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anthillsocial

Member

Registered: 2013-02-18

Posts: 129

[SOLVED] Netcat fails to connect to port on localhost

I was just performing a quick socket test on a Raspberry Pi using netcat:

nc -l -p 2007

Yet when I try and connect to the socket with netcat I get the following output and netcat immediately closes.

$ nc localhost 2007
----------------------------
Notice: Real hostname for localhost [127.0.0.1] is localhost.localdomain
Notice: Real hostname for localhost [127.0.0.1] is localhost.localdomain
Total received bytes: 0
Total sent bytes: 0

Using netstat I can see the socket gets created

netstat -tulnap | grep 2007
--------------------------
tcp        0      0 0.0.0.0:2007            0.0.0.0:*               LISTEN      2369/nc  

And if I connect from a different machine on the same network it all works as expected:

$ nc 192.168.2.6 2008 -vv
Warning: Inverse name lookup failed for `192.168.2.6'
192.168.2.6 2008 (conf) open

What on earth could be happening? Is it something to do with the Inverse name lookup failure?

For reference here's the output of ifconfig:

eth0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether b8:27:eb:7e:39:0f  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 16436
        inet 127.0.0.1  netmask 255.0.0.0
        loop  txqueuelen 0  (Local Loopback)
        RX packets 18  bytes 1512 (1.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 18  bytes 1512 (1.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.2.6  netmask 255.255.255.0  broadcast 192.168.2.255
        ether e0:46:9a:2b:2c:ca  txqueuelen 1000  (Ethernet)
        RX packets 47753  bytes 12152129 (11.5 MiB)
        RX errors 0  dropped 48362  overruns 0  frame 0
        TX packets 37084  bytes 6283782 (5.9 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Last edited by anthillsocial (2013-10-18 22:22:12)

anthillsocial

Member

Registered: 2013-02-18

Posts: 129

Re: [SOLVED] Netcat fails to connect to port on localhost

I discovered that there's a bug with netcat on ARM architecture:
http://archlinuxarm.org/forum/viewtopic.php?f=9&t=1499

To solve the issue I swapped the gnu version of netcat with the openbsd version and it now works as expected:

sudo pacman -S openbsd-netcat

anthillsocial

Member

Registered: 2013-02-18

Posts: 129

Re: [SOLVED] Netcat fails to connect to port on localhost

Here's a link to the bug which was reported in 2005!
Though the suggested patch doesn't seem to have been incorporated:
http://sourceforge.net/p/netcat/bugs/23

What can be done to fix it?