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Re: ping reply without OS (was: Re: Unidentified subject!)

Mario Olimpio de Menezes writes:
 > 	I experienced such situation when my nameserver was down for a
 > warm reboot, so that I couldn't telnet to it, but ping got response from
 > the machine during the reboot. I can't explain such situation, but it is
 > quite strange to me.

Nothing strange about it. There's a thing called Address Resolution Protocol
(arp), which maps IPs to MAC (network card) addresses. It makes TCP/IP work
over your ethernet. Try this:

# arp -a

You'll see that you have a table mapping local IPs to MACs (the ethernet
protocol doesn't understand IP addresses, only MAC ones). So, to send a
datagram to your name server, you need its MAC address, which already was in
your arp table.

Now, the OS wasn't fully operational, some services (inetd) weren't available
yet, but the kernel and the tcp layer were there, answering pings (which uses
the ICMP protocol).


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