Early Review of draft-ietf-6man-ipv6-neighbor-discovery-yang-02
review-ietf-6man-ipv6-neighbor-discovery-yang-02-yangdoctors-early-aries-2026-02-22-00

1 module in this draft:
- ietf-ipv6-nd@2025-10-20.yang

YANG compiler errors or warnings (pyang 2.7.1, yanglint 4.2.2)
- No compiler errors or warnings

Summary:
--------------------
This is a well-scoped module and almost ready, however a few items need
addressing.

Draft:
--------------------
- Section 2.1 says `redirect` "enables the sending and processing of Redirect
  messages" but the leaf description says only "sending"
- RFC 4941 is in Normative References but only cited in the informative
  Appendix B table.  Suggest moving to Informative References.
- draft-ietf-intarea-arp-yang-model is in Normative References but only cited
  in the Introduction for background context.  Suggest moving to Informative
  References.
- Nit: malformed mailto URI in contact block: `<mailto: 6man@ietf.org>` should
  be `<mailto:6man@ietf.org>`.  Same issue in the module contact statement.

YANG Module
--------------------
- Nit: revision description "Init revision" is informal; use "Initial version."
- `units` are inconsistent throughout.  `stale-timeout` uses "second",
  `reachable-time` uses "millisecond", while `ns-interval` and `age` use
  "milliseconds".  All should use the plural form; RFC 8344 (ietf-ip) uses
  "milliseconds" consistently.  Additionally, is `stale-timeout` intentionally
  in seconds while all other timers are in milliseconds?
- `dynamic-discovery`: default "true" - what is the RFC 4861 basis for this
  default?  Address resolution is a fundamental protocol mechanism, not a
  configurable parameter with a defined default.
- `nud`: same question as above.  RFC 4861 Section 7.3 specifies NUD as
  required behavior.  Basis for this default?
- `redirect`: default "false" - RFC 4861 Section 8.1 states routers SHOULD
  send redirects.  Basis for the default?
- `reachable-time`: reference "RFC4861 - ReachableTime" is not a section
  citation.  This leaf models BaseReachableTime (Section 6.3.2; default
  30,000 ms per Section 10 REACHABLE_TIME); RFC 4861 defines no maximum for
  this variable - the range "0..3600000" is the cap on the distinct
  AdvReachableTime RA wire field (Section 6.2.1).  Cite Section 6.3.2,
  document the range rationale, and add `default "30000"`.
- `ns-interval`: reference cites Section 7.3.3; RetransTimer is defined in
  Section 6.3.2 (default 1,000 ms per Section 10 RETRANS_TIMER).  Update
  reference, add `default "1000"`, and add a minimum range constraint -
  a value of 0 would cause an NS flood it seems?
- `stale-timeout` (global and per-interface): not an RFC 4861 parameter;
  document the precedence between global and per-interface values.
- `proxy-na/inter-vlan-proxy` and `/all-proxy`: no `reference` statement;
  add RFC 4861 Section 7.2.8.  `inter-vlan-proxy` has no RFC 4861 basis;
  Is this implementation-specific?
- `enhanced-dad/enable`: no `reference` statement; add RFC 7527 Section 3.
- `enhanced-dad/enhanced-dad-auto-resolve`: no `reference` statement; add
  RFC 7527 Section 4.  Leaf name is redundant under `enhanced-dad`; prefer
  `auto-resolve`.
- All ten statistics leaves use `yang:counter32`; change to `yang:counter64`
  for consistency with RFC 8343 (ietf-interfaces) which this module augments.
- `age` augments `ip:neighbor` which covers both dynamic and static entries;
  for static entries, age is semantically undefined.  Add a `when` condition
  (e.g., `when "../ip:origin = 'dynamic'";`) or document the behavior.
  Reference Section 5.1 is imprecise; Section 7.3.2 or 7.3.3 is better.

Example Validated Instance Data:
--------------------
```
{
  "ietf-interfaces:interfaces": {
    "interface": [
      {
        "name": "eth0",
        "type": "iana-if-type:ethernetCsmacd",
        "admin-status": "up",
        "oper-status": "up",
        "if-index": 512,
        "statistics": {
          "discontinuity-time": "2026-02-21T16:00:00-08:00"
        },
        "ietf-ip:ipv6": {
          "enabled": true,
          "forwarding": true,
          "neighbor": [
            {
              "ip": "2001:db8:100::1a",
              "link-layer-address": "50:54:00:b3:4f:4a",
              "ietf-ipv6-nd:age": 600
            }
          ],
          "ietf-ipv6-nd:nd": {
            "dynamic-discovery": true,
            "nud": true,
            "reachable-time": 30000,
            "ns-interval": 1000,
            "stale-timeout": 600,
            "redirect": false,
            "proxy-na": {
              "inter-vlan-proxy": false,
              "all-proxy": false
            },
            "enhanced-dad": {
              "enable": false,
              "enhanced-dad-auto-resolve": false
            },
            "statistics": {
              "in-ns-pkts": 542321,
              "in-na-pkts": 5121,
              "in-rs-pkts": 789121,
              "in-ra-pkts": 12789532,
              "in-redirect-pkts": 0,
              "out-ns-pkts": 8343,
              "out-na-pkts": 9820934,
              "out-rs-pkts": 789243,
              "out-ra-pkts": 89032423,
              "out-redirect-pkts": 0
            }
          }
        }
      }
    ]
  },
  "ietf-ipv6-nd:nd": {
    "stale-timeout": 10000
  }
}
```