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[dns] Kea: multi-IP DHCP option 6 (10.0.10, 10.0.20) + TSIG-signed DDNS (WS E)

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Workstream E of the DNS hardening push. Two independent pfSense-side
changes to eliminate single-point DNS failures and the unauthenticated
RFC 2136 update vector.

Part 1 — Multi-IP DHCP option 6
- Before: clients on 10.0.10/24 got only 10.0.10.1; clients on 10.0.20/24
  got only 10.0.20.1. Internal resolver outage == cluster-wide DNS dark.
- After:
  - 10.0.10/24 -> [10.0.10.1, 94.140.14.14]
  - 10.0.20/24 -> [10.0.20.1, 94.140.14.14]
- 192.168.1/24 deliberately untouched (served by TP-Link AP, not pfSense
  Kea — pfSense WAN DHCP is disabled); already ships [192.168.1.2,
  94.140.14.14] so the end state is consistent across all three subnets.
- Applied via PHP: set $cfg['dhcpd']['lan']['dnsserver'] and
  $cfg['dhcpd']['opt1']['dnsserver'] as arrays. pfSense's
  services_kea4_configure() implodes the array into "data: a, b" on the
  "domain-name-servers" option-data entry (services.inc L1214).
- Verified:
  - DevVM (10.0.10.10) resolv.conf shows "nameserver 10.0.10.1" +
    "nameserver 94.140.14.14" after networkd renew.
  - k8s-node1 (10.0.20.101) same after networkctl reload + systemd-resolved
    restart.
  - Fallback drill on k8s-node1: `ip route add blackhole 10.0.20.1/32`;
    dig @10.0.20.1 google.com -> "no servers could be reached"; dig
    @94.140.14.14 google.com -> 216.58.204.110; system resolver
    (getent hosts) succeeds via the fallback IP. Blackhole route removed.

Part 2 — TSIG-signed Kea DHCP-DDNS
- Before: /usr/local/etc/kea/kea-dhcp-ddns.conf had `tsig-keys: []` and
  Technitium's viktorbarzin.lan zone had update=Deny. Unauthenticated
  update vector was latent (DDNS wiring in Kea DHCP4 is actually off
  today — "DDNS: disabled" in dhcpd.log) but would activate as soon as
  anyone turned on ddnsupdate on LAN/OPT1.
- Generated HMAC-SHA256 secret, base64-encoded 32 random bytes.
- Stored in Vault: secret/viktor/kea_ddns_tsig_secret (version 27).
- Created TSIG key "kea-ddns" on primary/secondary/tertiary Technitium
  instances via /api/settings/set (tsigKeys[]).
- Updated kea-dhcp-ddns.conf on pfSense with
  tsig-keys[]={name: "kea-ddns", algorithm: "HMAC-SHA256", secret: …}
  and key-name: kea-ddns on each forward-ddns / reverse-ddns domain.
  Pre-change backup at /usr/local/etc/kea/kea-dhcp-ddns.conf.2026-04-19-pre-tsig.
- Configured viktorbarzin.lan + 10.0.10.in-addr.arpa +
  20.0.10.in-addr.arpa + 1.168.192.in-addr.arpa on Technitium primary:
  - update = UseSpecifiedNetworkACL
  - updateNetworkACL = [10.0.20.1, 10.0.10.1, 192.168.1.2]
  - updateSecurityPolicies = [{tsigKeyName: kea-ddns,
                               domain: "*.<zone>", allowedTypes: [ANY]}]
  Technitium requires BOTH a source-IP match AND a valid TSIG signature.
- Verified TSIG end-to-end:
  - Signed A-record update from pfSense -> "successfully processed",
    dig returns 10.99.99.99 (log: "TSIG KeyName: kea-ddns; TSIG Algo:
    hmac-sha256; TSIG Error: NoError; RCODE: NoError").
  - Signed PTR update same zone pattern -> dig -x returns tsig-test
    FQDN.
  - Unsigned update from pfSense IP (in ACL) -> "update failed:
    REFUSED" (log: "refused a zone UPDATE request [...] due to Dynamic
    Updates Security Policy").
  - Test records cleaned up via signed nsupdate.

Safety
- pfSense config backup: /cf/conf/config.xml.2026-04-19-pre-kea-multi-ip
  (145898 bytes, pre-change snapshot — keep 30d).
- DDNS config backup: /usr/local/etc/kea/kea-dhcp-ddns.conf.2026-04-19-pre-tsig.
- TSIG secret lives only in Vault + in config.xml/kea-dhcp-ddns.conf on
  pfSense; not committed to git.

Docs
- architecture/dns.md: zone dynamic-updates section records the TSIG
  policy; Incident History gets a WS E entry.
- architecture/networking.md: DHCP Coverage table now shows the DNS
  option 6 values per subnet; pfSense block notes the TSIG-signed DDNS
  and config backup path.
- runbooks/pfsense-unbound.md: new "Kea DHCP-DDNS TSIG" section covers
  key rotation, emergency bypass, and enforcement-verification.

Closes: code-o6j

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Viktor Barzin 2026-04-19 16:12:23 +00:00
parent a05d63eefb
commit f6685a23a9
3 changed files with 100 additions and 15 deletions
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9
docs/architecture/dns.md
View file

@ -1,6 +1,6 @@
# DNS Architecture
Last updated: 2026-04-19 (WS C — NodeLocal DNSCache deployed; WS D — pfSense Unbound replaces dnsmasq)
Last updated: 2026-04-19 (WS C — NodeLocal DNSCache deployed; WS D — pfSense Unbound replaces dnsmasq; WS E — Kea multi-IP DHCP option 6 + TSIG-signed DDNS)
## Overview
@ -212,7 +212,7 @@ All three pods share the `dns-server=true` label, so the DNS LoadBalancer (10.0.
| `0.168.192.in-addr.arpa` | Primary | PTR | Reverse DNS for Valchedrym site |
| `emrsn.org` | Primary (stub) | — | Returns NXDOMAIN locally (avoids 27K+ daily corporate query floods) |
**Dynamic updates**: Enabled via `UseSpecifiedNetworkACL` from pfSense IPs (10.0.20.1, 10.0.10.1, 192.168.1.2) for Kea DDNS RFC 2136 updates.
**Dynamic updates**: Enabled via `UseSpecifiedNetworkACL` from pfSense IPs (10.0.20.1, 10.0.10.1, 192.168.1.2) **AND require a valid TSIG signature** on `viktorbarzin.lan`, `10.0.10.in-addr.arpa`, `20.0.10.in-addr.arpa`, `1.168.192.in-addr.arpa`. Policy: `updateSecurityPolicies = [{tsigKeyName: "kea-ddns", domain: "*.<zone>", allowedTypes: ["ANY"]}]`. Unsigned updates from the allowlisted pfSense source IPs are refused ("Dynamic Updates Security Policy"). TSIG key `kea-ddns` (HMAC-SHA256) present on primary/secondary/tertiary; secret in Vault `secret/viktor/kea_ddns_tsig_secret`. Applied 2026-04-19 (WS E, bd `code-o6j`).
### Resolver Settings
@ -375,8 +375,8 @@ The Cloudflare tunnel uses a **wildcard rule** (`*.viktorbarzin.me → Traefik`)
Devices get automatic DNS registration without manual intervention. See [networking.md § IPAM & DNS Auto-Registration](networking.md#ipam--dns-auto-registration) for the full data flow diagram.
Summary:
1. **Kea DHCP** on pfSense assigns IP (53 reservations across 3 subnets)
2. **Kea DDNS** sends RFC 2136 dynamic update to Technitium (A + PTR records) — immediate
1. **Kea DHCP** on pfSense assigns IP (53 reservations across 3 subnets). DHCP option 6 (DNS servers) is pushed with two IPs per internal subnet: internal resolver + AdGuard public fallback (`94.140.14.14`) — clients survive an internal DNS outage.
2. **Kea DDNS** sends **TSIG-signed** RFC 2136 dynamic update to Technitium (A + PTR records) — immediate. Key `kea-ddns` (HMAC-SHA256); Technitium enforces both source-IP ACL and TSIG signature on `viktorbarzin.lan` + reverse zones.
3. **phpipam-pfsense-import** CronJob (5min) pulls Kea leases + ARP table into phpIPAM
4. **phpipam-dns-sync** CronJob (15min) pushes named phpIPAM hosts → Technitium A + PTR, pulls Technitium PTR → phpIPAM hostnames
@ -502,6 +502,7 @@ For external `.viktorbarzin.me` records:
- **2026-04-14 (SEV1)**: NFS `fsid=0` caused Technitium primary data loss on restart. Fixed by migrating all 3 instances to `proxmox-lvm-encrypted`, adding zone-sync CronJob (30min AXFR). See [post-mortem](../post-mortems/2026-04-14-nfs-fsid0-dns-vault-outage.md).
- **2026-04-19 (hardening, not outage)**: Workstream D — pfSense Unbound replaces dnsmasq as the pfSense DNS service. Unbound AXFR-slaves `viktorbarzin.lan` from Technitium so LAN-side resolution survives a full K8s outage. WAN NAT rdr `192.168.1.2:53 → 10.0.20.201` removed (Unbound listens on WAN directly). DoT upstream via Cloudflare. See `docs/runbooks/pfsense-unbound.md` and bd `code-k0d`.
- **2026-04-19 (hardening, not outage)**: Workstream E — Kea DHCP now pushes TWO DNS IPs (internal + AdGuard public fallback `94.140.14.14`) via option 6 to the internal subnets (10.0.10/24, 10.0.20/24); 192.168.1/24 was already dual-IP (served by TP-Link). Kea DHCP-DDNS now TSIG-signs its RFC 2136 updates (key `kea-ddns`, HMAC-SHA256) and the Technitium zones require both source-IP ACL AND TSIG signature. See `docs/runbooks/pfsense-unbound.md` § "Kea DHCP-DDNS TSIG" and bd `code-o6j`.
## Related