57 lines
3.2 KiB
Plaintext
57 lines
3.2 KiB
Plaintext
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=== W2: does a production node take a DHCPv6 reservation? ===
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Window of 2026-09-06, operator offline.
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SHORT ANSWER: the RA half works; the RESERVATION half does not, and the reason
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is structural rather than a misconfiguration.
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WHAT WORKS
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- RA is emitted on bond0.2 with AdvManagedFlag on, AdvAutonomous off,
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AdvLinkMTU 1472, AdvDefaultLifetime 0 (deliberately not a default router).
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- NetworkManager on worker0 SAW it and acted:
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dhcp6 (eno1): activation: beginning transaction (timeout in 45 seconds)
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So "ipv6.method=auto follows the managed flag" is now EVIDENCE, not
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inference. That was the open question this window set out to close.
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- kea-dhcp6 runs on both routers and receives SOLICITs on bond0.2.
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WHAT DOES NOT WORK, AND WHY
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Every DHCPv6 packet kea logs is annotated [no hwaddr info]:
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duid=[00:04:69:d9:30:64:c3:4e:...] [no hwaddr info] <- DUID-UUID (type 4)
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duid=[00:04:25:11:e0:0a:7b:c4:...] [no hwaddr info] <- DUID-UUID
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duid=[00:01:00:01:31:78:0a:ae:...] [no hwaddr info] <- DUID-LLT (type 1)
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DHCPv6 identifies a client by DUID, not by MAC. kea can sometimes DERIVE a MAC
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(its mac-sources machinery), but here it derives nothing -- including from a
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DUID-LLT, which does embed one. So `hw-address` reservations cannot match, and
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a node that solicits gets no reserved address.
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VyOS accepting `static-mapping <name> mac` is therefore necessary but NOT
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sufficient: it renders valid kea config ("hw-address": "78:55:36:08:28:fb",
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confirmed in /run/kea/kea-dhcp6.conf) that simply never matches these clients.
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The plan's assumption -- "reservations keyed on MAC, one source of truth with
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IPv4" -- does not survive contact with DHCPv6.
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OPTIONS, none free, for an attended session:
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a) Key reservations on DUID (VyOS static-mapping supports `duid`). Works, but a
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DUID is client-generated: it is a SECOND source of truth, it must be
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harvested per node, and it changes if a node is rebuilt -- which is exactly
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the "out of the box for new nodes" property we were trying to preserve.
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b) Set kea `mac-sources` explicitly and see whether any method recovers a MAC
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from these clients. Cheap to try; may simply not work for DUID-UUID.
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c) Drop reservations: hand out a dynamic range and have labctl DISCOVER the
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node's address rather than predict it. The k3s preflight (914135c) already
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refuses to write a node-ip the node does not hold, so discovery is safe --
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but the address is then not knowable before the node boots.
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d) SLAAC with no-autonomous cleared, and accept EUI-64 addresses. Stable per
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NIC and needs no server state at all, but the address is not ours to choose.
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A SECOND FINDING, unrelated and worse if unnoticed
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`service dhcpv6-server` with no listen-interface renders kea6 with
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interfaces: [ "*" ] -- a DHCPv6 server on EVERY VLAN. Observed live: kea began
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answering SOLICIT/REQUEST from an unrelated device on bond0.10 (LoT) within
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seconds of the first apply. Same family as the kea IPv4 cross-VLAN bug (ISC
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#1117) this estate already fought. Fixed by pinning
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`set service dhcpv6-server listen-interface bond0.2` plus a subnet-level
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`interface bond0.2`; both routers now render interfaces: ["bond0.2"].
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