How Dhcp Works - Bay Networks Baystream 7 Configuration And Troubleshooting Manual

Configuring and Troubleshooting Bay Dial VPN Services
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How DHCP Works

DHCP implements the concept of IP address leasing. An authenticated, dial-in
user receives an exclusive right to use an assigned IP address for a specific,
configurable period of time, called a "lease." When this lease expires, the DCHP
client proxy can renew the lease or let it lapse, returning the IP address to the pool.
DHCP lets a network manager designate a range of assignable IP addresses
without requiring that each IP address be tied to a specific MAC (hardware)
address. The DHCP server leases an IP address to each dial-in user and
dynamically maintains a table that links a user's IP and MAC addresses. For users
who need a fixed IP address, a network manager can also specify a permanent
assignment. A single NAS can communicate with and maintain DHCP leases with
up to as many DHCP servers as there are ports on the NAS (up to 48 or 62,
depending on the model).
When a remote user dials in to a remote access server (NAS), Dial VPN performs
the usual authentication functions. When the gateway returns the Mobile IP (MIP)
authentication response to the NAS, however, the NAS sends the gateway a MIP
dynamic address allocation (DAA) request. The gateway sends a DHCP discover
request to the DHCP server on the home network, and the server responds with an
acknowledgment (ACK) if the request is successful. The gateway then sends the
MIP DAA response back to the NAS, and the rest of the negotiation proceeds as
usual.
2-8
Getting IP addresses through either the local or the remote DHCP client
proxy, in addition to other methods that Dial VPN supports, depending on
how the Dial VPN subscriber is provisioned
Figure 2-3 shows the entire process.
BayStream Multiservice Software Version 7.2 115623B Rev. 00