Static Routing Problem

kewlemer · 07-02-2006, 03:36 PM

I am trying to have box A and box C communicate on a set up like this :-

Code:

------------------------------------------------------
[Box A] <==========> [Box B] <===========> [Box C]
------------------------------------------------------
192.168.1.103<---->192.168.1.101    
255.255.255.0      255.255.255.0
eth0               eth1
------------------------------------------------------
                   192.168.2.1<--------> 192.168.2.2
                   255.255.255.0         255.255.255.0
                   eth2                  eth0
------------------------------------------------------
                   192.168.1.100
                   255.255.255.0
                   eth0
                   [to Internet]
------------------------------------------------------

Here is the routing table on B :-

Code:

[root@localhost ~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.2.0     192.168.2.2     255.255.255.0   UG        0 0          0 eth2
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.1.0     192.168.1.103   255.255.255.0   UG        0 0          0 eth1
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth2
0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 eth0
[root@localhost ~]#

Here is the routing table on A :-

Code:

[root@localhost ~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
0.0.0.0         192.168.1.101   0.0.0.0         UG        0 0          0 eth0
[root@localhost ~]#

Here is the routing table on C:-

Code:

[root@postel ~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 eth0
[root@postel ~]#

Any anyone see something wrong here that is preventing A and C from communicating ?

Please note that A and B can communicate; so also B and C. But NOT A and C.

Thank you very much,
K

acid_kewpie · 07-02-2006, 04:41 PM

the first two bold routes on B don't make any sense. that machine is already on those networks yet you are somehow telling to route to the local network via another box??? the only route B needs is a default out to the net as everythign is locally attached an implicitly known to it. also i assume you have enabled ip forwarding?

fataldata · 07-02-2006, 04:58 PM

Acid_kewpie is right to ask whether ip forwarding is enabled first. If it is, well then I probably would not use the same networks for A and B as you are using for B and the internet.

When A tries to ping C with 192.168.2.2 the packet arrives at machine B where the route is directing packets for network 192.168.2.0/24 to 0.0.0.0 the default gateway which by the last line is Eth0 going to the internet.

Just my 2 cents.

kewlemer · 07-02-2006, 05:56 PM

Thanks a ton for the responses folks. You guys were right in asking me if I had IP forwarding enabled. I had'nt

. Used this thread to set it up :-

http://www.linuxforums.org/forum/red...orwarding.html
Actually I just put net.ipv4.ip_forward = 1 in /etc/sysctl.conf .

This is the routing table on B:-

Code:

[root@localhost ~]# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.3.0     0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth1
0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 eth0
[root@localhost ~]#

I moved A and eth1(on B) onto 192.168.3.*; C and eth2(on B) on 192.168.2.* bacause of the bold line entry which came up each time I configured the default route on eth0 (192.168.1.1).

The set-up works now.

Thanks again,
K