Home / server / Questions / 204922
Accepted
kagali-san
Asked: 2010-11-23 14:36:58 +0800 CST

IPTables/Masquerade, making Linux kernel to see duplicate packets

  • 772

Will this rules make kernel to see the same packet at least twice?

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE                                                                   
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE

Found the stuff in a forgotten config file. A remark about option "-d 0/0" was also there, did this option makes sense when certain log targets are used in iptables - to avoid incorrect traffic calculation?

iptables

2 Answers

  1. Best Answer

    No, packets will not be seen twice. Only one of those two iptables rules will ever match a given packet, since a packet cannot exit the system by two different network interfaces at the same time. The routing algorithm always selects (at most) one output interface.

    • 0

  2. -o specifies that a particular packet is to be tested for its interface, it does not specify that a packet is to leave by that interface. (The latter would be routing and is controlled by ip route.)

    • -1