When connected to a corporate VPN, Windows systems often exhibit a frustrating behavior where local network shares become inaccessible with the error "The user name could not be found". This occurs because Windows prioritizes the VPN-assigned DNS servers over your local domain controllers, creating a namespace resolution conflict.

The issue manifests when:

1. VPN connection modifies the network adapter's DNS settings
2. The DNS suffix search order gets altered
3. NetBIOS name resolution fails due to network segmentation

Test connectivity with these commands:

nslookup server.domain.local  # Should resolve to local DC
nslookup server              # May fail when VPN connected
ping -a 192.168.1.100        # Verify reverse lookup

Method 1: Force Local DNS Precedence
Modify the VPN adapter's metric to deprioritize it:

netsh interface ipv4 set interface "VPN Connection" metric=5000

Method 2: Registry-Based DNS Suffix Control
Add local domain suffixes to the search list:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"SearchList"="domain.local,corp.domain.com"

Create a script to toggle settings when VPN connects:

# VPN connection event handler
Register-EngineEvent -SourceIdentifier VPN.Connected -Action {
    Set-DnsClientGlobalSetting -SuffixSearchList @("domain.local","corp.domain.com")
    Set-DnsClient -InterfaceAlias "Ethernet" -ConnectionSpecificSuffix "domain.local"
}

For domain-joined machines, implement Group Policy:

1. Computer Configuration > Policies > Administrative Templates > Network > DNS Client
2. Enable "Primary DNS Suffix Devolution" and "Connection-Specific DNS Suffix"
3. Configure "DNS Suffix Search List" with your local domain

When connected to a VPN, Windows often prioritizes the VPN provider's DNS settings over your local Active Directory DNS. This creates a name resolution conflict where:

• Direct IP access works (\\192.168.1.100\share)
• FQDN access works (\\server.domain.local\share)
• But NETBIOS/short names fail (\\fileserver\share)

Test your current resolution behavior with these commands:

nslookup fileserver        # Should return local IP
nslookup fileserver 8.8.8.8 # Forces public DNS check
ping -a 192.168.1.100      # Verify reverse lookup

Modify the network adapter binding order:

# PowerShell script to adjust interface metric
Get-NetAdapter | Where-Object {$_.InterfaceDescription -match "VPN"} | 
Set-NetIPInterface -InterfaceMetric 4000

# Set local Ethernet/WiFi to highest priority (lowest metric)
Get-NetAdapter | Where-Object {$_.Status -eq "Up" -and $_.InterfaceDescription -notmatch "VPN"} | 
Set-NetIPInterface -InterfaceMetric 1

Add these registry entries to enforce local DNS resolution:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"Domain"="yourdomain.local"
"SearchList"="yourdomain.local"
"UseDomainNameDevolution"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters]
"QueryOrder"=dword:00000001

Create a GPO that applies these settings:

Computer Configuration > Policies > Administrative Templates > Network > DNS Client:
- Turn off smart multi-homed name resolution: Enabled
- Primary DNS Suffix: yourdomain.local
- Append parent suffixes of the primary DNS suffix: Disabled

For small networks, manually map critical servers:

# C:\Windows\System32\drivers\etc\hosts
192.168.1.100  fileserver
192.168.1.101  printserver
192.168.1.102  appserver

Many VPN clients allow split-tunneling configuration. For OpenVPN:

# Add to client.ovpn
route-nopull
route 192.168.1.0 255.255.255.0
dhcp-option DNS 192.168.1.1

For Cisco AnyConnect, use the preference XML:

<AnyConnectPreferences>
  <DefaultUser>user</DefaultUser>
  <LocalLanAccess>true</LocalLanAccess>
  <AutoConnectOnStart>true</AutoConnectOnStart>
  <AutoUpdate>false</AutoUpdate>
</AnyConnectPreferences>