H3C Technologies H3C S12500 Series Switches - Manual (Page 73)

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Figure 23 Trusted and untrusted ports
In a cascaded network as shown in
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Figure 24 , configure each DHCP snooping device's ports connected
to other DHCP snooping devices as trusted ports. To save system resources, you can disable the untrusted
ports that are not directly connected to DHCP clients from generating DHCP snooping entries.
Figure 24 Trusted and untrusted ports in a cascaded network
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DHCP snooping support for Option 82
Option 82 records the location information about the DHCP client so the administrator can locate the
DHCP client for security and accounting purposes. For more information about Option 82, see "
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Relay
agent option (Option 82) ."
DHCP snooping uses the same strategies as the DHCP relay agent to handle Option 82 for DHCP
request messages, as shown in
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Table 4 . If a response returned by the DHCP server contains Option 82,
DHCP snooping removes Option 82 before forwarding the response to the client. If the response contains
no Option 82, DHCP snooping forwards it directly.