IP Routing Features

Configuring DHCP Relay

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 validation of server responses for three of the policy types (append, replace, or drop).

Table 7-3.

Configuration Options for Managing DHCP Client Request Packets

 

 

 

 

Option 82

 

DHCP Client Request Packet Inbound to the Routing Switch

Configuration

 

 

Packet Has No

Packet Includes an Option 82 Field

 

 

 

 

Option 82 Field

 

Append

 

Append an

Append allows the most detail in defining DHCP policy boundaries. For example,

 

 

Option 82 Field

where the path from a client to the DHCP Option 82 server includes multiple relay

 

 

 

agents with Option 82 capability, each relay agent can define a DHCP policy

 

 

 

boundary and append its own Option 82 field to the client request packet. The server

 

 

 

can then determine in detail the agent hops the packet took, and can be configured

 

 

 

with a policy appropriate for any policy boundary on the path.

 

 

 

Note: In networks with multiple relay agents between a client and an Option 82

 

 

 

server, append can be used only if the server supports multiple Option 82 fields in

 

 

 

a client request. If the server supports only one Option 82 field in a request, consider

 

 

 

using the keep option.

 

 

 

 

Keep

 

Append an

If the relay agent receives a client request that already has one or more Option 82

 

 

Option 82 Field

fields, keep causes the relay agent to retain such fields and forward the request

 

 

 

without adding another Option 82 field. But if the incoming client request does not

 

 

 

already have any Option 82 fields, the relay agent appends an Option 82 field before

 

 

 

forwarding the request. Some applications for keep include:

 

 

 

• The DHCP server does not support multiple Option 82 packets in a client request

 

 

 

and there are multiple Option 82 relay agents in the path to the server.

 

 

 

• The unusual case where DHCP clients in the network add their own Option 82

 

 

 

fields to their request packets and you do not want any additional fields added

 

 

 

by relay agents.

 

 

 

This policy does not include the validate option (described in the next section) and

 

 

 

allows forwarding of all server response packets arriving inbound on the routing

 

 

 

switch (except those without a primary relay agent identifier.)

 

 

 

 

7-34