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Your router’s device list and a network scan can disagree because they may be reporting different kinds of evidence. A DHCP list can show devices that received an address from the router, while a scan reports devices that answered particular discovery probes from a particular network location. Neither view is automatically a complete, real-time inventory, and an unfamiliar entry alone does not prove that an unauthorized device is connected.
What each view is actually showing
| What to compare | Router interface | Network scan |
|---|---|---|
| Evidence source | May show DHCP leases, active wireless stations, ARP entries, or a combined network map. Check the page’s label and fields; router interfaces vary. [TP-Link TL-WR902AC V3 user guide] | Reports responses to the discovery probes the scanner used, which can include ICMP, TCP, UDP, ARP, or IPv6 Neighbor Discovery. [Nmap host discovery documentation] |
| Time behavior | A DHCP entry can represent an address allocation and lease, not necessarily traffic at the instant you open the page. Refresh behavior and status indicators depend on the router model. [TP-Link TL-WR902AC V3 user guide] | Generally reflects responses received during the scan window. Filtering or a device’s response behavior can affect what appears. [Nmap host discovery documentation] |
| Network visibility | The router may have records from its own services or interfaces. Enterprise discovery systems may also query router ARP caches and DHCP servers, but this does not mean every consumer router’s device page does so. [Microsoft Configuration Manager discovery methods] | The scanning device’s subnet, routes, isolation settings, and probes influence which devices it can discover. [Nmap host discovery documentation; Nmap host discovery techniques] |
| Identity confidence | A client name and MAC address may be listed, but a name or label is not proof of who owns the device. [TP-Link TL-WR902AC V3 user guide] | A response shows that an address was reachable by that discovery method; it does not establish who owns the responding device. [Nmap host discovery documentation] |
For example, TP-Link’s TL-WR902AC V3 guide describes a DHCP Client List with a client name, MAC address, assigned IP address, and lease time. That is a useful record of DHCP allocations for that model, not a definition of what every router’s “connected devices” panel contains. [TP-Link TL-WR902AC V3 user guide]
Why a device can appear in one place but not the other
A router list may show a lease rather than a live connection
DHCP assigns network settings to clients and records their leases. A device can therefore remain in a DHCP list even when it is not actively sending traffic at the moment you check. Other router pages may show active wireless stations, ARP entries, or a combined map instead. Look for the exact page name, lease time, and any connection-status field before treating the list as a live headcount. [TP-Link TL-WR902AC V3 user guide]
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsA scan can miss a device that filters probes
A network scan is a method, not an oracle. Nmap’s host discovery can use different probe types, and a host may answer one kind but ignore another. Firewalls can drop probes or replies, so a device can be present yet absent from a scan’s results. The scan’s options and permissions also affect which discovery methods it can use. [Nmap host discovery documentation]
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Local-link discovery differs from discovery across a router
On local Ethernet, Nmap normally uses ARP for IPv4 or Neighbor Discovery for IPv6. Nmap notes that ARP is often more effective than IP-based ping on the local link because a device may block ping while still needing to communicate on that network. ARP is not a general way to discover devices across routed boundaries. [Nmap host discovery documentation; Nmap host discovery techniques; Apple networking documentation on packet routing and delivery]
The scan may run from a different network segment
A scan launched from guest Wi-Fi, an isolated wireless segment, a separate VLAN, or another routed subnet may not see the same local-link traffic as a device on the main LAN. This depends on the network’s configuration; it does not mean every router isolates clients by default. Check where the scanning device is connected before comparing its results with the router’s broader records. [Nmap host discovery documentation; Nmap host discovery techniques]
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An IPv4 scan is not an IPv6 inventory
If a scan covers only IPv4, it cannot establish which devices are present using IPv6. Nmap documents local IPv6 Neighbor Discovery, while the IETF’s IPv6 operational-security guidance discusses the difficulty of inventory and the value of combining sources such as traffic records, DNS, logs, and service discovery. [Nmap host discovery documentation; IETF RFC 9099]
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A scan can use records beyond the router page you checked
Discovery systems can combine sources. Microsoft Configuration Manager, for example, documents querying router ARP caches and DHCP servers, then sending ICMP echo requests to devices it finds. That illustrates why an address may be discoverable through one inventory method but absent from a particular router panel; it does not describe the behavior of every consumer router. [Microsoft Configuration Manager discovery methods]
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How to compare the two lists reliably
- Identify the router page. Record its exact name and fields. Determine whether it is a DHCP client list with lease information, a live wireless-station list, an ARP table, or a combined network map. The fields and refresh behavior are model-specific. [TP-Link TL-WR902AC V3 user guide]
- Run the scan from the network you mean to check. Connect the scanning device to the same LAN or Wi-Fi segment, and note whether it is on guest Wi-Fi or a separate VLAN. Local-link ARP and Neighbor Discovery apply to local-link discovery, not across routed boundaries. [Nmap host discovery documentation; Nmap host discovery techniques]
- Compare results taken close together in time. Refresh the router page if it offers that option, then note the scan time. Compare IP and MAC addresses where available, along with lease or connection status. A name alone may not identify the device.
- Check the scan’s method and IP version. If an expected device is missing, check whether the scan used local ARP or IPv6 Neighbor Discovery, whether the target might filter probes, and whether IPv6 was included. [Nmap host discovery documentation; IETF RFC 9099]
- Identify an unfamiliar address before acting. Check network settings on your own devices and compare their addresses with the router’s records and known device activity. If an entry remains unknown, consult the router maker’s model-specific instructions before blocking it or changing Wi-Fi credentials; there is no single safe procedure that applies to every router.
How to interpret an unfamiliar entry
Treat a new address as an unresolved identification question, not a verdict about unauthorized access. A scanner’s response establishes reachability by a particular method; a router’s DHCP entry establishes an allocation record, and neither alone identifies the owner. The cited discovery documentation explains how devices are found, not how to diagnose malicious access. [Nmap host discovery documentation; TP-Link TL-WR902AC V3 user guide]
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