What is Linux kernel architecture?

The Linux kernel is one layer in the architecture of the entire Linux system. The kernel is conceptually composed of five major subsystems: the process scheduler, the memory manager, the virtual file system, the network interface, and the inter-process communication interface.

What are Netfilter hooks?

The Netfilter framework provides a series of “hooks” inside the Linux kernel network stack that are traversed by network packets (Figure 1). When a network packet is received on a network device, it first passes through the Prerouting hook. This is where the routing decision takes place.

What are the five netfilter hooks for ipv4?

The module can then tell netfilter to do one of five things:

NF_ACCEPT: continue traversal as normal.
NF_DROP: drop the packet; don’t continue traversal.
NF_STOLEN: I’ve taken over the packet; don’t continue traversal.
NF_QUEUE: queue the packet (usually for userspace handling).
NF_REPEAT: call this hook again.

Can netfilter be used to modify packets?

Once that Vagrant VM is setup, we can install a kernel module that uses Netfilter to modify packets on the fly.

What is Netfilter in Linux kernel?

Netfilter is the name of the kernel interface for capturing network packets for modifying/analyzing them (for filtering, NAT, etc.). The netfilter interface is used in user space by iptables. In the Linux kernel, packet capture using netfilter is done by attaching hooks.

What is the architecture of Netfilter?

Netfilter Architecture. Netfilter is merely a series of hooks in various points in a protocol stack (at this stage, IPv4, IPv6 and DECnet). The (idealized) IPv4 traversal diagram looks like the following: A Packet Traversing the Netfilter System: —>[1]—>[ROUTE]—>[3]—>[4]—> | ^ | | | [ROUTE] v | [2] [5] | ^ | | v |.

How many netfilter kernel hooks are there?

There are only five netfilter kernel hooks, so chains from multiple tables are registered at each of the hooks. For instance, three tables have PREROUTING chains. When these chains register at the associated NF_IP_PRE_ROUTING hook, they specify a priority that dictates what order each table’s PREROUTING chain is called.

What is the difference between iptables and Netfilter?

What Are IPTables and Netfilter? The basic firewall software most commonly used in Linux is called iptables. The iptables firewall works by interacting with the packet filtering hooks in the Linux kernel’s networking stack. These kernel hooks are known as the netfilter framework.