[GRLUG] question about ping

[Michael Mol]

"Destination Host Unreachable" is an ICMP response for IP packets when
a router can't find a way to get the packet nearer to its destination.

These response packets may be filtered out by some network's
firewalls, in which case you might not hear anything back. If the
packet is passed on to the next router, and the next router never sees
it (or glitches in some other way), you may not hear anything back. If
the packet reaches the target host, but the target host is configured
to not send ICMP ECHO replies, you won't hear anything back.

I've also dealt with at least one system where the firewall was
configured to send an ICMP destination host unreachable response in
the case of a filtered port, rather than sending RST or silently
dropping the packet. _That_ one was puzzling.

On Thu, Mar 3, 2011 at 2:29 PM, Bill Littlejohn <billl at mtd-inc.com> wrote:
> When I ping some non-existent IP addresses I get Destination Host
> Unreachable, and some others return nothing.
> What's actually the difference?
>
> billl at MTD-IT-ADM2:~$ ping 192.168.1.113
> PING 192.168.1.113 (192.168.1.113) 56(84) bytes of data.
> From 192.168.1.210 icmp_seq=2 Destination Host Unreachable
> From 192.168.1.210 icmp_seq=3 Destination Host Unreachable
> From 192.168.1.210 icmp_seq=4 Destination Host Unreachable
> From 192.168.1.210 icmp_seq=5 Destination Host Unreachable
> From 192.168.1.210 icmp_seq=6 Destination Host Unreachable
> From 192.168.1.210 icmp_seq=7 Destination Host Unreachable
> ^C
> --- 192.168.1.113 ping statistics ---
> 8 packets transmitted, 0 received, +6 errors, 100% packet loss, time 7017ms
> , pipe 3
> billl at MTD-IT-ADM2:~$ ping 192.168.1.7
> PING 192.168.1.7 (192.168.1.7) 56(84) bytes of data.
> ^C
> --- 192.168.1.7 ping statistics ---
> 17 packets transmitted, 0 received, 100% packet loss, time 15999ms
>
>
>
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