Who is ping talking to?

stf92 · 02-16-2013, 09:28 PM

Hi:

I have a LAN consisting of two hosts. Lets call one the server (or remote host) and the other the local host. Both are connected to internet through a router and modem. Running ifconfig in the server I get:

Code:

root@SERVER_HOST:~# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.101  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 fe80::922b:34ff:feb8:78cf  prefixlen 64  scopeid 0x20<link>
        ether 90:2b:34:b8:78:cf  txqueuelen 1000  (Ethernet)
        RX packets 114069  bytes 66498298 (63.4 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 245027  bytes 40631115 (38.7 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 42  base 0x4000  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 16436
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 740  bytes 43884 (42.8 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 740  bytes 43884 (42.8 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

If, in the local host I do 'ping 192.168.0.101', I get:

Code:

................................................
64 bytes from 192.168.0.101: icmp_seq=1 ttl=64 time=1.77 ms
.................................................

That is, the local host is talking to someone. The question is: whom is it talking?

wildwizard · 02-16-2013, 10:25 PM

Itself

stf92 · 02-16-2013, 10:27 PM

Why's that?

wildwizard · 02-16-2013, 10:28 PM

Because you told it to.

Do you think this is some sort of error?

stf92 · 02-16-2013, 10:34 PM

In the first code block, you see it says: 'inet 192.168.0.101'. And as I ran ifconfig in the server, it is some IP associated with the server, not with the local host. So when I do ping 192.168.0.101 from the local host, how can I be talking to the the local host? No, I do not say it's an error. I want to know what is 192.168.0.101.

wildwizard · 02-16-2013, 10:43 PM

Now I'm getting confused.

Try "arp -n" to see what IP addresses are local to a machine, anything that is routed via a router will not appear in this list.

stf92 · 02-16-2013, 10:47 PM

I get

Code:

root@SERVER_HOST:~# arp -n
Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.0.105                    (incomplete)                              eth0
192.168.0.1              ether   a0:f3:c1:59:06:2a   C                     eth0
root@SERVER_HOST:~#

e5150 · 02-16-2013, 10:48 PM

You ran `ifconfig` on the "server", and it says that the server is 192.168.0.101.
Then you ran `ping 192.168.0.101` from the "local host".
So given that both "server" and "local host" are on the same network (192.168.0.0/24), ping is talking to "server", who is 192.168.0.101.

stf92 · 02-16-2013, 10:54 PM

But in /etc/hosts (in the server) I have:

Code:

# For loopbacking.
127.0.0.1		localhost
127.0.0.1		SERVER_HOST.DN1 SERVER_HOST

# End of hosts.

And I do not see 192.168.0.101 in it. Besides, I, the server, am SERVER_HOST.DN1. So why is it not associated to 192.168.0.101 in /etc/hosts?

wildwizard · 02-16-2013, 11:04 PM

Well your hosts file is broken as it should have the real IP not the loopback one.

Also I smell a VPN here, am I right on that?

e5150 · 02-16-2013, 11:05 PM

/etc/hosts contains whatever you put in it (the defaults that comes with the etc-package only lists 127.0.0.1). Just about all computers see themselves as 127.0.0.1, it's the loopback interface (as you can see in the lo: section of the ifconfig output: "inet 127.0.0.1 netmask 255.0.0.0").
SERVER_HOST sees itself as 127.0.0.1, as does your other computer. It's eth0 with ip 192.168.0.101 on SERVER_HOST that your other computer can connect to SERVER_HOST through.

stf92 · 02-16-2013, 11:08 PM

I wanted to set the hostname and the domainname and could not do it. So I used netconfig and gave it those names. What it did I do not know, but after I ran it, /etc/hosts was as you see it. About VPN, honestly I don't know what it is.

e5150 · 02-16-2013, 11:20 PM

If you used netconfig to configure for the static ip 192.168.0.101 then /etc/hosts should contain a corresponding line. The setting you have seems to be what you get when setting up the network for dhcp with netconfig.

stf92 · 02-16-2013, 11:22 PM

Quote:

Originally Posted by e5150

/etc/hosts contains whatever you put in it (the defaults that comes with the etc-package only lists 127.0.0.1). Just about all computers see themselves as 127.0.0.1, it's the loopback interface (as you can see in the lo: section of the ifconfig output: "inet 127.0.0.1 netmask 255.0.0.0").
SERVER_HOST sees itself as 127.0.0.1, as does your other computer. It's eth0 with ip 192.168.0.101 on SERVER_HOST that your other computer can connect to SERVER_HOST through.

But who should SERVER_HOST.DN1 be for the local host. If I do rcp SERVER_HOST.DN1:some_file some_directory, on the local host (LOCAL_HOST.DN2), rcp must address some IP. What IP is that?

e5150 · 02-16-2013, 11:29 PM

Quote:

Originally Posted by stf92

but who should server_host.dn1 be for the local host. If i do rcp server_host.dn1:some_file some_directory, on the local host (local_host.dn2), rcp must address some ip. What ip is that?

192.168.0.101