iptables vs. nftables vs. firewalld: A Comprehensive Comparison for Linux Firewalls

In the ever-evolving landscape of Linux network security, understanding the differences between traditional tools like iptables and modern alternatives like nftables and firewalld is crucial for system administrators. This blog post delves into a comparison based on architecture, features, and syntax.

Architecture Comparison

Feature	iptables	nftables	firewalld
Kernel Module	Multiple modules (ip_tables)	Single nftables module	Front-end, backend uses nftables
Protocol Support	Separate for IPv4/6 (ip6tables)	Unified IPv4/6/ARP/bridge traffic	Handles multiple protocols automatically
Rule Storage	Linear traversal of rule sets	Red-black tree-based structure	Dynamic rule management
Performance	Performance degrades with more rules	30% better rule matching efficiency	Depends on backend engine performance

Insight: With its single kernel module, nftables inherently offers better performance and scalability, managing rules more efficiently than iptables.

NAT Configuration Comparison

Traditional iptables MASQUERADE

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

Modern nftables Equivalent

nft add table ip nat
nft add chain ip nat POSTROUTING { type nat hook postrouting priority 100 \; }
nft add rule ip nat POSTROUTING oifname "eth0" masquerade

• Advantage: Automatic compatibility with IPv4 and IPv6, clear priority settings.

firewalld Rich Rule Example

firewall-cmd --permanent --zone=public --add-rich-rule='rule family=ipv4 source address=192.168.1.0/24 masquerade'

• Advantage: Dynamic updates and policy grouping via zones.

Feature Evolution

1. Rule Tracing:
   • nftables: Built-in trace for real-time rule matching monitoring.

   nft monitor trace

• iptables: Requires TRACE target and xtables-monitor.

1. Batch Operations:
   • iptables: Needs individual commands for each rule.
   • nftables: Supports set operations for efficiency.

   nft add rule filter input tcp dport {22,80} accept

1. IPv6 Support:
   • iptables: Requires separate rules with ip6tables.
   • nftables: Uses inet family for handling dual-stack traffic effortlessly.

Migration Practices

1. Conversion Tools:

   • Use iptables-translate to convert existing iptables rules to nftables syntax automatically.

2. Hybrid Operation:

   • Implement iptables-nft for a smooth transition.

3. Performance Tuning:

   • With nftables, enable JIT compilation for enhanced performance:

   nft set ruleset optimize=full

Conclusion: For new setups, nftables is highly recommended due to its superior performance, lower memory usage, and better manageability. Existing iptables rules can be migrated using available tools, making the transition less daunting. Firewalld, on the other hand, is ideal for environments needing dynamic firewall management with user-friendly interaction through zones.

References:

• Netfilter's nftables Documentation
• Fedora's firewalld Introduction
• Performance Comparison of iptables and nftables
• OpenSUSE's Guide to nftables

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