCP and UDP therefore by default Java couldn't send ARP request. I am just wondering is there any 3rd party Java library that will allow you to send ARP request.

To capture ARP reply, I know I can use jpcap so that part is solved.

Thanks


Source: (StackOverflow)

resolving mac address for IP

I need to generate ethernet header that includes destination mac address, (since libnfnetlink gives only ip header before prerouting takes place), the outgoing interface # is also known so the lookup can be made in correct network.

What's the library/function to resolve MAC from IP?


Source: (StackOverflow)

Why arp ignore/annouce are not enable by default [closed]

I have a specific question which need experience for an answer:

Why arp_ignore / arp_announce are not enable by default on linux installation (debian for example) is there a specific reason ?

Which interest to receive arp answer from wrong network interfaces ?

Thanks for your help.

Regards,


Source: (StackOverflow)

Stopping ARP protocol in window

Is there a way to stop ARP protocol in window , i have developed my own ARP protocol which add authentication to ARP using a java api called jnetpcap. but , still haven't found a way to stop the normal ARP. now i am deleting the ARP entry updated from the normal arp request protocol but still i need to stop my machine from sending reply to those request.


Source: (StackOverflow)

How to get the IP address of a remote host from its Ethernet address?

I'm looking for some Linux code to find an IP address from an Ethernet address. I suppose I have to do some inverse ARP trickery but I don't find any example...


Source: (StackOverflow)

How do I send an ARP packet through python on windows without needing winpcap?

Is there any way to send ARP packet on Windows without the use of another library such as winpcap?

I have heard that Windows XP SP2 blocks raw ethernet sockets, but I have also heard that raw sockets are only blocked for administrators. Any clarification here?


Source: (StackOverflow)

Doing ARP and Inverse ARP on Linux 2.6.21 (glibc 2.3.5)

I need to store persistent reference to third party device on an arbitrary IP network where the IP address of the devices may be static or randomly assigned by DHCP. I don't control the devices on the network and I can't rely on DNS and other ad-hoc networking protocols existing or working with the devices.

So I have been instructed to investigate using hardware addresses and ARP. This will work but I don't want to duplicate code. The kernel must manage an ARP table. On Windows you can access it using GetIpNetTable etc.

I am hoping there is an API to answer these two questions:

  • How do I translate from IP to MAC address? (ARP)
  • How do I translate from MAC to IP address? (InARP)

If not then I may have to do it more manually:

  • How do I read the kernel's ARP table?
  • How do I add an entry if I have the determined a mapping myself?

Source: (StackOverflow)

Adding arp bindings into ARP table Linux

Im trying to add an ARP binding into ARP table in linux, my arp table looks like this:

IP address       HW type     Flags       HW address            Mask     Device
192.168.3.12     0x1         0x6         00:0c:29:89:c5:cc     *        eth1
192.168.3.100    0x1         0x6         00:0c:29:89:c5:c8     *        eth1
192.168.43.2     0x1         0x2         00:50:56:e1:65:76     *        eth0
192.168.3.111    0x1         0x6         00:11:22:33:44:55     *        eth1
192.168.43.139   0x1         0x6         00:0c:29:89:c5:cc     *        eth0

this is what im trying to do, but i get the following error:

arp -s 192.168.43.138 00:00:22:33:33:33
SIOCSARP: Invalid argument

Any other IP addresses are working fine, just this one is resulting in an error Any ideas what is wrong here? (it is not a problem of mac address probably, ive tried many other addresses)


Source: (StackOverflow)

Get IP from MAC address. arp -a not showing device

I'm trying to write a batch file that's supposed to find the dynamically assigned IP of my Android phone when it's connected to the network (Tenda WiFi router).

So I'm trying arp -a and searching for my phone's MAC address so I can get its IP from the table.

C:\Users\Leeroy>arp -a

Interface: 192.168.0.100 --- 0xb
  Internet Address      Physical Address      Type
  192.168.0.1           c8-3a-35-35-f6-68     dynamic
  192.168.0.255         ff-ff-ff-ff-ff-ff     static
  224.0.0.22            01-00-5e-00-00-16     static
  224.0.0.251           01-00-5e-00-00-fb     static
  224.0.0.252           01-00-5e-00-00-fc     static
  239.255.255.250       01-00-5e-7f-ff-fa     static
  255.255.255.255       ff-ff-ff-ff-ff-ff     static

The problem is it doesn't show up in the table! I tried ping 192.168.0.255 but it still doesn't show up. I tried requesting 192.168.0.100 (IP of my desktop PC) from the phone's browser, and that sure enough puts the phone on the radar. But I don't have the option to manually do that everytime I want it to appear in the arp table.

How do I get the Android phone to appear in the arp table (without doing anything from it besides connecting to WiFi)?

SOLVED: Solved with ping. It takes no more than a second or two. EDIT 2: Updated some more. Here is the final batch file:

@echo off
:top
:: Loop through arp table entries and look for my Android device's MAC address
for /f "tokens=1-5 skip=3" %%f  in ('arp -a') do (if "%%g"=="xx-xx-xx-xx-xx-xx" set ip=%%f)

if "%ip%"=="" (
    echo Discovering network...
    :: Ping all IPs from 192.168.0.1 to 254
    for /L %%N in (1,1,254) do start /b ping -n 1 -w 200 192.168.0.%%N >nul
    timeout 1 >nul
    goto :top
) else (
    echo Mapping network location to drive K
    net use k: http://%ip%:8080 /user:francis underwood /persistent:no 
    if exist k: explorer k:
    :: Using FTP (please configure user and pass)
    :: explorer ftp://user:pass@%%f:6262 
    )
)

Source: (StackOverflow)