When Remote Access Service (RAS) uses Dynamic Host Configuration Protocol(DHCP) to obtain IP addresses for dial-in clients, only the IP addressfrom the DHCP lease is passed to the RAS client. Other options in the DHCPscope are not. This article describes the behavior that occurs.
The RAS help file states, "Use DHCP to assign remote TCP/IP client addresses."
RAS servers can obtain IP addresses for remote clients from a dynamic hostconfiguration protocol (DHCP) server. DHCP servers provide static anddynamic IP address allocation on a large network. You should select thisoption if a DHCP server is available.
When the RAS server starts up with the option to Use DHCP to assign remote TCP/IP addresses
, it makes several DHCP requests in advance and caches the DHCP leases that it will need for dial-in clients. The RAS Server will request a number of addresses according to the behavior defined in the following article:
RAS Server Behavior When Configured to Use DHCP [ntrelease]
The RAS server records the address of the DHCP server, the leased IPaddress, when the lease was obtained, when the lease expires, and thelease length. All other DHCP options defined for that scope are discarded.When the client dials into the RAS server and requests an IP address("Server Assigned IP Address" is selected) the RAS server will use one ofthese cached leases. The IP address is then given to the dial-in client,which is unaware that the IP address has been obtained through DHCP. TheRAS server maintains the lease on behalf of the client. Therefore, theonly information that the client receives from the DHCP lease is the IPaddress.
When a RAS client obtains an IP address Lease from a RAS server, Winipcfg.exe (for Windows 95) or Ipconfig.exe (for Windows NT and later) displays the following information about the Lease:
Lease Obtained: Tue Jan 1 80 12:00:00 AM Lease Expires: Tue Jan 1 80 12:00:00 AM
When a RAS server assigns an IP address to a RAS client either from a Static Address Pool or DHCP, there is no real lease time for the IP address since it will be released when client disconnects.
However, RAS clients can still receive additional TCP/IP configuration information from the RAS server. WINS server assignments and Domain Name Service (DNS) server assignments can be delegated to the client when it connects.
Again, this information is not taken from the Options given in the DHCP lease. Instead, this information is taken directly from the RAS server's settings. If a RAS server has WINS or DNS entries, these entries are passed to the client.
Here is a list of the DHCP Options that Microsoft DHCP clients can support and how a RAS client obtains them:
As described above, the RAS server obtains an IP address from the DHCPserver. The RAS server then gives the IP address to the dial-in client andmanages its lease. This is the only information from the DHCP server thatthe RAS client receives.
This is taken from the RAS server if the RAS server is configured withWINS addresses. The client acquires the list of WINS servers that areconfigured on the RAS server.
This is taken from the RAS server if the RAS server is configured with DNSserver addresses. The client acquires the first DNS server addresslisted in the RAS server's DNS Service Search Order.
The subnet mask corresponds to the standard mask associated with thestandard class type of the given IP address.NOTE
: Note that Windows 2000 clients use a subnet mask of 255.255.255.255 (not the classful mask for the IP address) on PPP links.
NetBIOS Scope ID
NetBIOS scope ID information is not passed to the client. If you need tomodify this setting it will have to be changed directly on the client.
Node Type is not taken from the DHCP lease but can change on the RASclient depending on WINS information. If the RAS server has no WINSservers defined locally, a b-node Windows NT RAS client remains ab-node client. If the RAS server has WINS servers defined locally, ab-node Windows NT RAS client switches to h-node for the duration of theconnection.NOTE
: Windows 95 clients do not automatically switch between node-types if the RAS server supplies WINS addresses. This must be done manually: Click Control Panel and double-click Network
. On the Selection
tab, select TCP/IP
from the list of installed network components and then click Properties
. Click the WINS Configuration
tab, and then either manually specify the WINS addresses or click Use DHCP for WINS Resolution
An IP address obtained from a dial-up connection cannot be released or renewed with the Winipcfg.exe utility in Windows 98 or Windows 95.The Winipcfg.exe utility can only release IP addresses obtained from DHCP.
Because dial-up clients obtain IP addresses from the Remote Access Service rather than from DHCP, dial-up clients retain this address until the session disconnects.
For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
DHCP Options Supported by Clients
RAS Server Assigns Cached IP Addresses to RAS Clients
DNS Address from RAS Server Not Passed to RAS Client
Default Node Type For Microsoft Clients