---
title: "Rescan a host"
method: POST
path: "/api/v1/hosts/{id}/rescan"
tags: ["Hosts"]
---

# Rescan a host

`POST /api/v1/hosts/{id}/rescan`

Starts a one-shot scan of this host's addresses and nothing else, answering
"is this host still there, and is its data current?" without sweeping the
whole subnet.

The scan runs on the daemon that last discovered this host — evidence it can
reach the address — and only if that daemon still has an interface on a
subnet containing one of the host's IPs. That constraint is what lets the
daemon ARP the target rather than fall back to a TCP probe, which would
report a live but firewalled host as unresponsive. When it can't be met the
request is refused with the specific reason rather than run at lower fidelity.

Returns the session, which streams progress over `/api/v1/discovery/stream`
like any other scan. A `Queued` phase means the daemon is busy; it will start
when the running scan finishes.

## Path parameters

- `id` string, uuid, required

## Response `200`

Rescan session started

- ApiResponseDiscoveryUpdatePayload
  - `data` object — Progress update from daemon to server during discovery
    - `daemon_id` string, uuid, required
    - `discovery_id` string, uuid, nullable — The discovery configuration this session belongs to. Always enriched server-side; daemons do not send this field.
    - `discovery_type` union, required
      - object
        - `host_id` string, uuid, required
        - `type` 'SelfReport', required
      - object
        - `host_naming_fallback` 'Ip' | 'BestService', required
        - `snmp_credentials` object — SNMP credentials for querying devices during discovery Server builds this mapping before initiating discovery
        - `subnet_ids` string[], nullable, required
        - `type` 'Network', required
      - object
        - `host_id` string, uuid, required
        - `host_naming_fallback` 'Ip' | 'BestService', required
        - `type` 'Docker', required
      - object — A one-shot verification of a single host: re-check the addresses and ports already recorded for it, rather than sweeping a subnet. Created by the server only (never via the API) and deleted once its session reaches a terminal phase, so it is not a discovery configuration anyone owns or sees in their scan list.
        - `host_id` string, uuid, required — ID of the host that the daemon is running on — same meaning as every other variant. The host being rescanned is `target_host_id`.
        - `ips` string[], required — Addresses to scan on that host.
        - `ports` PortType[] — Ports already known on that host, re-checked to confirm they are still open. Scanned in addition to the standard discovery set, so a rescan also surfaces newly-opened services.
          - `number` integer, required
          - `protocol` 'Udp' | 'Tcp', required
          - `type` string — Auto-derived from number+protocol; optional on create
        - `settings` RescanSettings — Scan settings that apply to a single-host rescan. Deliberately narrower than [`ScanSettings`]: a rescan verifies a known host against a known port set, so the full-scan mechanism (`is_full_scan`, `full_scan_interval`) must not be expressible — promoting a rescan to a 65,535-port sweep defeats the feature. The remaining omissions are settings that cannot bind on a one-or-two address target.
          - `arp_retries` integer, nullable — ARP retry rounds. Matters more here than in a sweep: for a rescan, "did it answer" is the entire answer, so a missed round reads as a dead host.
          - `port_scan_batch_size` integer, nullable — Ports scanned concurrently per host.
          - `probe_raw_socket_ports` boolean — Whether to probe raw-socket ports 9100-9107. Correctness-affecting: with this off the scanner drops those ports from its results, so a printer's known JetDirect port would look like it had disappeared.
          - `scan_rate_pps` integer, nullable — Port scan probes per second. Operators lower this for fragile devices or noisy IDS, and a rescan must respect that as much as a discovery does.
          - `use_npcap_arp` boolean — On Windows, use Npcap broadcast ARP instead of SendARP.
        - `target_host_id` string, uuid, required — The host being rescanned.
        - `type` 'Rescan', required
      - object
        - `host_id` string, uuid, required — ID of the host that the daemon is running on
        - `host_naming_fallback` 'Ip' | 'BestService', required
        - `scan_settings` ScanSettings — Scan performance settings. Lives on the discovery entity. Numeric fields are `Option<T>` — `None` means "use daemon default". The daemon unwraps with defaults at point of use.
          - `arp_rate_pps` integer, nullable — ARP packets per second (default: 50)
          - `arp_retries` integer, nullable — ARP retry rounds for non-responsive targets (default: 2 = 3 total attempts)
          - `arp_scan_cutoff` integer, nullable — ARP scan cutoff prefix. Interfaced subnets larger than this prefix are truncated to this many IPs. Default: 15 (= /15, ~131K IPs). Lower values scan more IPs — increase arp_rate_pps accordingly.
          - `full_scan_interval` integer, nullable — Run a full 65k port scan every N scans. Other scans use a light port set. Default: 3. Value of 0 means never full scan. Value of 1 means every scan is full.
          - `is_full_scan` boolean — Whether this specific scan run should do a full 65k port scan. Set by the server before dispatching to the daemon — not user-configurable.
          - `max_discovery_duration` integer, nullable — Hard ceiling on how long a single discovery run may take, in seconds (default: 21600 = 6h). When hit, the run force-completes and any hosts still queued are left un-scanned until the next run. Raise this for very large networks that legitimately need more than the default window.
          - `port_scan_batch_size` integer, nullable — Ports scanned concurrently per host (default: 200, clamped 16-1000)
          - `probe_raw_socket_ports` boolean — Whether to probe raw-socket ports 9100-9107 (default: false). Disabled by default to prevent ghost printing on JetDirect printers.
          - `scan_rate_pps` integer, nullable — Port scan probes per second (default: 500)
          - `use_npcap_arp` boolean — On Windows, use Npcap broadcast ARP instead of SendARP (default: false)
        - `subnet_ids` string[], nullable, required — Subnets to scan. None = scan all interfaced subnets.
        - `type` 'Unified', required
    - `error` string, nullable
    - `estimated_remaining_secs` integer, nullable
    - `finished_at` string, date-time, nullable
    - `hosts_discovered` integer, nullable
    - `network_id` string, uuid, required
    - `phase` 'AwaitingSnapshot' | 'Queued' | 'Pending' | 'Starting' | 'Started' | 'Scanning' | 'Complete' | 'Failed' | 'Cancelled', required
    - `progress` integer, required
    - `scanned` ScannedEntityIds — Canonical IDs of entities scanned in a discovery session. Populated daemon-side at terminal phase from `EntityBuffer`'s `Created` entries. Travels with the terminal `DiscoveryUpdatePayload` to the server, rides the in-memory `EntityOperation::Created` event published for the historical Discovery row (the event scope carries `Entity::Discovery` with the full struct, including `run_type::Historical { results }`), then is stripped before persisting into the historical Discovery row's JSONB (see the `SqlValue::RunType` bind_value handler in `backend/src/server/shared/storage/generic.rs`). Per-entity-service subscribers extract `results.scanned` from the in-memory event and call `DiscoveryFkUpdater::update_discovery_fks` to backfill `last_discovery_id` / `first_discovery_id` on the matched rows. Naming: `scanned_*` because the daemon scans entities — some submissions match existing rows (refresh), others insert new rows. Both populate the EntityBuffer with canonical (server-assigned) IDs.
      - `binding_ids` string[]
      - `host_ids` string[]
      - `interface_ids` string[]
      - `ip_address_ids` string[]
      - `port_ids` string[]
      - `service_ids` string[]
      - `subnet_ids` string[]
      - `vlan_ids` string[]
    - `session_id` string, uuid, required
    - `started_at` string, date-time, nullable
    - `warnings` string[] — Non-fatal warnings for a completed run (e.g. the scan hit its time limit and left hosts un-scanned). Unlike `error`, these do not mark the run failed.
  - `error` string, nullable
  - `meta` ApiMeta, required — API metadata included in all responses
    - `api_version` integer, required — API version (integer, increments on breaking changes)
    - `server_version` string, required — Server version (semver)
  - `success` boolean, required

## Other responses

- `400` — Host cannot be rescanned (never scanned, daemon gone, daemon unreachable, or daemon too old)
- `404` — Host not found

## Changes

- **2026-07-29** `49ea97c8bb7e` — 1 breaking, 1 warning
  - added `subschema #4: Rescan` to the `data/discovery_type` response property `oneOf` list for the response status `200`
  - removed the optional property `data/targeted` from the response with the `200` status
- **2026-07-28** `1be6783504b4` — 1 info
  - endpoint added

[Change history](https://skmtc.dev/scanopy/apis/scanopy-api/changes/api/v1/hosts/:id/rescan/post.md)

---

[API](https://skmtc.dev/scanopy/apis/scanopy-api.md) · [All operations](https://skmtc.dev/scanopy/apis/scanopy-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/scanopy/scanopy-api/revisions/49ea97c8bb7e/schema)