ubuntu as router, 2 nics, 2 lans, outside lan can not connect to inside lan

Question

How can I make LAN on 192.168.1.xxx (eth2) forward packets to other LAN (eth0) 10.42.0.19 (Win7 PC)?

Both the LANs are connected to Ubuntu PC. I can ping from PC connected to eth0 to PC connected to eth2. However, I can not ping from PC connected to eth2 to PC connected to eth0.

You can see tracert can complete on way but not other way. How to make that work?

This way from second Win7 works to first Win7:

C:\Users\scott>tracert 192.168.200.36

Tracing route to WIN7 [192.168.200.36]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  SCOTT-P5QC [10.42.0.1]
  2    <1 ms    <1 ms    <1 ms  wr850g.hr.cox.net [192.168.1.1]
  3    25 ms    24 ms    31 ms  WIN7 [192.168.1.100]
  4    18 ms    17 ms    40 ms  WIN7 [192.168.200.36]

Trace complete.

This way from first Win7 to second Win7 is broken:

C:\Users\scott>tracert 10.42.0.19

Tracing route to 10.42.0.19 over a maximum of 30 hops

  1    52 ms     1 ms     1 ms  hubrouter.westell.com [192.168.200.1]
  2    43 ms    98 ms    45 ms  192.168.1.1
  3    45 ms   105 ms    24 ms  SCOTT-PC [192.168.1.102]
  4  SCOTT-PC [192.168.1.102]  reports: Destination protocol unreachable.

Trace complete.

From first Win7 to Ubuntu router works:

C:\Users\scott>tracert 10.42.0.1

Tracing route to SCOTT-P5QC [10.42.0.1]
over a maximum of 30 hops:

  1   105 ms    <1 ms     4 ms  hubrouter.westell.com [192.168.200.1]
  2    19 ms    17 ms    33 ms  192.168.1.1
  3    35 ms    34 ms     5 ms  SCOTT-P5QC [10.42.0.1]

Trace complete.

netstat routes in Ubuntu router:

scott@scott-P5QC:~$ netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         wr850g.hr.cox.n 0.0.0.0         UG        0 0          0 eth2
10.42.0.0       *               255.255.255.0   U         0 0          0 eth0
link-local      *               255.255.0.0     U         0 0          0 eth0
192.168.1.0     *               255.255.255.0   U         0 0          0 eth2

Hand copy of LAN layout:

I have also posted this question at Ubuntu Forums

Answer 1

Solved by installing webmin. Then used it to reset iptables. Seriously, a great tool for administering the firewall.

webmin told me 2 rules were in the iptables which it could not understand, so I save iprules to a file, did a reset and all the 3 PCs can share files.

A defacto firewall is running all the time using iptables. So they must be modified.

scott@scott-P5QC:~$ sudo dpkg -i webmin_1.580_all.deb
Selecting previously unselected package webmin.
(Reading database ... 229686 files and directories currently installed.)
Unpacking webmin (from webmin_1.580_all.deb) ...
Setting up webmin (1.580) ...
Webmin install complete. You can now login to xxxxxxxxxxxxxxxxxxx
as root with your root password, or as any user who can use sudo
to run commands as root.
Processing triggers for ureadahead ...
ureadahead will be reprofiled on next reboot

To show what it looks like:

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Source - Ubuntu Geek