147 lines
4.8 KiB
Markdown
147 lines
4.8 KiB
Markdown
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# DNS Server Algorithm & Flowchart
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This document outlines the algorithm and flowchart for a DNS server implementation compliant with RFC 1035 (DNS) and RFC 4034 (DNSSEC).
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---
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## ✅ Server Algorithm
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### 1. Server Initialization
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1. Load configuration from environment variables.
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2. Initialize the logging system.
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3. Create SQLite database connection and initialize schema.
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4. Initialize cache with NS records.
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5. Start periodic cache cleanup task (every 5 minutes).
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6. Bind and listen on UDP and TCP sockets.
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### 2. Query Handling Flow
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#### Upon Receiving a DNS Query:
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1. Validate DNS query packet.
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2. Parse header and extract domain name and query type.
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3. If query type is `DNSKEY` or `DS`, return signed records.
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4. Check DNS cache:
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- If **hit**, build and return response.
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- If **miss**, lookup in database:
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- If found, respond and cache it.
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- If not found:
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- If authoritative, return `NXDOMAIN`.
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- Else, forward to upstream resolvers.
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5. Add DNSSEC signatures if applicable.
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6. Send response to the client.
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### 3. DNSSEC Signing Process
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1. Load DNSSEC key from configured file.
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2. For each relevant record:
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- Generate `RRSIG`.
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- Encode signature (Base64).
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- Calculate key tag and signature expiration.
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3. Add `RRSIG` to the answer section.
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4. Include `DNSKEY` in the authority section if needed.
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### 4. Response Generation Logic
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1. Construct response header:
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- Set QR flag and response code.
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- Include Authoritative Answer (AA) if authoritative.
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2. Attach original question section.
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3. Populate:
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- **Answer** section: with resolved records.
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- **Authority** section: with NS and DS records.
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- **Additional** section: with glue records, DNSKEY if required.
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---
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## 📊 Flowchart
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Below is the visual representation of the DNS query handling logic:
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```
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+---------------------+
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| Start DNS Server |
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+---------------------+
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v
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+---------------------+
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| Receive DNS Query |
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+---------------------+
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v
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+---------------------+
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| Parse Header and |
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| Extract Domain & |
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| Query Type |
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+---------------------+
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+---------------------+
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v v
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+---------------------+ +---------------------+
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| Is Query Type | | Use Cache |
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| DNSKEY/DS? | | |
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+---------------------+ +---------------------+
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Yes | |
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v v
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+---------------------+ +---------------------+
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| Return | | Lookup in SQLite DB |
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| DNSSEC Record | | |
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+---------------------+ +---------------------+
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v
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+---------------------+
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| Is Authoritative |
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| Zone? |
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+---------------------+
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No |
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v
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+---------------------+
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| Return NXDOMAIN |
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+---------------------+
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v
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+---------------------+
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| Add GSSEC |
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+---------------------+
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v
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+---------------------+
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| Send Response |
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+---------------------+
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v
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+---------------------+
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| End |
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+---------------------+
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```
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## 🧩 Key Components
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| Component | Purpose | Details |
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|----------------|----------------------------|------------------------------------------|
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| `DnsCache` | DNS Response Cache | Thread-safe HashMap with TTL |
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| `ServerConfig` | Server Configuration | Loaded via environment variables |
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| `rusqlite` | Record Storage | SQLite database backend |
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| `tokio` | Async I/O Runtime | UDP/TCP async handlers and tasks |
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| `DNSSEC` | Secure DNS Signing | RSA-SHA256 with Base64-encoded keys |
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---
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## ⚠️ Error Handling Strategy
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- Custom `DnsError` enum via `thiserror`
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- Graceful shutdown via `SIGINT`
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- Cache cleanup every 5 minutes
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- Fallback to resolver forwarding
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- Detailed logging at every stage
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---
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