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Old 11-23-2008, 10:31 AM   #1
Registered: Apr 2008
Posts: 114

Rep: Reputation: 15
ip_forward, routing

Hi, this is the scenario:

LAPTOP: eth0

PC has 2 interfaces: eth0 and eth1

Here the connections:

laptop(eth0) <--------> (eth0)PC(eth1)

PC has ip_forward = 0.

on "laptop" I type:

# route add -net eth0

Question is: why I'm able to ping if the ip_forwarding between the 2 interfaces is off?

Thank you.
Old 11-23-2008, 02:17 PM   #2
Registered: Dec 2004
Distribution: Slackware, Arch, FreeBSD
Posts: 202

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The PC is not forwarding packets if the packets are destined for the localhost, even if on a different interface.
Old 11-23-2008, 02:19 PM   #3
Registered: Feb 2008
Location: Texas
Distribution: Fedora, RHEL, CentOS
Posts: 488

Rep: Reputation: 78
because an IP really isnt "bound" to a specific interface. The kernel owns it and knows which interface to route the traffic.

Since the kernel "owns" both and it is able to properly respond on the 10. interface to your ping to since it does not require any forwarding to another network. It never leaves the PC system.
Old 11-24-2008, 07:10 AM   #4
Registered: Apr 2008
Posts: 114

Original Poster
Rep: Reputation: 15
Thank you!


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