What is chain Postrouting?
POSTROUTING chain – Alters packets after routing. i.e Packet translation happens when the packets are leaving the system. This helps to translate the source ip address of the packets to something that might match the routing on the desintation server. This is used for SNAT (source NAT).
What is a NAT chain?
The NAT table is vital to your internet connection. The network address translation (NAT) table is what allows devices on a private network to access a public network, such as the internet. There is often only one entry point between the public network and the private network, and that entry point is usually a router.
What is the difference between Prerouting and Postrouting?
PREROUTING: Immediately after being received by an interface. POSTROUTING: Right before leaving an interface. FORWARD: For any packets coming in one interface and leaving out another.
What is the role of the PREROUTING chain in Nat?
As the name implies, the PREROUTING chain is responsible for packets that just arrived at the network interface. So far no routing decision has taken place, therefore it is not yet known whether the packet would be interpreted locally or whether it would be forwarded to another machine located at another network interface.
What is the difference between Nat OUTPUT chain and iptables?
The green boxes are for iptables, the blue are for ebtables(ignore those). So you see that the OUTPUTchain is only traversed for packets produced by local applications, while the POSTROUTINGchain is traversed by all packets, including those routed from somewhere else.
What’s the difference between locally generated packets and PREROUTING chain?
For locally generated packets there is a small difference: Instead of passing through the PREROUTING chain it passes the OUTPUT chain and then moves on to the POSTROUTING chain. Before we start with our packet manipulations we have to enable the required features.
Can a NAT OUTPUT chain be used for DNAT?
That said, packets incoming from a network interface are apparently treated the same way as packets “incoming” from an application to the kernel through the OUTPUT chain, hence both can do DNAT.– dirktJun 28 ’19 at 5:57 Indeed, I can see herea brief mention that the OUTPUT chain can be used for DNAT.