# ARP behaviour at Gentoo

## Jenik

Hi,

I came across an interesting behaviour at Gentoo can someone explain me if I am wrong or if its standard behaviour?

If I dump ARP communication between FreeBSD and Gentoo, then FreeBSD send's ARP request(MAC1 and IP1 ???MAC2??? IP2) to datalink broadcast.Gentoo receives the request and replies but Gentoo sends ARP reguest for FreeBSD's IP afterwards which doesn't make sense cos Gentoo should already know the MAC of FreeBSD from the first FreeBSD's ARP request where the source MAC and IP (FreeBSD's MAC and IP) are included and should be saved into the ARP cache.

If the communication goes vice versa then FreeBSD handles request by ARP protocol.

What do you think about this behaviour ? Do I understand properly ? Isn't it a bad implementation of ARP ?   

Thank you

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## eccerr0r

I doubt this is a Gentoo issue, it's a Linux thing, and I think the Linux behavior is better.

It's only one ARP so I don't think it's that much of an overhead.  I think Linux does this to ensure that the first arp was not spoofed, if two machines respond with different macs for the same IP then something's wrong... Also someone couldn't maliciously fill the arp cache by dumping a zillion fake arp packets...

There may be an optimization but I think after the cache is populated it's not going to be that much overhead...

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