dial-up network adapter, how is subnet determined?

deleyd
deleyd used Ask the Experts™
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Windows 7 Network Adapter to modem; Network Adapter IP address setting has no subnet mask. It looks like this:
TCP/IPv4 Properties "Use the following IP address:"The instructions then say, "The IP address you manually assigned to the new dial-up network adapter (172.10.10.1) functions as a gateway to any valid IP address on that subnet."

There is no place for me to specify what the subnet is.

ipconfig/all shows:
PPP adapter Dial-up Connection

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Dial-up Connection
   Physical Address. . . . . . . . . :
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   IPv4 Address. . . . . . . . . . . : 172.10.10.1(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . :
   NetBIOS over Tcpip. . . . . . . . : Disabled

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Here it says "Preferred" for IPv4 address. What does "Preferred" mean?
Subnet Mask is 255.255.255.255 What does that mean?

What is the subnet, and how does this act as a gateway to that subnet?
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Dr. KlahnPrincipal Software Engineer

Commented:
Are you dialing in to an ISP?  Normally what happens in that case is that the PPP connection is established, the credentials are verified, then the client obtains an IP address on the subnet from a DHCP server over the PPP link.  In that situation subnetting is not the responsibility of the client; TCP configuration is done using information obtained via DHCP.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
"Preferred" for IPv4 address. What does "Preferred" mean?   <-- Dial up does not use IPv6 so far as I know, so IPv4 is "preferred"

Subnet Mask is 255.255.255.255 What does that mean?  <-- It got one address (172.10.10.1) and not a subnet.

As per above, what exactly are you dialing into?

Commented:
Dialling in is was never designed to work like a LAN. So not sure why you want to be able to. If you want to share with others, use other (host-based) tools.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
I think (long time back) you can dial into a VPN box and use VPN to get a subnet at the other end. Too long ago now to remember accurately.
Software Engineer
Commented:
Some research and I determined this is a "classful IP Address" starting with 172 so it's a "Class B" and the subnet mask for that class is 255.255.0.0

Testing showed it behaves that way.

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