[CentOS] Re: alias ip-addresses at loopback

Robert kerplop at sbcglobal.net
Mon Sep 15 16:44:10 UTC 2008



Robert Nichols wrote:
> Dmitry Cherkasov wrote:
>> Hello everybody!
>>
>> Could anybody advice on the following problem.
>> I need to assign several ip-addresses to 'lo' interface (beside
>> 127.0.0.1). It is convenient to me to implement NAT with such
>> addresses.
>
> The "lo" interface already accepts packets with any 127.x.y.z
> address.  Do you really need more addresses than the 127.0.0.0/8
> block?
>
>     $ ping -c1 127.111.222.123
>     PING 127.111.222.123 (127.111.222.123) 56(84) bytes of data.
>     64 bytes from 127.111.222.123: icmp_seq=1 ttl=64 time=0.104 ms
>
> I did absolutely nothing special to set that up.  I also routinely
> have an stunnel process listening on 127.0.0.25:465, and again, I
> did nothing special with the interface configuration or routing
> tables to allow that to work.
Any doubter can demonstrate that easily:
-----------

#!/bin/bash
#
z=1;y=0;x=0
while [ $x -le 255 ] ; do
y=0
while [ $y -le 255 ] ; do
z=1
while [ $z -le 255 ] ; do
  ping -c1 127.$x.$y.$z
(( z +=1 ))
done
(( y +=1 ))
done
(( x +=1 ))
done
---------------------
<snip>
PING 127.5.139.115 (127.5.139.115) 56(84) bytes of data.
64 bytes from 127.5.139.115: icmp_seq=1 ttl=64 time=0.051 ms

--- 127.5.139.115 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.051/0.051/0.051/0.000 ms
PING 127.5.139.116 (127.5.139.116) 56(84) bytes of data.
64 bytes from 127.5.139.116: icmp_seq=1 ttl=64 time=0.052 ms

--- 127.5.139.116 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.052/0.052/0.052/0.000 ms
PING 127.5.139.117 (127.5.139.117) 56(84) bytes of data.
64 bytes from 127.5.139.117: icmp_seq=1 ttl=64 time=0.051 ms

--- 127.5.139.117 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.051/0.051/0.051/0.000 ms
PING 127.5.139.118 (127.5.139.118) 56(84) bytes of data.
64 bytes from 127.5.139.118: icmp_seq=1 ttl=64 time=0.051 ms

--- 127.5.139.118 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.051/0.051/0.051/0.000 ms


...etc.


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