New RedHat 5 installation at a university with Internet access via the
campus ethernet wiring. No firewall. RH5 box can SEE OUT to the Internet,
but nobody on the Internet can SEE IN to the RH5 box (ping, telnet).
The details:
RH5 Linux machine works fine, except that from outside of campus it cannot
be seen. Pinging it receives a timeout. Subnet mask is correct
(255.255.255.0). All other devices on the subnet are visible and
reachable, including a couple of Suns, SGI's, and Novell servers.
Restarted the Linux box several times.
(I've poured over all the unix docs I could find but haven't come across
anything that has helped identify or resolve the problem)
Running "ifconfig" provided a correct information for device "eth0" -- ip
address, bcast (138.23.43.255), and subnet mask (255.255.255.0). Compared
bcast & subnet mask with the Sun, which resides on the same subnet, and
they appear correct.
Output of the "ifconfig" command:
lo Link encap:Local Loopback
inet addr:127.0.0.1 Bcast:127.255.255.255 Mask:255.0.0.0
UP BROADCAST LOOPBACK RUNNING MTU:3584 Metric:1
RX packets:428 errors:0 dropped:0 overruns:0
TX packets:428 errors:0 dropped:0 overruns:0
eth0 Link encap:Ethernet HWaddr 00:60:08:66:9D:A2
inet addr:138.23.43.123 Bcast:138.23.43.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:26771 errors:0 dropped:0 overruns:0
TX packets:3589 errors:0 dropped:0 overruns:0
Interrupt:10 Base address:0x6500
I manually set the "mask" and "bcast" fields by modifying the
"/etc/sysconfig/network-scripts/ifcfg-eth0" file. Had to modify the file
because did not see any other way to set the "mask" and "bcast" fields.
(Is there another, better way of setting these fields?)
Mask and Bcast addresses are correct:
The netmask and broadcast address are correct for our network. To verify
that I performed an "ifconfig -a" on one of the Suns (running Solaris 2.5)
on the same subnet and verified it uses the same bcast & mask.
Default Gateway looks correct:
The X Window "Network Configurator" "Routing" option has the "default
gateway" listed as "138.23.43.1", which is the correct address of the
router on this particular subnet. "default gateway device" is "eth0".
It's not the ethernet wiring:
Tried a different ethernet jack with a different ethernet cable and
received the same results. Connected the Sun to the same ethernet
connection the Linux box uses (with the same ethernet cable) and it worked
just fine.
DNS servers are working:
Performing the "nslookup" command from the Linux box found the campus DNS
server correctly. (The DNS server is on a different subnet).
(1) Any idea why the machine cannot be seen outside of the local subnet?
Did I miss something during the configuration?
(2) The X Window "Network Configurator" utility's "Routing" option has a
selection titled "Network Packet Forwarding (IPv4)". What does that do?
Is it used only if the RH5 machine is used as a router? Or, could it be
the reason the machine cannot be seen from the Internet?
THANK YOU FOR YOUR ASSISTANCE!
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