Re: IP Takeover and ARP cache flush

[Vishwas Raman <vishwas@eternal-systems.com>]

Ravi Krishnamurthy wrote:
> --- Vishwas Raman <vishwas@eternal-systems.com> wrote:
> 
> 
>>After Machine 2 takes over Machine 2's IP,
>>all it needs to do is to send a ping to all the
>>clients of Machine 1, which is Machine 3 
>>in this case. According to the ARP RFC, Machine 3
>>at that point has to  flush its arp cache, and then 
>>register a new entry MIP1:MMAC2 in its arp 
>>cache. I even tested this by using the arp, ifconfig 
>>and ping commands and it works.
> 
> 
> If I understand it right, the ARP RFC does not
> say that an ICMP packet should be received for the
> ARP cache to be updated. Even if an ARP request is
> received, the ARP cache should be updated with the
> sender's address. And you could even send an ARP
> reply, without getting a request, to update other
> hosts' cache. This is called gratuitous ARP. I am not
> sure if Linux ARP implementation updates the cache
> when it receives gratuitous ARP packet.
> 
> -Ravi.
> 
> 

Are you suggesting that, all I need to do is send an ARP request to the 
other host for it to update its arp cache. Thanks for the input. I will 
look up the Linux ARP implementation, if I can get away with just 
sending a gratuitous ARP packet to the other host too.

-Vishwas.


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