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BIND Local DNS Resolver

Problem Statement​

  • Security Challenge: Slow or unreliable public DNS causes latency and resolution failures.
  • Real-World Scenarios: External DNS rate-limits, outages, or geo-DNS inconsistencies impact content access and threat lookups.
  • Business Context: DNS instability affects browsing performance, policy enforcement, and malware categorization accuracy.

Key Benefits​

  • Desired Outcome: Fast, consistent, and locally controlled DNS for SafeSquid SWG.
  • Value Proposition: Reduce DNS lookup time and improve cache hits for repeated domains.
  • Competitive Advantage: Enterprise-grade control, auditability, and resilience versus public resolvers.

Prerequisites​

  • Client-Side Preparations: Confirm upstream DNS policy; define allowed egress for UDP/TCP 53.
  • SafeSquid-Side Setup: Plan SafeSquid to query local resolver IP.
  • System Requirements: Linux host, BIND 9.x, time synchronization (NTP) for DNSSEC validation.

Call to Action​

  1. Install BIND.
    • Debian/Ubuntu: 
      sudo apt update
      sudo apt install -y bind9 bind9-utils
    • RHEL/Rocky: 
      sudo dnf install -y bind bind-utils
    • Verification: named -v prints version.
  2. Configure named options.
    • Edit /etc/bind/named.conf.options (Debian/Ubuntu) or /etc/named.conf (RHEL): 
      options {
        directory "/var/cache/bind";
        recursion yes;
        allow-recursion { 127.0.0.1; 10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16; };
        listen-on port 53 { 127.0.0.1; 10.0.0.1; }; // replace with resolver IP
        allow-query { any; };
        dnssec-validation auto;
        auth-nxdomain no;
        minimal-responses yes;
        rate-limit {
          responses-per-second 25;
        };
      };
    • Verification: named-checkconf returns no output.
  3. Configure root hints and local zones (optional).
    • Ensure root.hints present: 
      curl -o /var/cache/bind/root.hints https://www.internic.net/domain/named.root
    • Add local overrides file named.conf.local: 
      zone "corp.local" { type forward; forwarders { 10.0.0.10; 10.0.0.11; }; };
    • Verification: named-checkzone corp.local /dev/null validates syntax.
  4. Enable and start BIND. 
    sudo systemctl enable --now bind9 || sudo systemctl enable --now named
    systemctl is-active bind9 || systemctl is-active named
    • Verification: Service shows active.
  5. Point SafeSquid to local resolver.
    • Set DNS server IP in SafeSquid SWG host (e.g., /etc/resolv.conf or system resolver config) to the BIND IP.
    • Verification: dig @127.0.0.1 example.com +stats shows ANSWER and query time.
  6. Harden resolver.
    • Enable response policy zones (RPZ) if used for threat blocking.
    • Restrict recursion to trusted subnets only.
    • Enable logging categories in named.conf: 
      logging {
        channel default_log { file "/var/log/named/default.log" versions 5 size 10m; severity info; print-time yes; };
        category resolver { default_log; };
        category security { default_log; };
      };
    • Verification: Logs rotate and record query activity.

Solution Verification​

  • Interface Checks: N/A (service daemon). Validate using CLI diagnostics.
  • Log Analysis: Review /var/log/named/default.log or journalctl -u bind9 -f for errors and query logs.
  • Performance Validation: dig @resolver-ip popular-domain.tld +noall +stats shows low query time and growing cache hit rate.
  • Screenshots: /img/supporting-services/bind-dig-stats.webp with alt text "dig output showing low latency and cache hits".

Troubleshooting Guide​

  • Common Issues & Scenarios:
    • SERVFAIL on DNSSEC domains: Missing time sync or DNSSEC trust anchors.
    • High latency: No caching, blocked egress to root/forwarders, or RRL misconfiguration.
    • Refused queries: Recursion limited to wrong subnets or listen-on mismatch.
    • Port conflicts: Another resolver binding to 53.
  • Resolution Steps:
    • Fix time: Ensure NTP sync and dnssec-validation auto.
    • Check egress: Allow UDP/TCP 53; verify root.hints or forwarders reachability.
    • Adjust ACLs: Correct allow-recursion and listen-on addresses.
    • Free port: Stop conflicting service or change BIND listen IPs.
  • Escalation Procedures:
    • Collect named-checkconf, rndc status, dig +trace outputs, logs.
    • Contact SafeSquid support with configuration snippets and diagnostics.