Local Network Problem

Nils Kassube kassube at gmx.net
Wed Aug 29 07:15:00 UTC 2007

Don Henson wrote:
> Eberhard Roloff wrote:
> > Don Henson wrote:
> >> To make a long background story short...
> >>
> >> In restoring from a major system crash, I ended up with a
> >> server/workstation, a workstation, and a laptop (wifi) that should
> >> be talking to each other over Ethernet. The laptop will not respond
> >> to a ping from anybody and the other two will respond to each
> >> other's pings if I use the domain address. They will not respond if
> >> I ping the corresponding IP address. This seems backwards to me but
> >> that's the way it is. At one point, I had all three machines talking
> >> but after rebooting all three, the problem returned. I've been
> >> working on this for a couple of days and now I find myself
> >> thoroughly confused. I have no idea which files and logs might be
> >> useful. If you are interested in helping, let me know what data you
> >> need and I'll post it forthwith. I'd really appreciate a little help
> >> on this one.
> >>
> >> Don Henson
> >
> > on each one:
> >
> > ifconfig eth0
> > cat /etc/hosts
> >
> > then: Do you use a dhcp server for your machines? (For example, your
> > router could be acting as such a server)
> >
> > do you use a firewall on all your machines or on specific machines?
> >
> > What does a packet sniffer, ex. ethereal show on your laptop, when
> > you try to ping it from another machine.
> >
> > If you are working with fixed ip addresses, what happes if you
> > connect only two machines via a crossover cable , i.e. leave out your
> > swith and anthing else in between.
> >
> > kind regards
> > Eberhard
> Per your request...
> For Earth-svr
> dhenson at Earth-svr:~$ ifconfig
> eth0      Link encap:Ethernet  HWaddr 00:07:E9:9C:26:0B
>           inet addr:  Bcast: 
> dhenson at Earth-svr:~$ cat /etc/hosts
> #     localhost

Please uncomment this entry, although it seems to be unrelated to your 

>    Earth-svr.site  Earth-svr       localhost

Localhost should be not the address of an external interface. It 
may work, but I think it is quite unusual.

>    Venus-ws.site   Venus-ws
>    Mars-laptop.site        Mars-laptop
> For Venus-ws
> jhenson at Venus-desktop:~$ ifconfig
> eth0      Link encap:Ethernet  HWaddr 00:15:F2:5B:9B:10
>           inet addr:  Bcast: 
> jhenson at Venus-desktop:~$ cat /etc/hosts
>       localhost
>    Earth-svr.site          Earth-svr
>    Venus-ws.site           Venus-ws
>    Mars-laptop.site        Mars-laptop
> For Mars-laptop
> dhenson at Mars-laptop:~$ ifconfig
> eth0      Link encap:Ethernet  HWaddr 00:19:B9:76:09:3C
>           inet addr:  Bcast: 
> wlan0     Link encap:Ethernet  HWaddr 00:19:7E:62:59:16
>           inet addr:  Bcast: 

Don't use two interfaces with the same IP address. That can't work. Please 
note: An IP address defines an interface, not a machine. Probably this is 
the reason why your laptop can't talk to anybody.

> dhenson at Mars-laptop:~$ cat /etc/hosts
> localhost
> Earth-svr.site Earth-svr
> Venus-ws.site Venus-ws
> Mars-laptop.site Mars-laptop.site
> The original install used DHCP but I am tryng to switch to static.
> My Linksys router/switch has a firewall. I use that and my machines
> have their firewalls turned off.

I don't see an entry for your router in any of your /etc/hosts files. You 
should add a line router.site router

to each of the files (I assume it has the address Otherwise 
you can't talk to the internet.

What is the output of the route command on your machines? It should look 
like this:

Kernel IP routing table
Destination  Gateway     Genmask         Flags Metric Ref    Use Iface  *    U     0      0        0 eth0
default      router.site         UG    0      0        0 eth0

The first line defines the local network, so you can talk to the other 
local machines. These machines can be reached directly without a gateway. 
The second line defines the rest of the world. To reach any non-local 
machine the data should be sent to the gateway router.site.

BTW: Why don't you want to use DHCP? It can make life so much easier. If 
you just don't want to use the built-in DHCP server of the router you 
could install a DHCP server e.g. on your Earth-svr machine.


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