Problem opening a listening port using netcat ( or other server )

Hi all,

My original problem was starting up a ruby on rails mongrel server but
I've tracked the problem back to the fact that I can't seem to set up
any process to listen on a port. I have tried netcat -l -p. But first
some details on me.

I have an Ubuntu Dapper laptop running NetworkManager to obtain a
wireless network connection to a WPA enabled router ( Netgear ). I am
perfectly able to make outgoing connections, ie surf the web, ssh to my
remote webserver account. No problems at all. Then I try to set up a
listening port on my local machine using netcat

netcat -l -p 1234

in another terminal I do

netcat 127.0.0.1 1234

and then type in the first terminal but nothing goes through. I have
also tried

netcat beermonster 1234
netcat 192.168.1.5 1234

but also no luck.

then I run netstat -al to find out what is up

tcp 0 0 *:1234 *:*
LISTEN
tcp 0 0 192.168.1.5:51730 72.14.217.99:www
ESTABLISHED
udp 0 0 *:bootpc *:*
raw 0 0 *:icmp *:*

netstat -r gives

Destination Gateway Genmask Flags MSS Window
irtt Iface
192.168.117.0 * 255.255.255.0 U 0 0
0 vmnet8
192.168.245.0 * 255.255.255.0 U 0 0
0 vmnet1
192.168.1.0 * 255.255.255.0 U 0 0
0 eth1
default 192.168.1.1 0.0.0.0 UG 0 0
0 eth1

netstat -i gives
Kernel Interface table
Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP
TX-OVR Flg
eth0 1500 0 0 0 0 0 0 0 0
0 BMU
eth1 1500 0 930 1 1 0 602 0 0
0 BMRU
vmnet 1500 0 0 0 0 0 6 0 0
0 BMRU
vmnet 1500 0 0 0 0 0 6 0 0
0 BMRU


Strangley too my machine does not respond to ping either.

ping 127.0.0.1
ping beermonster
ping 192.168.1.5

all do nothing.

It is like I have some magic firewall installed but I have never (
intentionally ) done such a thing. The only thing that I can think of
is that when vmware player installed it monkyed with my network
settings somewhere as it set up it's own virtual devices and thus broke
my machine but I am at a loss. Netcat says there is a port listening
but it doesn't seem to be doing anything?

Any help will be well regarded.

--
Brad Phelan
http://xtargets.com

2006-10-6, 11:51(-07), bradphelan:
[...]
> netcat -l -p 1234
>
> in another terminal I do
>
> netcat 127.0.0.1 1234
[...]
> netstat -i gives
> Kernel Interface table
> Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP
> TX-OVR Flg
> eth0 1500 0 0 0 0 0 0 0 0
> 0 BMU
> eth1 1500 0 930 1 1 0 602 0 0
> 0 BMRU
> vmnet 1500 0 0 0 0 0 6 0 0
> 0 BMRU
> vmnet 1500 0 0 0 0 0 6 0 0
> 0 BMRU
[...]

Your "lo" (loopback) interface doesn't seem to be configured

Try a:

ifup lo

or

ifconfig lo 127.1/8 up


--
Stéphane

Stephane CHAZELAS wrote:

> 2006-10-6, 11:51(-07), bradphelan:
> [...]
> > netcat -l -p 1234
> >
> > in another terminal I do
> >
> > netcat 127.0.0.1 1234
> [...]
> > netstat -i gives
> > Kernel Interface table
> > Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP
> > TX-OVR Flg
> > eth0 1500 0 0 0 0 0 0 0 0
> > 0 BMU
> > eth1 1500 0 930 1 1 0 602 0 0
> > 0 BMRU
> > vmnet 1500 0 0 0 0 0 6 0 0
> > 0 BMRU
> > vmnet 1500 0 0 0 0 0 6 0 0
> > 0 BMRU
> [...]
>
> Your "lo" (loopback) interface doesn't seem to be configured
>
> Try a:
>
> ifup lo
>
> or
>
> ifconfig lo 127.1/8 up
>
>
> --
> Stéphane

Thanks for the tip. I've added in the "lo" device

brad@beermonster:~$ netstat -i
Kernel Interface table
Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP
TX-OVR Flg
eth0 1500 0 0 0 0 0 0 0 0
0 BMU
eth1 1500 0 4331 1 1 0 3213 0 0
0 BMRU
lo 16436 0 0 0 0 0 0 0 0
0 LRU
vmnet 1500 0 0 0 0 0 6 0 0
0 BMRU
vmnet 1500 0 0 0 0 0 6 0 0
0 BMRU

but still netcat refuses to play ?

my /etc/network/interfaces files looks like

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

---

I can't think of any more information.

Brad

Stephane CHAZELAS wrote:

> 2006-10-6, 11:51(-07), bradphelan:
> [...]
> > netcat -l -p 1234
> >
> > in another terminal I do
> >
> > netcat 127.0.0.1 1234
> [...]
> > netstat -i gives
> > Kernel Interface table
> > Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP
> > TX-OVR Flg
> > eth0 1500 0 0 0 0 0 0 0 0
> > 0 BMU
> > eth1 1500 0 930 1 1 0 602 0 0
> > 0 BMRU
> > vmnet 1500 0 0 0 0 0 6 0 0
> > 0 BMRU
> > vmnet 1500 0 0 0 0 0 6 0 0
> > 0 BMRU
> [...]
>
> Your "lo" (loopback) interface doesn't seem to be configured
>
> Try a:
>
> ifup lo
>
> or
>
> ifconfig lo 127.1/8 up
>
>
> --
> Stéphane

You were right. It was the loopback device. Don't know why it didn't
work when I replied last time but I rebooted and it now seems up. The
strange thing is the problem is still there when I first foot the
machine. I have to

sudo ifdown lo
sudo ifup lo

before I can see the lo interface in with netstat -i. Just doing sudo
ifup lo gives me an error saying it is allready configured, probably
badly.

Thanks for the help.

Brad