Hello,

I am a fairly new Lunux user.

I am trying to setup a test netork as follows:

172.16.4.0 ---> | eth0_inside (172.16.4.2)-- Redhat 9 Box -- eth1_toRouter (172.16.3.10)| ---> router (172.16.3.4)

eth0_inside IP is 172.16.4.2. The default gateway has the eth1_toRouter's IP 172.16.3.10.

eth1_toRouter IP is 172.16.3.10 and its default gateway is the
router's IP 172.16.3.4.

I edited the sysctl.conf file in /etc to put a value of '1' to
net.ipv4.ip_forward. I rebooted the machine.

Result:

I can ping both interfaces, the router, and the inside hosts
from the linux box.

The hosts can ping only up to eth1_toRouter (172.16.3.10). Not
beyond that.

Your help would be greatly appreciated.


Some output:

[root@localhost log]# cat /proc/sys/net/ipv4/ip_forward
1

[root@localhost log]# netstat -nr
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
172.16.4.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
172.16.3.0 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 eth1
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 172.16.3.4 0.0.0.0 UG 0 0 0 eth1

[root@localhost log]# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:60:97F:8A:82
inet addr:172.16.4.2 Bcast:172.16.4.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:246 errors:0 dropped:0 overruns:0 frame:0
TX packets:22 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:28775 (28.1 Kb) TX bytes:1488 (1.4 Kb)
Interrupt:11 Base address:0xdcc0

eth1 Link encap:Ethernet HWaddr 00:06:5B:B5:86:A9
inet addr:172.16.3.10 Bcast:172.16.3.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:505 errors:0 dropped:0 overruns:0 frame:0
TX packets:174 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:45158 (44.0 Kb) TX bytes:18754 (18.3 Kb)
Interrupt:11 Base address:0xdc00

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:15309 errors:0 dropped:0 overruns:0 frame:0
TX packets:15309 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1044830 (1020.3 Kb) TX bytes:1044830 (1020.3 Kb)

I can't tell from reading your post what the contents of
/etc/sysconfig/network are, on the RH9 box. The line which
starts GATEWAY= should have the address 172.16.3.4, the
address of your router (not the machine's eth1 number).

Result:

I can ping both interfaces, the router, and the inside hosts
from the linux box.

OK!

The hosts can ping only up to eth1_toRouter (172.16.3.10). Not
beyond that.

OK!

Your help would be greatly appreciated.

The routing tables from your linux box look correct based on your network description. But you have not shown the routing tables from the router at 172.16.3.4. Based on the above mentioned results, it sounds like the router at 172.16.3.4 does not know how to route packets (like ACKS) back to network 172.16.4.0/24. i.e. via 172.16.3.10