Product guide

IP Routing Features
Configuring DHCP Relay
■ Circuit ID: This nonconfigurable subfield identifies the port number of
the physical port through which the routing switch received a given DHCP
client request, and is necessary to identify if you want to configure an
Option 82 DHCP server to use the Circuit ID to select a DHCP policy to
assign to clients connected to the port. This number is the identity of the
inbound port. On ProCurve fixed-port switches, the port number used for
the Circuit ID is always the same as the physical port number shown on
the front of the switch. On ProCurve chassis switches, where a dedicated,
sequential block of internal port numbers are reserved for each slot,
regardless of whether a slot is occupied, the circuit ID for a given port is
the sequential index number for that port position in the slot. (To view
the Index number assignments for ports in the routing switch, use the
walkmib ifname command.)
ProCurve# walkmib ifname
ifName.1 = 1
ifName.2 = 2
ifName.3 = 3
ifName.4 = 4
Figure 3-7. Using Walkmib To Determine the Circuit ID for a Port on a ProCurve
Chassis
For example, suppose you wanted port 10 on a given relay agent to support
no more than five DHCP clients simultaneously, you could configure the
server to allow only five IP addressing assignments at any one time for the
circuit ID (port) and remote ID (MAC address) corresponding to port 10 on
the selected relay agent.
Similarly, if you wanted to define specific ranges of addresses for clients on
different ports in the same VLAN, you could configure the server with the
range of IP addresses allowed for each circuit ID (port) associated with the
remote ID (IP address) for the selected VLAN.
Forwarding Policies
DHCP Option 82 on ProCurve switches offers four forwarding policies, with
an optional va l idation of server re sponses for three of th e policy types (append,
replace, or drop).
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