Technical Reference; Dhcp Snooping Overview - ZyXEL Communications XMG1930-30 User Manual

The following table describes the labels in this screen.
Table 292 SECURITY > IPv4 Source Guard > DHCP Snooping > DHCP Snp. VLAN Port Setup > Add/Edit
LABEL
VID
Port
Option 82 Profile
Apply
Clear
Cancel

74.7 Technical Reference

This section provides technical background information on the topics discussed in this chapter.

74.7.1 DHCP Snooping Overview

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.
74.7.1.1 Trusted vs. Untrusted Ports
Every port is either a trusted port or an untrusted port for DHCP snooping. This setting is independent of
the trusted or 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:
• The packet is a DHCP server packet (for example, OFFER, ACK, or NACK).
• The rate at which DHCP packets arrive is too high.
Chapter 74 DHCP Snooping
DESCRIPTION
Enter the ID number of the VLAN you want to configure here.
Enter the number of ports to which you want to apply the specified DHCP option 82 profile.
You can enter multiple ports separated by (no space) comma (,) or hyphen (-) for a range.
For example, enter "3-5" for ports 3, 4, and 5. Enter "3,5,7" for ports 3, 5, and 7.
Select a pre-defined DHCP option 82 profile that the Switch applies to the specified ports 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 SECURITY > IPv4 Source
Guard > DHCP Snooping > DHCP Snp. Setup screen.
Note: The profile you select here has priority over the one you select in the
SECURITY > IPv4 Source Guard > DHCP Snooping > DHCP Snp. VLAN Setup
screen.
Click Apply to save 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 Save link on the top navigation panel to
save your changes to the non-volatile memory when you are done configuring.
Click Clear to clear the fields to the factory defaults.
Click Cancel to not save the configuration you make and return to the last screen.
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