[CentOS] testing a udp socket with netcat

Cliff Pratt enkiduonthenet at gmail.com
Thu Mar 15 04:23:00 EDT 2012


On Thu, Mar 15, 2012 at 3:56 AM, Arif Hossain <freefall1986 at gmail.com> wrote:
> On Wed, 2012-03-14 at 14:11 +0000, Giles Coochey wrote:
>> --------------ms000000020507030501060609
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>> Content-Transfer-Encoding: quoted-printable
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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.
>
Is the UDP daemon listening on 127.0.0.1 (localhost)?

Cheers,

Cliff


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