# Disabling ARP Responses from Loopback Interface

## pato

I'm trying to set up a gentoo linux virtual server to load balance between a gentoo linux web server and a solaris web server. The LVS documentation says to disable ARP responses on the linux virtual loopback interface like so:

```

# echo "1" > /proc/sys/net/ipv4/conf/all/hidden

# echo "1" > proc/sys/net/ipv4/conf/lo/hidden

```

However, on my gentoo servers the 'hidden' file doesn't exist. On the solaris server, I was able to specify the -arp flag with ifconfig to disable ARP responses. I saw a similar flag described in the ifconfig manpage. However, even though I added it to my interface configuration, the loopback address is still replying to ARP requests. 

Does anyone know how to disable the loopback interface from responding to ARP requests?

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## pato

I think I've figured it out. I had created a virtual loopback interface:

```

# ifconfig lo:50 192.168.1.50 broadcast 192.168.1.255 netmask 255.255.255.255 -arp up

```

However, I noticed that the output of ifconfig -a looked odd:

```

lo        Link encap:Local Loopback

          inet addr:127.0.0.1  Mask:255.0.0.0

          UP LOOPBACK RUNNING  MTU:16436  Metric:1

          RX packets:0 errors:0 dropped:0 overruns:0 frame:0

          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

lo:50     Link encap:Local Loopback

          inet addr:192.168.1.50  Mask:255.255.255.255

          UP LOOPBACK RUNNING  MTU:16436  Metric:1

```

The NOARP flag doesn't show up.

So, I tried adding -arp to the non-virtual lo interface:

```

# ifconfig lo -arp

```

and saw satisfying results:

```

lo        Link encap:Local Loopback

          inet addr:127.0.0.1  Mask:255.0.0.0

          UP LOOPBACK RUNNING NOARP MTU:16436  Metric:1

          RX packets:0 errors:0 dropped:0 overruns:0 frame:0

          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

lo:50     Link encap:Local Loopback

          inet addr:192.168.1.50  Mask:255.255.255.255

          UP LOOPBACK RUNNING NOARP MTU:16436  Metric:1

```

Everything seems to working now (though I do get an annoying "Document Contains No Data" every once in a while). One problem down, yet another one to go.

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