Zyxel XGS3700-24HP [295/548] Dhcp snooping overview

Zyxel XGS3700-24HP [295/548] Dhcp snooping overview
Chapter 25 IP Source Guard
GS3700/XGS3700 Series User’s Guide
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The following table describes the labels in this screen.
25.17 Technical Reference
This section provides technical background information on the topics discussed in this chapter.
25.17.1 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.
25.17.1.1 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/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: The Switch will drop all DHCP requests if you enable DHCP snooping and there are
no trusted ports.
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).
Table 141 Advanced Application > IP Source Guard > IPv6 DHCP Trust Setup (Standalone mode)
LABEL DESCRIPTION
Active Select this to specify whether ports are trusted or untrusted ports for DHCP snooping. If
you do not select this then IPv6 DHCP Trust is not used and all ports are automatically
trusted.
Port This field displays the port number. If you configure the * port, the settings are applied to
all of the ports.
Trusted state Select whether this port is a trusted port (Trusted) or an untrusted port (Untrusted).
Trusted ports are connected to DHCPv6 servers or other switches.
Untrusted ports are connected to subscribers, and the Switch discards DHCPv6 packets
from untrusted ports in the following situations:
The packet is a DHCPv6 server packet (for example, ADVERTISE, REPLY, or RELAY-
REPLY).
The source MAC address and source IP address in the packet do not match any of the
current bindings.
Apply Click Apply to save your changes to the Switchs 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.
Cancel Click this to reset the values in this screen to their last-saved values.

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