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Groups > comp.os.linux.networking > #1560

Re: IP traffic between two NICs on same box

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Pascal Hambourg wrote:
 > Hello,
 >
 > Giro a écrit :
 >> >
 >> >  Is there any way to let two local network interfaces communicate with
 >> >  each other without using the loopback device?
 > Not easily.
 > First, the kernel forces packets with a local destination address
 > through the loopback interface. Second, the kernel discards packets
 > received on a non-loopback interface with a local source address.
 >
 >> >  On the same computer, I have interfaces eth1 (192.168.0.11) and eth2
 >> >  (192.168.0.12).  I want to
 >> >  ping from eth1 to eth2, and make the packet physically hit the wire,
 >> >  instead of going through the loopback device.
 > The above restrictions can be worked around with iptables NAT rules and
 > static ARP entries, tricking the kernel into believing that it is
 > communicating with a remote host. Sensitive people beware : what follows
 > is ugly.
 >
 > Say that "remote" eth1 will be seen as 192.168.0.21 and "remote" eth2 as
 > 192.168.0.22.
 >
 > # make sure packets to "remote" addresses are routed through the correct
 > # interface
 > ip route add 192.168.0.21 dev eth2
 > ip route add 192.168.0.22 dev eth1
 >
 > # create static ARP entries for the remote addresses
 > arp -s 192.168.0.21 $eth1_mac_address
 > arp -s 192.168.0.22 $eth2_mac_address
 >
 > # replace the source address of outgoing packets with the "remote"
 > # addresses
 > iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to 192.168.0.21
 > iptables -t nat -A POSTROUTING -o eth2 -j SNAT --to 192.168.0.22
 >
 > # replace the destination address of incoming packets with the real
 > # local addresses
 > iptables -t nat -A PREROUTING -i eth1 -j DNAT --to 192.168.0.11
 > iptables -t nat -A PREROUTING -i eth2 -j DNAT --to 192.168.0.12
 >
 > With this a packet sent to 192.168.0.21 or 192.168.0.22 and its reply
 > should go on the wire.


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IP traffic between two NICs on same box Harald Radke <looxrat@googlemail.com> - 2012-07-29 02:04 -0700
  Re: IP traffic between two NICs on same box Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2012-07-29 22:56 +0300
    Re: IP traffic between two NICs on same box looxrat@googlemail.com - 2012-07-29 13:32 -0700
      Re: IP traffic between two NICs on same box Moe Trin <ibuprofin@painkiller.example.tld.invalid> - 2012-07-29 20:43 -0500
        Re: IP traffic between two NICs on same box Robert Nichols <SEE_SIGNATURE@localhost.localdomain.invalid> - 2012-07-30 08:15 -0500
          Re: IP traffic between two NICs on same box Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2012-08-04 12:52 +0200
        Re: IP traffic between two NICs on same box Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2012-08-04 12:49 +0200
  Re: IP traffic between two NICs on same box Rick Jones <rick.jones2@hp.com> - 2012-07-30 17:46 +0000
  Re: IP traffic between two NICs on same box unruh <unruh@invalid.ca> - 2012-07-30 17:57 +0000
  Re: IP traffic between two NICs on same box ein <ein@no.spam> - 2012-08-05 14:26 +0200
    Re: IP traffic between two NICs on same box Pascal Hambourg <boite-a-spam@plouf.fr.eu.org> - 2012-08-05 14:59 +0200
      Re: IP traffic between two NICs on same box ein <ein@no.spam> - 2012-08-05 15:32 +0200
        Re: IP traffic between two NICs on same box ein <ein@no.spam> - 2012-08-05 15:34 +0200

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