7.3.1.1.1 Server Screening; Binding Table; Figure 24: Dhcp Snooping - WAGO 852-1305 Manual

98 Enhanced Features
The main purposes of the "DHCP Snooping" are:
1 To create and maintain a binding table for the ARP Inspection function.
2 To filter packets from DHCP servers that are connected to an "Untrusted
Port".

Figure 24: DHCP Snooping

The packets from DHCP servers connected to an "Untrusted Port" are filtered.

7.3.1.1.1 Server Screening

The switch supports "Server Screening", a function that denies access to "Rogue
DHCP Servers" (unauthorized, invalid DHCP servers). That is, when one or more
DHCP servers are present on the network and both provide DHCP services to
different distinct groups of clients, the valid DHCP server's packets are passed to
the client.
If this function is enabled, the "DHCP Snooping" function must also be enabled
beforehand. The switch allows users to configure up to three valid DHCP servers.
If no DHCP servers are configured, it means all DHCP server are valid.
7.3.1.2

Binding Table

The "DHCP Snooping" binding table records the host information learned from
"DHCP Snooping" (dynamic) or set by user (static). The ARP inspection uses this
table to decide if to forward or drop ARP packets. ARP packets sent from by
invalid hosts are dropped. Once the "Lease Time" expires, the entry is deleted
from the table.
Static bindings are uniquely identified by the MAC address and VLAN ID. Each
MAC address and VLAN ID can only be in one static binding. If you create a
static binding with the MAC address and VLAN ID of an existing binding, the
new static binding replaces the original on.
Bindings are used by "DHCP Snooping" and ARP inspection to distinguish
between authorized and unauthorized packets in the network. The switch detects
the dynamic bindings by "snooping" DHCP packets and from static information
from the manual entries in the "Static Entry Settings" menu.
WAGO-ETHERNET-Zubehör 852
852-1305 8/4-Port 100BASE-T/1000BASE-SX/LX
Manual
1.1.0