ProCurve 8200zl Uživatelská příručka stáhnout pdf (Strana 289)

IP Routing Features

Configuring DHCP Relay

addressing it will return to the client through the usual DHCP server response

packet. This operation provides several advantages over DHCP without

Option 82:

■ An Option 82 DHCP server can use a relay agent’s identity and client

source port information to administer IP addressing policies based on

client and relay agent location within the network, regardless of whether

the relay agent is the client’s primary relay agent or a secondary agent.

■ A routing switch operating as a primary Option 82 relay agent for DHCP

clients requesting an IP address can enhance network access protection

by blocking attempts to use an invalid Option 82 field to imitate an

authorized client, or by blocking attempts to use response packets with

missing or invalid Option 82 suboptions to imitate valid response packets

from an authorized DHCP server.

■ An Option 82 relay agent can also eliminate unnecessary broadcast traffic

by forwarding an Option 82 DHCP server response only to the port on

which the requesting client is connected, instead of broadcasting the

DHCP response to all ports on the VLAN.

Note The routing switch’s DHCP Relay Information (Option 82) feature can be used

in networks where the DHCP server(s) are compliant with RFC 3046 Option

82 operation. DHCP Servers that are not compliant with Option 82 operation

ignore Option 82 fields. For information on configuring an Option 82 DHCP

server, refer to the documentation provided with the server application.

Some client applications can append an Option 82 field to their DHCP

requests. Refer to the documentation provided for your client application.

It is not necessary for all relay agents on the path between a DHCP client and

the server to support Option 82, and a relay agent without Option 82 should

forward DHCP packets regardless of whether they include Option 82 fields.

However, Option 82 relay agents should be positioned at the DHCP policy

boundaries in a network to provide maximum support and security for the IP

addressing policies configured in the server.

Option 82 Server Support

To apply DHCP Option 82, the routing switch must operate in conjunction

with a server that supports Option 82. (DHCP servers that do not support

Option 82 typically ignore Option 82 fields.) Also, the routing switch applies

Option 82 functionality only to client request packets being routed to a DHCP

server. DHCP relay with Option 82 does not apply to switched (non-routed)

client requests.

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ProCurve 8200zl Uživatelská příručka Strana 289