When ISG is in the path of DHCP requests, ISG can influence the IP address pool and DHCP servers that are used to assign subscriber IP addresses. This is achieved by configuring a DHCP address pool. As a result on a per-request basis, an IP address is either provided by local DHCP server or relayed to a remote DHCP server that is defined in selected pool.

The DHCP RADIUS Proxy with ISG feature enables downloading of the DHCP parameters like IPv4 address, mask, lease time, and so on from RADIUS as part of the Access-Accept message. DHCP RADIUS Proxy with ISG feature supports allocation of client IP addresses using parameters that are downloaded using RADIUS or using locally configured pool.

Note	If static IP is provided by RADIUS, then it must be used to configure the client. If Static IP is not provided, IP is allocated dynamically using the locally configured pool or using Relay.

In the above figure:

• End user sends DHCP-Discover message to ISG.

• To initiate session based on DHCP, ISG asks RADIUS with Access-Request

• RADIUS answers with Access-Accept and sends static IP address (RADIUS Attribute 8 Framed-IP-Address) and other parameters like lease time, gateway, and so on.

• ISG receives this Accept message, parses the address, adds DHCP binding for this subscriber, and sends DHCP Offer with proposed IP address and other DHCP parameters (Lease Time and Gateway).

• ISG starts the new subscriber session.

The following RADIUS parameters can be downloaded to trigger DHCP Radius Proxy feature:

Cleartext-Password := "cisco"
               Service-Type = Framed-User,
               Framed-IP-Address = 10.0.0.3,
               Framed-IP-Netmask = 255.255.0.0,
               Framed-Route += "192.0.2.1 255.255.255.0 203.0.113.1",
               Cisco-AVPair += "ip:lease-duration=600",
               Cisco-AVPair += "ip:default-ipv4-gateway=10.0.0.1",
               Cisco-AVPair += "ip:primary-dns=10.40.0.1",
               Cisco-AVPair += "ip:secondary-dns=10.0.0.2",
               Cisco-AVPair += "ip:vrf-id=RED",
               Cisco-AVPair += "subscriber:classname=dhcp-red-class",

Use the following command to find if the DHCP IP Address is assigned dynamically or through RADIUS Proxy.

Note	The Type field for RADIUS Proxy is ISG if IP address is obtained from RADIUS. If IP address is assigned from local pool, the Type field is Automatic.

Device# show ip dhcp binding
Bindings from VRF pool RED:
IP address      Client-ID/                     Lease expiration            Type       State      Interface Hardware address/ User name

10.0.0.3        0100.0000.0000.03       	May 21 2017 02:56 AM         ISG        Active     multiservice0