[CentOS] testing a udp socket with netcat

Arif Hossain freefall1986 at gmail.com
Wed Mar 14 10:56:17 EDT 2012


On Wed, 2012-03-14 at 14:11 +0000, Giles Coochey wrote:
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> On 14/03/2012 13:59, Arif Hossain wrote:
> > On Wed, 2012-03-14 at 08:37 -0500, Les Mikesell wrote:
> >> On Wed, Mar 14, 2012 at 8:25 AM, Arif Hossain<freefall1986 at gmail.com> =
>  wrote:
> >>> i've this udp daemon which is waiting for an incoming udp datagram. n=
> ow
> >>> i want test this daemon for random garbage to test how it behaves. My=
> 
> >>> udp daemon is running because its shows on netstat. problem is if i
> >>> issue following command for putting udp datagram :
> >>> $nc -uvvz<host>  <port>
> >>>
> >>> it does not output any thing. i have straced the udp daemon. which do=
> es
> >>> not returns from recv() call.
> >>>
> >>> my goal is to ppience regarding netcat so i'm asking if anyone can he=
> lp me
> >>> out with this.
> >> Do you have iptables running?   The default config would probably
> >> block your udp traffic.
> >>
> > here is my iptable-rules
> >
> > # Generated by iptables-save v1.4.7 on Wed Mar 14 19:58:13 2012
> > *mangle
> > :PREROUTING ACCEPT [329554:95268521]
> > :INPUT ACCEPT [88918:46924677]
> > :FORWARD ACCEPT [0:0]
> > :OUTPUT ACCEPT [7296:1924138]
> > :POSTROUTING ACCEPT [7296:1924138]
> > COMMIT
> > # Completed on Wed Mar 14 19:58:13 2012
> > # Generated by iptables-save v1.4.7 on Wed Mar 14 19:58:13 2012
> > *filter
> > :INPUT ACCEPT [0:0]
> > :FORWARD ACCEPT [0:0]
> > :OUTPUT ACCEPT [206514:24743648]
> > -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
> > -A INPUT -p icmp -j ACCEPT
> > -A INPUT -i lo -j ACCEPT
> > -A INPUT -p tcp -m state --state NEW -m tcp --dport<port>  -j ACCEPT
> > -A INPUT -j REJECT --reject-with icmp-host-prohibited
> > -A FORWARD -j REJECT --reject-with icmp-host-prohibited
> > COMMIT
> > # Completed on Wed Mar 14 19:58:13 2012
> >
> And your INPUT chain rejects everything that is not matched by those=20
> lines above it.
> 
> You'll need a:
> 
> -A INPUT -p udp --dport <port> -j ACCEPT in there before you go to REJECT=
> =2E
> 
> --=20
> Best Regards,

for testing purpose i have flushed all rules in iptables -t filter

$iptables -t filter --flush

but still if try putting data by nc:

$nc -uvv localhost 7160

outputs :

write error: connection refused. 

> 

> Giles Coochey
> NetSecSpec Ltd
> UK Mobile: +44 7983 877 438
> Business Email: giles.coochey at netsecspec.co.uk
> Email/MSN/Live Messenger: giles at coochey.net
> Skype: gilescoochey
> 
> 
> 
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