On 02/13/2013 10:43 PM, inode0 wrote:
On Wed, Feb 13, 2013 at 7:57 AM, Ed Greshko
> One thing of interest to note but which may not affect what the OP is doing....
> If the port being tested is listed as "filtered" by nmap
> [egreshko@meimei ~]$ nmap -Pn -p143 imap.gmail.com
> Starting Nmap 6.01 ( http://nmap.org
) at 2013-02-13 21:53 CST
> Nmap scan report for imap.gmail.com
> Host is up.
> Other addresses for imap.gmail.com
(not scanned): 18.104.22.168
> rDNS record for 22.214.171.124: oa-in-f108.1e100.net
> PORT STATE SERVICE
> 143/tcp filtered imap
> the command
> 2>/dev/null >/dev/tcp/imap.gmail.com/143 && echo "yes"
> will hang for quite some time....
I don't think this is related to the port being filtered as other
sites with filtered ports return quickly (same is true of down hosts).
Perhaps it is some other rude firewall behavior that causes the
Well, basically, what the command is doing is causing a SYN packet to be sent out. If the
host is down or the firewall doesn't send an RST,ACK it will "hang" until it
So, since the OP is using to test if a system is "alive" a "dead"
system will cause a substantial delay before timing out.
Don't be bullied by the judgmental grammar and spelling police.