Iptables

iptables

Tables

Main tables are Filter, NAT, Mangle

• Filter - default
• NAT
• Mangle - change IP Headers

Chains

Traversal Order: Pre --> Input --> Forward --> Output

• Prerouting - Incoming packet
• Input - Entering network stack
• Forward - Routed through system
• Output - Orginated on system and leaving system
• Post Routing - Packet going on the wire

Incoming packets destined for the local system: Prerouting --> Input

Incoming packets destined to another host: Prerouting --> Foward --> Postrouting

Locally generated packets: Output --> Postrouting

Rules

Commands to manipulate network traffic.

Each rule in the chain is queried in order - if the packet does not match the next rule is examined.

Each rule had a matching component and a Target component (action)

List Rules

iptables -S

List Rules in the format used to add them

iptables -L --line-numbers

Add a rule above an existing

iptables -I INPUT [number] <rest of -L syntax>