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Monitoring UDP data on wireshark shows ARP packet

asked 2017-11-27 16:25:43 +0000

updated 2017-11-27 16:41:59 +0000

grahamb gravatar image

Hello Everyone ,

I am trying to send UDP packet to my server 192.168.1.5 with port number 50001. I have implemented UDP client on PC and when i send data using sendto API , at the same time i monitor data on wireshark wireshark shows it as an ARP packet.

18967   5440.858646 PcsCompu_ef:b4:89   Broadcast   ARP 42  Who has 192.168.1.5? Tell 192.168.1.70

192.168.1.70 is my machine ip where UDP client is running.

I am not sure how UDP packet is getting converted into ARP packet ?

Any inputs are highly appreciated. Thanks in advance.

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answered 2017-11-27 16:41:41 +0000

grahamb gravatar image

To send a unicast (non-broadcast) packet over an Ethernet network requires the host to know the MAC address of the next hop and this is achieved with an ARP request.

If there is a host at the target address it will respond, providing its MAC address for the sending host to use.

If there is no host at the target address, there will not be an ARP response and the UDP packet will not be sent.

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Thanks for your response.

Yes, That´s correct.

In my case MAC of Target is already known , How can i provide this MAC so it directly starts UDP communicaton.

Target is camera device which will not be responding for such ARP request. So is there any way i directly provide MAC for target in my UDP client application ?

I appreciate your help.

Kapil Mehta gravatar imageKapil Mehta ( 2017-11-27 18:08:35 +0000 )edit

Most UN*X systems, and Windows, have an arp command, which you might be able to use to add the MAC address for the camera device to the local ARP table.

However, if the camera device doesn't respond to an ARP request, and it supports IPv4, it should probably be fixed to respond to an ARP request, so that it can be used from other machines whose users don't know about the arp command or don't know the MAC address of the camera.

Guy Harris gravatar imageGuy Harris ( 2017-11-28 00:49:55 +0000 )edit

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Asked: 2017-11-27 16:25:43 +0000

Seen: 56 times

Last updated: Nov 27