Question

DISABLE LOOPBACK ON LINUX PC

Asked by: Newbie0000

Can anybody tell me how to disable the loopback on the fibre card in a Linux PC? The network has become inaccessible and we think that is the problem as it showing enabled now?

Thanks in advance for the help.

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Asked On
2009-09-01 at 09:17:42ID24698497
Topics

Linux Network Security

,

Linux

,

Linux Networking

Participating Experts
4
Points
500
Comments
8

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Answers

 

by: MiLLeNNiuMPosted on 2009-09-01 at 09:34:17ID: 25233292

To display the interfaces:
ifconfig -a

To disable it:
ifconfig INTERFACE down

 

by: Newbie0000Posted on 2009-09-01 at 09:59:13ID: 25233558

The NIC shows loopback enabled and he no longer has access to the network, is it because the loopback is enabled?

 

by: sanjoozPosted on 2009-09-01 at 10:14:55ID: 25233692

loopback being enabled has nothing to do with network being inaccessible. What exactly do you mean by network is inaccessible?

 

by: MiLLeNNiuMPosted on 2009-09-01 at 10:22:00ID: 25233766

It's quite confusing, could you paste the output for the following commands:

"ifconfig -a"
"route -n"

And also let us know what kind of access are you trying to do.

 

by: v_shalchianPosted on 2009-09-02 at 04:26:46ID: 25239779

To permanently disable loopback :
Go to /etc/sysconfig/network-scripts and edit ifcfg-lo
and change ONBOOT=yes to ONBOOT=no

 

by: Newbie0000Posted on 2009-09-02 at 09:48:37ID: 25242922

route -n
Kernal IP routing table
Destination   Gateway    Genmask   Flags Metric REf   Use Iface


ifconfig -a
eth0   link encap:ethernet  hwaddr 00:15:77:83:70:6c
      broadcast multicast  mtu:1500 metric:1
      rx packets:0 errors:0 dropped:0 overruns:0 frame:0
      tx packets:4 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000
      rx bytes: 0 (0.0b)   tx bytes:1368 (1.3kib)
      interrupt:22 base address:0xb000

lo Link ecncap:Local loopback
      inet addr:127.0.0.1 mask:255.0.0.0
      up loopback running  mtu:16436 metric:1
      rx packets:6 errors:0 dropped:0 overruns:0 frame:0
      tx packets: 6 error:0 dropped:0 overruns:0 carrier: 0
      collision:0 txqueulen:0
      rx bytes 300   tx bytes 300

 

by: sanjoozPosted on 2009-09-02 at 10:09:19ID: 25243134

So your network is inaccessible because you do not have an IP on your eth0. Are you using DHCP in your network? If your router is doubling as DHCP server, see if it is seup as a DHCP server.

Try also

ifconfig eth0 down
and
ifconfig eth0 up

 

by: it4sohoPosted on 2009-09-03 at 10:53:16ID: 25253098

In answer to an above question (though not THE question)... you need not even attempt to remove (or down) the lo (or on some systems lo0) interface. The so called "loopback" interface is present (and necessary) for linux network services to "talk" to one another (for example, the web server wanting to lookup an IP address using bind).

The lo interface will not affect any other interface, and has no hardware associated with it. To my knowledge, you CANNOT (and I should think that you SHOULD not) remove the network interface. The "hardware" for this interface is actually within the Kernel... so, again, you can dismiss it as being a source of your problem.

If you removed the hardware for your fibre card, then the output of your ifconfig shows that Linux is not attempting to use it. It also appears from your ifconfig output that your ethernet card is not properly configured (not sure how you got 1.3Kb of data to transmit while it has virtually no configuration)... but at a minimum, sanjooz is correct above -- you have no IP address in it, so it will NOT speak TCP/IP to anything else on the network (save for broadcasts).

I hope this helps shed SOME light

Dan
IT4SOHO

20120131-EE-VQP-002

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