Technical Reference; Dhcp Snooping Overview - ZyXEL Communications GS1350 Series User Manual

Table 86 Advanced Application > DHCP Snooping > Configure > VLAN > Port (continued)
L ABEL
Option 82 Profile
Add
Cancel
Clear
Index
VID
Port
Profile Name
Delete
Cancel
23.4 T e c hnic a l Re fe re nc e
This section provides technical background information on the topics discussed in this chapter.
23.4.1 DHC P Sno o ping O ve rvie w
Use DHCP snooping to filter unauthorized DHCP packets on the network and to build the binding table
dynamically. This can prevent clients from getting IP addresses from unauthorized DHCP servers.
23.4.1.1 T ruste d vs. Untruste d Po rts
Every port is either a trusted port or an untrusted port for DHCP snooping. This setting is independent of
the trusted/untrusted setting for ARP inspection. You can also specify the maximum number for DHCP
packets that each port (trusted or untrusted) can receive each second.
Trusted ports are connected to DHCP servers or other switches. The Switch discards DHCP packets from
trusted ports only if the rate at which DHCP packets arrive is too high. The Switch learns dynamic
bindings from trusted ports.
Note: If DHCP is enabled and there are no trusted ports, DHCP requests will not succeed.
Untrusted ports are connected to subscribers. The Switch discards DHCP packets from untrusted ports in
the following situations:
Chapter 23 DHCP Snooping
DESC RIPT IO N
Select a pre-defined DHCP option 82 profile that the Switch applies to the specified port(s)
in this VLAN. The Switch adds the information (such as slot number, port number, VLAN ID
and/or system name) specified in the profile to DHCP requests that it broadcasts to the
DHCP VLAN, if specified, or VLAN. You can specify the DHCP VLAN in the
screen (see Section 23.3 on page
C o nfig ure
The profile you select here has priority over the one you select in the
> screen.
C o nfig ure VL A N
Click this to create a new entry or to update an existing one.
This saves your changes to the Switch's run-time memory. The Switch loses these changes if
it is turned off or loses power, so use the
changes to the non-volatile memory when you are done configuring.
Click this to reset the values above based on the last selected entry or, if not applicable, to
clear the fields above.
Click to reset the fields to the factory defaults.
C le a r
This field displays a sequential number for each entry. Click an index number to change the
settings.
This field displays the VLAN to which the ports belong.
This field displays the ports to which the Switch applies the settings.
This field displays the DHCP option 82 profile that the Switch applies to the ports.
Select the entries that you want to remove in the
button to remove the selected entries from the table.
Click this to clear the
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GS1350 Series User's Guide
193
188).
link on the top navigation panel to save your
Sa ve
De le te
check boxes above.
DHC P Sno o ping
DHC P Sno o ping
column, then click the
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>