H3C SR8800-F, Configuration Manual

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Figure 45 Trusted and untrusted ports
In a cascaded network as shown in Figure 46 , configure the DHCP snooping devices' ports facing
the DHCP server as trusted ports. To save system resources, you can enable only the untrusted
ports directly connected to the DHCP clients to record DHCP snooping entries.
Figure 46 Trusted and untrusted ports in a cascaded network
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
"
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
Table 8 . 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.
DHCP snooping
Switch A
DHCP snooping
Switch C
DHCP client
Host D
DHCP client
Host C
DHCP client
Host B
DHCP server
Device
DHCP snooping
Switch B
GE1/0/4 GE1/0/2
GE1/0/3
GE1/0/1
GE1/0/2
GE1/0/3
GE1/0/4
GE1/0/2 GE1/0/1
GE1/0/3
GE1/0/1
DHCP client
Host A
GE1/0/1
Untrusted ports enabled to record snooping entries
Untrusted ports disabled from recording snooping entries
Trusted ports