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Internet & Intranet (routing ?)

Posted on 2000-05-02
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Last Modified: 2008-03-10
Here's the situation (it's pretty common) :

We've got an intranet at home, and one PC which is running Linux (of course :-) and which has two network cards : one connected to a cable modem, one connected to the hub of our intranet. There is no problem with the connection to the internet, this all works fine, but I can't seem to ping to or from the PC with 2 cards to/from any other PC in the network.

The idea of course is to do IP masquerading, but that's not the question here. Question is : From my gateway PC, why can I ping to any Internet address, but not to any of the intranet computers ? Do I have to install a route daemon (if so, how ?) or is there another problem ?

The hardware all works fine, 'cause in Windows I can ping any address on the Internet as well as on the intranet.

FYI : When I ping, I get the message 'Destination host unreachable' and when I telnet from the gateway to another intranet-PC, it says 'No route to host'.

I hope someone can help me as it is pretty urgent.
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Question by:Jeeke
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Expert Comment

by:tibori
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The route daemon "routed" should already be loaded. What you should do is check your routing table using /sbin/route. You should have an entry in there that allows you to access your local intranet. If not you can add a route(as root) with the command:
/sbin/route add -net x.x.x.x netmask <yournetmask> -dev eth0(or eth1) whichever is the netcard linking you to your local net.
This command(depending on how you want to set it up)can give you access to your Windows PC or if you want to a whole subnet. Also make sure you're not IPMASQ-ing on your local net just to the outside. If you give more details,for example the result of /sbin/route I can tell you the exact command you need to use.
Good luck.
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Author Comment

by:Jeeke
Comment Utility
Here's the route output :

[root@homer /root]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.0.1        *               255.255.255.255 UH    0      0        0 eth1
195.162.213.0   *               255.255.255.0   U     0      0        0 eth0
10.0.0.0        *               255.0.0.0       U     0      0        0 eth1
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         gw-vlan-202.che 0.0.0.0         UG    0      0        0 eth0


I haven't made any changes to it, this is the routing table after I added both devices using linuxconf.
BTW, did I mention that I can't ping my gateway machine from any other PC's either ?

BTW2 : It is a clean Linux install.
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Author Comment

by:Jeeke
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After I run the routed, the route output is as follows :

[root@homer /root]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.0.1        *               255.255.255.255 UH    0      0        0 eth1
195.162.213.0   cable-195-162-2 255.255.255.0   UG    0      0        0 eth0
195.162.213.0   *               255.255.255.0   U     0      0        0 eth0
10.0.0.0        10.0.0.1        255.0.0.0       UG    0      0        0 eth1
10.0.0.0        *               255.0.0.0       U     0      0        0 eth1
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         gw-vlan-202.che 0.0.0.0         UG    0      0        0 eth0


Hope this helps too.
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Author Comment

by:Jeeke
Comment Utility
After I run the routed, the route output is as follows :

[root@homer /root]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.0.1        *               255.255.255.255 UH    0      0        0 eth1
195.162.213.0   cable-195-162-2 255.255.255.0   UG    0      0        0 eth0
195.162.213.0   *               255.255.255.0   U     0      0        0 eth0
10.0.0.0        10.0.0.1        255.0.0.0       UG    0      0        0 eth1
10.0.0.0        *               255.0.0.0       U     0      0        0 eth1
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         gw-vlan-202.che 0.0.0.0         UG    0      0        0 eth0


Hope this helps too.
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Expert Comment

by:unixway52
Comment Utility
What is the default gateway on the PC's on
the 10.0.0.0 network? They should be pointed at
10.0.0.1 if you're using the linux box as a
firewall/nat box.

The output from netstat -in would be useful as well.
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Accepted Solution

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jlevie earned 300 total points
Comment Utility
The output from "ifconfig -a" may well yield the answer. You might have a problem with your inside ethernet card. The routing tables are valid, and there is a route to the 10.0.0.0/8 network. So if you get "network unreachable" from within the gateway box, the most likely candidate becomes the NIC itself.
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Author Comment

by:Jeeke
Comment Utility
I'd like to thank you all for the help. Indeed, as jlevie said, I installed a different network card, and everything seems to work now. Apparently Linux has some problems with the ethernet card, as it worked in Windows without any problem. Anuway, the IP masquerading works as well, so everything is _finally_ working :-)

Thanks again
Jeeke
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