PC can access shared folders on other PCs on LAN, other PCs cannot access its shared folders

I have 3 Windows 10 computers on a LAN (A, B, C), connected with a DSL modem. I am trying to access shared folders from each computer. All computers (including A) can see B & C, but B & C cannot see A (A can see itself, with \\A). All computers are running Windows 10 version 1803. A and C are running OS build 17134.165 Pro, B is running 17134.228 Home. This problem only started happening with the latest major Windows update.

"Windows cannot access \\A" Error code: 0x80004005 Unspecified error.

Troubleshooting results in

"Windows can't communicate with the device or resource. It is available but not responding to connection attempts. A firewall or network security policy on the remote computer might be blocking the connection on port "file and print sharing resource"

.

"File and Printer Sharing" is checked for both private and public in Windows Defender Firewall -> Allowed apps. I also enabled group policy Computer Configuration -> Administrative Templates -> Network -> Network Connections -> Windows Firewall -> Domain Profile -> Windows Firewall: Allow inbound file and printer sharing exception (as per https://computerstepbystep.com/windows-firewall-allow-inbound-file-and-printer-sharing-exception.html) but it made no difference. I also tried turning off windows firewall, and it made no difference.

The computers "dial" a dsl connection (using rasdial) to get their own public IP address (but not dialing this connection doesn't solve the problem). The DSL connection is a "public" network, and the "Ethernet" connection is a private network.

Both the dsl and ethernet network adapters have "File and Printer Sharing for Microsoft Networks" and "Client for Microsoft Networks" installed and enabled.

Both Private and Guest or Public network profiles have "network discovery" & "file and printer sharing" turned on.

Pinging A from B & C works and shows the right (local) ip address. Trying to open that local ip address in windows explorer (\\192.168.2.11) behaves the same as trying to open \\A.

Subnet mask is the same for all computers.

The services "Function Discovery Resource Publication" and "UPnP Device Host" were not running on A, but starting them made no difference.

I tried to enable insecure guest logons (as per https://superuser.com/a/1326327/318722 and https://support.microsoft.com/en-us/help/4046019), but that did not change anything.

I also tried to enable SMB Direct (and even SMB 1.0/CIFS Client (server was already enabled)) on A, to no avail.

Here is the output of netsh interface ip show address (as per https://superuser.com/a/1230396/318722)

For A:

Configuration for interface "Bell"

DHCP enabled:                         No
IP Address:                           74.12.xxx.xxx
Subnet Prefix:                        74.12.xxx.xxx/32 (mask 255.255.255.255)
Default Gateway:                      0.0.0.0
Gateway Metric:                       1
InterfaceMetric:                      25

Configuration for interface "Wi-Fi"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Local Area Connection* 11"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Local Area Connection* 3"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Ethernet 2"

DHCP enabled:                         Yes
InterfaceMetric:                      4260

Configuration for interface "Bluetooth Network Connection"

DHCP enabled:                         Yes
InterfaceMetric:                      4290

Configuration for interface "Loopback Pseudo-Interface 1"

DHCP enabled:                         No
IP Address:                           127.0.0.1
Subnet Prefix:                        127.0.0.0/8 (mask 255.0.0.0)
InterfaceMetric:                      4300

Configuration for interface "Ethernet"

DHCP enabled:                         Yes
IP Address:                           192.168.2.11
Subnet Prefix:                        192.168.2.0/24 (mask 255.255.255.0)
Default Gateway:                      192.168.2.1
Gateway Metric:                       0
InterfaceMetric:                      4250

and for B:

Configuration for interface "Bell"

DHCP enabled:                         No
IP Address:                           74.12.xxx.xxx
Subnet Prefix:                        74.12.xxx.xxx/32 (mask 255.255.255.255)
Default Gateway:                      0.0.0.0
Gateway Metric:                       1
InterfaceMetric:                      25

Configuration for interface "Wi-Fi"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Local Area Connection* 5"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Local Area Connection* 6"

DHCP enabled:                         Yes
InterfaceMetric:                      4250

Configuration for interface "Bluetooth Network Connection"

DHCP enabled:                         Yes
InterfaceMetric:                      4290

Configuration for interface "Loopback Pseudo-Interface 1"

DHCP enabled:                         No
IP Address:                           127.0.0.1
Subnet Prefix:                        127.0.0.0/8 (mask 255.0.0.0)
InterfaceMetric:                      4300

Configuration for interface "Ethernet"

DHCP enabled:                         Yes
IP Address:                           192.168.2.12
Subnet Prefix:                        192.168.2.0/24 (mask 255.255.255.0)
Default Gateway:                      192.168.2.1
Gateway Metric:                       0
InterfaceMetric:                      4250

I confirmed that SMB2 is running on both A & B with

Get-SmbServerConfiguration | Select EnableSMB2Protocol

as per https://www.windowscentral.com/how-access-files-network-devices-using-smbv1-windows-10, and it is.

If this showed up after a major update there could be permissions issues on the share that are getting in the way. Make sure both the share permissions and local NTFS permissions are set up to permit those other PCs to access it. The big Windows updates have a bad habit of resetting random settings to default.

You can also try temporarily disabling the firewall entirely to make sure it's not the issue, but it sounds like you've done a good job checking the network side.