Sending ARP request to unicast MAC instead of broadcast MAC address?

James Hess mysidia at
Wed Jun 16 23:20:54 UTC 2010

On Wed, Jun 16, 2010 at 5:57 PM, Chris Woodfield <rekoil at> wrote:
> OK, this sounds Really Wacky (or, Really Hacky if you're into puns) but there's a reason for it, I swear...

> Will typical OSS UNIX kernels (Linux, BSD, MacOS X, etc) reply to a crafted ARP request that, instead of having FF:FF:FF:FF:FF:FF as its destination MAC address, is instead sent to the already-known unicast MAC address of the host?

In general, hosts respond to these in just the same way as they would
respond to a broadcast arp request.

> Next, what would be your utility of choice for crafting such a packet? Or is this something one would need to code up by hand in a lower-level language?

arping  from the iputils  package will switch to unicast requests
after the first unicast ARP response is received,  and send the rest
of the pings using unicast arp,  assuming you don't use the  -b


More information about the NANOG mailing list