User Guide
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When DHCP relay is enabled and Client sends out DHCP REQUEST packets, follow below steps to
configure the switch:
1. View corresponding server ID of VLAN virtual interface 2 from the DHCP Relay Setup interface, say
2.
2. View corresponding IP of this server ID, say 2.2.2.20.
3. View the corresponding VLAN virtual interface which is in the same network segment as the IP in step
2, say VLAN virtual interface 3.
4. View corresponding VLAN ID of the VLAN virtual interface, say VLAN 3.
5. Packets will be forwarded to ports in VLAN 3 as step 4 describes.
Note-------------------------------------------------------------------------------------------------------------------------------
As for servers in VLAN 3, you need to set its DHCP server’s DHCP relay IP to 1.1.1.1 so that clients in
VLAN 2 can obtain IP automatically from the DHCP server in VLAN 3.
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4.6.7 DHCP Snooping
DHCP Snooping Functions
In computer networking, DHCP snooping is a series of techniques applied to ensure the security of an
existing DHCP infrastructure. Its functions are as below:
Ensure that clients only obtain IP addresses legal servers assign to them.
If illegal DHCP servers exist in computer networking, DHCP clients might obtain incorrect IP addresses
and parameters, thus leading to abnormal communication. In order that DHCP clients obtain IP
addresses via legal DHCP servers, trusted ports and untrusted ports are allowed:
Trusted ports can forward DHCP packets they’ve received.
After receiving DHCP-ACK and DHCP-OFFER packets, untrusted ports will discard these packets.
Ports which are connected to DHCP servers and other DHCP Snooping devices need to be configured as
trusted ports and other ports need to be configured as untrusted ports, so that DHCP clients can only
obtain IP addresses from legal DHCP clients.
Record the corresponding relation between DHCP client’s IP address and MAC address.
By snooping DHCP-REQUEST and DHCP-ACK broadcast packets trust ports have received, it records
DHCP Snooping entries, including clients’ MAC addresses, obtained IP addresses, ports connected to
DHCP clients, ports’ belonging VLAN info, etc.
Global Setup
To configure DHCP snooping global settings, click Device Management -> DHCP Snooping -> Global
Setup as below:
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