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Old 03-11-2013, 04:13 PM   #1
LQ Newbie
Registered: Jan 2011
Location: Austin, TX
Posts: 29

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Gateway computer configuration question

I have the following network configuration, with computer 1 connected to computer 2, which is connected to the Internet.

Computer 1
default gateway:

Computer 2
eth1: XXX.XXX.XXX.27
default gateway: XXX.XXX.XXX.254

Routing table on Computer 2:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface * U 0 0 0 eth3
XXX.XXX.XXX.0 * U 0 0 0 eth1 * U 0 0 0 eth2 * U 0 0 0 eth0
default XXX.XXX.XXX.254 UG 0 0 0 eth1

I have a firewall on Computer 2 that basically looks like this:

I want Computer 1 to be able to connect to the Internet through Computer 2. As a first step, I just want to be able to get a ping response from eth1 on Computer 2 from Computer 1. I can get a ping response from eth2, but not eth1. When I run tcpdump on Computer 2 I can see an ICMP request come in on eth0 and an ICMP reply come in on eth1, but I never see an ICMP reply go out on eth0.

Can anyone see what I need to add in order to be able to get a ping response from eth1 on Computer 1?

Old 03-11-2013, 09:38 PM   #2
Registered: May 2008
Location: Toronto
Distribution: Centos && Debian
Posts: 347

Rep: Reputation: 34
The firewall on that link has the rule
# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth1 -o eth1 -j REJECT
It seems this rule is causing the problem. Outside interface is eth0 but in this rule it is eth1, that does not seem correct. Can you try after replacing -i eth1 to -i eth0 in this rule?
Old 03-12-2013, 11:49 AM   #3
LQ Newbie
Registered: Jan 2011
Location: Austin, TX
Posts: 29

Original Poster
Rep: Reputation: 2
Thanks for your reply.

I ended up just giving up on getting a ping response from eth1, and just continuing on with my ultimate goal of getting from Computer 1 out to the Internet. For that purpose, everything works, so I'm not going to worry about it.



debian, firewall, gateway, routing

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