3.9 KiB
Firewall Rule Engine
Overview
Build a firewall rule parser, generator, and validator written in V (Vlang) that reads existing iptables and nftables rulesets, detects conflicts and redundancies, validates rule syntax, suggests optimizations, and generates hardened rulesets. This project introduces V—an extremely new compiled language with C-like performance and Python-like simplicity—while teaching the internals of Linux firewall configuration, rule evaluation order, and network filtering logic.
Step-by-Step Instructions
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Learn V language fundamentals and firewall concepts by working through V's documentation (simple syntax, compiles to C, no null, no undefined behavior) while studying iptables and nftables rule structure. Understand chains (INPUT, OUTPUT, FORWARD), tables (filter, nat, mangle), targets (ACCEPT, DROP, REJECT, LOG), and match criteria (source/destination IP, port, protocol, interface, state).
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Build the iptables rule parser that reads iptables-save output format and parses each rule into a structured representation: table, chain, protocol, source/destination addresses and ports, match extensions (state, conntrack, multiport, limit), target action, and any logging options. Handle all common match modules and special syntax (negation with !, ranges, CIDR notation).
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Add nftables rule parsing for the modern Linux firewall format, handling nftables list ruleset output with its different syntax: table and chain declarations, rule expressions with matches and statements, sets and maps, and verdict statements (accept, drop, reject, queue, continue). Map nftables concepts to the same internal representation used for iptables.
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Implement conflict detection that identifies problematic rule combinations: rules that can never match because an earlier rule handles all their traffic (shadowed rules), rules with contradictory criteria, duplicate rules, and rules that together create unintended allow/deny behavior. For each detected conflict, explain which rules conflict and why.
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Build the rule optimizer that suggests improvements: consolidate multiple rules into multiport matches, replace individual IP rules with CIDR ranges where possible, reorder rules to put high-traffic matches first (performance optimization), remove redundant rules that are subsets of other rules, and suggest rate limiting for exposed services.
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Create the hardened ruleset generator that produces a security-focused ruleset following best practices: default deny policy, explicit allow only for required services, loopback traffic allowed, established/related connections tracked, ICMP rate limited, logging for dropped packets, and anti-spoofing rules. Output in both iptables-restore and nftables format.
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Build an interactive CLI with commands for loading rulesets from files or live system, displaying rules in a human-readable table format, running conflict analysis, generating optimization suggestions, exporting hardened rulesets, and diffing two rulesets to show changes. Include colored output highlighting issues by severity.
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Write documentation covering iptables vs nftables comparison, rule evaluation order and why it matters for security, common firewall misconfigurations that lead to breaches, and how to test firewall rules safely. Include V language learning notes explaining the language choice and experience.
Key Concepts to Learn
- Linux firewall architecture (netfilter, iptables, nftables)
- Rule evaluation order and chain traversal
- Network filtering criteria and match modules
- Conflict detection algorithms
- V language (Vlang) compilation and syntax
- CLI application design
- Firewall hardening best practices
Deliverables
- iptables-save format parser
- nftables ruleset parser
- Conflict and redundancy detection engine
- Rule optimization suggestions
- Hardened ruleset generator (iptables + nftables formats)
- Interactive CLI with colored output and diffing