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Old 07-30-2003, 03:06 AM   #1
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No Internet Connection From Private Network

greetings all! this is my first post, so here goes:

i am attempting to set-up a web server on a linux box running red hat 9.1. this machine is connected directly to the cable modem, and is the first machine hit as the internet connection comes into my network.

there are 2 nics in this machine - eth1 connects to the cable modem and is assigned an ip address dynamically by my isp; eth0 is connected by a crossover cable to the wan port on a linksys router (BEFSR41), which connects to 2 workstations (mac/2000win)

| ip provided by isp - eth1 |
| linux box
| - eth0 |
| - wan port |
| linksys router
| - lan ip |
| |
| |
----------------------- ----------------------
| -
| mac + win2000
---------------------- -----------------------

the issue is that i have no internet connection from the workstations. i do have an internet connection from the linux box.

from the linux box, i can ping

however, from a workstation, i can ping, but i can NOT ping

i have tried this after flushing all iptables chain policies so the system is completely open.

it seems the connection is broken from the router to the eth0 on the linux machine. any ideas? thanks in advance.
Old 07-30-2003, 06:42 AM   #2
Registered: Apr 2003
Location: Silicon Valley East, Northern Virginia
Distribution: FreeBSD,Debian, RH, ok well most of em...
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"however, from a workstation, i can ping, but i can NOT ping"

Can you ping from the linux box? And can you ping the outside world from the linux box?
Old 07-30-2003, 02:08 PM   #3
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from the linux box, i can ping

i also have an internet connection from the linux box, thus i can also ping the outside world.

i'm thinking it might be something to do with the firewall.

i tried flushing all the chains with:

iptables --policy INPUT ACCEPT
iptables --policy OUTPUT ACCEPT
iptables --policy FORWARD ACCEPT

iptables --flush
iptables --flush -t nat

however, with no chains established, do i need to still set a POSTROUTING rule?

can somebody tell me what's wrong with these commands:

modprobe iptables_nat
iptables -A POSTROUTING -t nat -o eth1 -j SNAT --to (ip adddress assigned by isp)

these commands are not working.

thanks for your reply
Old 07-31-2003, 08:19 PM   #4
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i guess it would help if i pointed out that the linux machine is also acting as a gateway/router (please excuse my newbiness for not pointing that out before.)

in addition, i performed tcpdump on both eth interfaces on the linux box:

eth0 receives packets when i ping or try to connect to the internet from the private network.

however, it appears that the ping is not replied to, and eth1 does not pass the packets to the default gateway.

can anybody point me in the right direction?

thanks again.


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