sands-lab/nika/dns-fault-skill

DNS Server-Side Faults

What These Faults Mean

• dns_record_error: the DNS server answers, but the record points to an IP the topology never declared.
• dns_service_down: the DNS daemon (named) is absent or not listening on port 53, so the server cannot answer queries.
• dns_port_blocked: the daemon is alive but nft/iptables drops port 53 traffic.
• dns_lookup_latency: a tc qdisc (netem delay or tbf) on the DNS server's egress adds large per-query latency while record/listener/firewall all look healthy.

Exit conditions

• If only one host's /etc/resolv.conf differs from peers and the DNS server itself is healthy, exit to host-ip-skill and submit host_incorrect_dns there. That RCA is NOT owned by this skill.
• If dhcpd.conf on the DHCP server pushes the wrong nameserver and affected hosts show that exact wrong resolver, exit to dhcp-fault-skill for dhcp_spoofed_dns.

Guardrails

• Do not call dns_service_down from query timeout alone; the timeout could be a firewall block or a qdisc delay. Check process, listener, AND firewall before naming dns_service_down.
• dns_lookup_latency needs the actual qdisc evidence on the DNS server's egress interface. High latency alone is not a fingerprint.
• One healthy client does not clear a server-side DNS fault.