how to send gratuitous arp?

how to send gratuitous arp?

[Ian Zapczynski]

Hello all,

I have read often about how High Availability products will send a
gratuitous arp request across the network to update each system's arp
cache.  I understand the concept, but need to do this manually.  I don't
want a full HA product, but just to be able to update those on my
network quickly when I move an IP address from one machine to the other.

I am using Red Hat 7.2.  Is there a Linux command that can be used to
send a gratuitous arp request?  Can anyone shed light on how this is
done? 

Thanks much,

-Ian

Re: how to send gratuitous arp?

[Scott Taylor]

At 08:08 AM 26/08/2002, you wrote:
>Hello all,
>
>I have read often about how High Availability products will send a
>gratuitous arp request across the network to update each system's arp
>cache.  I understand the concept, but need to do this manually.  I don't
>want a full HA product, but just to be able to update those on my
>network quickly when I move an IP address from one machine to the other.
>
>I am using Red Hat 7.2.  Is there a Linux command that can be used to
>send a gratuitous arp request?  Can anyone shed light on how this is
>done?

Ethernet just does it for you.  There is no need to worry about arp.  You 
can test this yourself by running 'arp' on the Linux boxen while you change 
the IP on another machine.  Anytime you change a NIC or change an IP 
address on any machine running Ethernet, it's just sent automagically.  As 
long as your LAN runs properly, this shouldn't take more than a few 
nanoseconds to propagate.

Arpwatch will even send you an email when ever an IP address is changed on 
your LAN.