Yeah, I tend to agree with you. In fact, for the most part, your are
indeed correct. But the rate can still be effected...
ping only does a lookup on the hostname in order to be able to send the
ping, at the start, when the command is invoked.
However, it does a lookup on every REPLY it receives. i.e. when it gets
the reply to a ping it has sent it, say it comes back from 126.96.36.199,
it does a lookup on that address before it displays it to you. This is why
you see hostname (ipaddress) in the output.
Its quite easy to demonstrate this. Below I start a ping to ns.iol.ie,
while the ping is still running, I block outbound requests on port 53
(i.e. stop it from doing DNS lookups). Watch what happens...
64 bytes from ns.iol.ie (188.8.131.52): icmp_seq=9 ttl=247 time=21.9 ms
64 bytes from ns.iol.ie (184.108.40.206): icmp_seq=10 ttl=247 time=20.8 ms
64 bytes from ns.iol.ie (220.127.116.11): icmp_seq=11 ttl=247 time=15.7 ms
64 bytes from 18.104.22.168: icmp_seq=12 ttl=247 time=27.2 ms
64 bytes from 22.214.171.124: icmp_seq=13 ttl=247 time=15.7 ms
64 bytes from 126.96.36.199: icmp_seq=14 ttl=247 time=15.4 ms
So as we can see, it does do DNS lookups in real time on the reply
address. But not, as you pointed out, on the destination host at each
 Keeping the auld iptables thing going, here is the rule I used...
# iptables -A OUTPUT -o eth0 -p udp -m udp --dport 53 -j DROP
On Wed, 22 Oct 2003, David Dorgan wrote:
>> This is a pretty strange situation, the rate should only
> effect it on startup, gethostbyname isn't called for
> every ping sent out.
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