R2511-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V5)

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Application of trusted and untrusted ports
Configuring a trusted port connected to a DHCP server
Figure 30 Configuring trusted and untrusted ports
Configuring trusted ports in a cascaded network
In a cascaded network as shown in Figure 31, each DHCP snooping device's ports connected to other
DHCP snooping devices should be configured as trusted ports.
To save system resources, you can disable the trusted ports that are not directly connected to DHCP
clients from recording client IP-to-MAC bindings (DHCP snooping entries) upon receiving DHCP requests.
Figure 31 Configuring trusted ports in a cascaded network
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
Eth1/4 Eth1/2
Eth1/3
Eth1/1 Eth1/2
Eth1/3
Eth1/4
Eth1/2
Eth1/1
Eth1/3
Eth1/1
DHCP client
Host A
Eth1/1
Untrusted ports
Trusted ports disabled from recording binding entries
Trusted ports enabled to record binding entries