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Old 07-30-2004, 07:18 AM   #1
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Registered: Jul 2004
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Can ping into box but not out of box

Red Hat Linux 9.0

I am connected to my ISP via a wireless radio. They have issued two public IP's. However, the IP address that I actually use on the two boxes I have connected to the internet are in the private range 172.16.46.XX.

The wireless modem is connected to a switch. The two boxes are connected to a switch. The gateway IP is, netmask is The first box (NT) works fine when I use either IP address the ISP told me to use ( which maps to and which maps to Neither works correctly when I use it on the Linux box.

On the linux box I have verified the interrupt on the card ( = 11 when it boots). In network config it is set to 11. HOWEVER IFCONFIG SHOWS INTERRUPT AS 22. I have tried deactivating and activating eth0 but the interrupt does not change as shown in ifconfig. I cannot set the interrupt to 22 in network config. Setting it to 11 or unknown does not change the symptoms. The card is a natsemi DP3815 (Netgear). Motherboard is ABIT 1S7-G with APIC version 1.4 enabled. The PCI bus also has an Adaptec 29160 on it, nothing else. When the system boots the interrupt shown associated with network card is 11. The boot information does not show that any other device uses that interrupt.

I have disabled the firewall. iptables -L -n shows no filters.

The symptoms are as follows:
I cannot ping the gateway IP (at least no response is received) from the linux box.

I cannot ping anything else either (other than IP of the linux box itself)

No other IP protocol works on the linux box.

I can ping and receive a response when I ping the IP (the
linux box) from IP (the NT box)

I can ping and receive a response when I ping the mapped IP (= of the linux box from the NT box.

I can even ssh into the linux box (using from any
NT box on my lan via the NT box gateway ( =

After I ping either the NT box or the gateway IP from the linux box,
arp -a -n on the linux box shows the correct mac address associated
with those IP's even though I receive no response.

When I ping the linux box from the NT box. The NT box receives replies,
but running tcpdump on the linux box at the same time shows NO echo
packets received or replied to. The same happens when I ssh into the
linux box (works, but tcpdump logs no packets)

I am mystified.
Old 07-30-2004, 07:32 AM   #2
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Registered: Jul 2004
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changing interrupt does not work

I manually set the interrupt of the PCI slot that has the net card to 9. Changed bios APIC version from 1.4 to 1.1. Changed network config to use interrupt 9. ifconfig now shows interrupt as 9. Same symptoms as above.
Old 07-30-2004, 07:39 AM   #3
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Registered: Jul 2004
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tcpdump does show echo request / reply

After changing the interrupt to 9 one symptom changed. When I ping the ip of the linux box, tcpdump shows the echo request and reply. I still cannot ping out (destination host unreachable) when I ping the gateway.

route --inet shows * U 0 0 0 etho * U 0 0 0 eth0 * U 0 0 0 lo
default UG 0 0 0 eth0


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