Windows’ Alternate Configuration is an IPv4 fallback profile for a single network adapter. Windows uses DHCP first; it applies the alternate address only if DHCP cannot provide a lease. To use the feature, keep the adapter set to obtain an IP address automatically on the General tab, then enter the fallback details under Alternate Configuration.
What Alternate Configuration does
The feature lets one Ethernet or Wi-Fi adapter fall back to a predefined IPv4 configuration when it cannot obtain settings from a DHCP server. The profile can include an IP address, subnet mask, default gateway, DNS servers, and legacy WINS values. Microsoft describes DHCP as the client/server protocol that automatically supplies an IP address and related settings such as the subnet mask and default gateway: Microsoft’s DHCP overview.
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Windows attempts DHCP first. If no lease is available and you have configured a user profile, Windows uses that fallback. If neither DHCP nor an alternate profile provides an address, Windows typically assigns itself an APIPA address in the 169.254.0.0/16 range.
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Good fit: switching between DHCP and a known local network
Alternate Configuration is useful for a laptop that normally connects to an office DHCP network but sometimes needs a known static address on an isolated lab, maintenance, staging, industrial, or direct-device network. It can also help preserve local access during a DHCP outage, provided the fallback network’s addressing is known and compatible.
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Choose another approach for a permanent or simultaneous setup
- For a device that should always use one fixed address, configure a normal static address instead.
- For a predictable address on a managed network, ask the network administrator about a DHCP reservation.
- For simultaneous access to separate networks, use separate adapters or VLANs; Alternate Configuration is a fallback, not a second active address.
The fallback profile does not reproduce every setting a DHCP server can provide, such as domain suffixes, proxy settings, or classless routes.
Configure an IPv4 fallback profile
- Identify the Ethernet or Wi-Fi adapter that needs the fallback.
- Open Settings → Network & Internet → Advanced network settings → More network adapter options. In the adapter list, right-click the intended adapter and choose Properties.
- Select Internet Protocol Version 4 (TCP/IPv4), then choose Properties.
- On the General tab, leave Obtain an IP address automatically selected. Leave Obtain DNS server address automatically selected as well if that is how the normal DHCP network provides DNS.
- Open Alternate Configuration, select User configured, and enter an unused IPv4 address and the subnet mask that match the fallback network.
- Enter a default gateway only if the fallback network has a router. Leave it blank for a direct connection or a local-only network with no router.
- Enter DNS server addresses only if name resolution is needed and those servers will be reachable from the fallback network.
- Save the settings and record the adapter, fallback address, subnet, and the network scenario for which the profile is intended.
Choose an address that belongs to the fallback network’s subnet and is not already in use. A duplicate address can cause intermittent or complete connectivity failures. If you are unsure which addresses are available or which mask to use, confirm the network plan with its administrator or device documentation rather than guessing.
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Test that Windows uses the fallback
A connected DHCP server takes precedence, so testing while connected to the normal office network will not demonstrate fallback behavior. A small unmanaged Ethernet switch can help create a test network with no DHCP server: connect the computer and a test device to the switch, without connecting a router or DHCP-enabled network. A direct Ethernet connection to a test device can also work if both sides support the link.
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- On the normal DHCP network, open Command Prompt and run
ipconfig /all. Confirm the adapter is receiving its expected DHCP configuration. - Move the computer to the isolated switch or direct test connection. Make sure no DHCP server is present on that network.
- In Command Prompt, run
ipconfig /release, thenipconfig /renew. Allow the DHCP attempt to fail or time out. - Run
ipconfig /allagain. Check that the adapter shows the alternate IPv4 address, subnet mask, and any gateway or DNS values you configured. - Use
pingto test a peer on the same subnet or the configured gateway, if there is one. If you configured alternate DNS, usenslookupto check name resolution. - Reconnect to the normal DHCP network, run
ipconfig /renew, and verify withipconfig /allthat the adapter has returned to its DHCP-provided configuration.
Troubleshoot an unexpected address or failed connection
Windows still shows a DHCP address
If a DHCP server responds, Windows is expected to use its lease rather than the alternate profile. Repeat the test on a network with no DHCP server and confirm you edited the adapter that is actually connected.
The address begins with 169.254
A 169.254.x.x address indicates that Windows used APIPA instead of your custom fallback. Reopen the IPv4 properties for the correct adapter and check that User configured is selected on the Alternate Configuration tab. Also confirm that the General tab still has automatic IP addressing selected.
The local device is unreachable
Check that the fallback address is unused and belongs to the same subnet as the peer, using a compatible subnet mask. An incorrect subnet or duplicate address can prevent local communication. If a router is not part of the fallback network, remove the default gateway; an incorrect gateway can prevent traffic from reaching other subnets.
IP connections work, but names do not
DNS must be reachable on the fallback network. Test the destination by IP address first. If that works but name lookups fail, verify the configured DNS server address and whether that server is reachable from the fallback network.
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