Figure 4.166Switching > Dhcp Snooping > L2 Relay > Vlan Configuration - Advantech EKI-9516P-HV User Manual

The following table describes the items in the previous figure.
Item Description
Interface The interface associated with the rest of the data in the row. When
configuring the settings for one or more interfaces, this field identifies
each interface that is being configured.
L2 Relay Mode The administrative mode of L2 relay mode on the interface. When
enabled, the interface can act as a DHCP relay agent and add informa-
tion that the L3 relay agent and DHCP server need to perform their
roles in IP address configuration and assignment.
Trust Mode The L2 relay trust mode for the interface, which is one of the following:
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
Refresh Click Refresh to update the screen.
Edit Click Edit to edit the selected entries.
VLAN Configuration
Use the DHCP L2 Relay VLAN Configuration page to control the DHCP L2 relay set-
tings on a particular VLAN. The VLAN is identified by a service VLAN ID (S-VID),
which a service provider uses to identify a customer's traffic while traversing the pro-
vider network to multiple remote sites. The device uses the VLAN membership of the
switch port client (the customer VLAN ID, or C-VID) to perform a lookup on a corre-
sponding S-VID.
To access this page, click Switching > DHCP Snooping > L2 Relay > VLAN Con-
figuration.
Figure 4.166 Switching > DHCP Snooping > L2 Relay > VLAN Configuration
The following table describes the items in the previous figure.
Item Description
VLAN ID The VLAN associated with the rest of the data in the row. When config-
uring the settings for one or more VLANs, this field identifies each
VLAN that is being configured.
Circuit ID The administrative mode of the circuit ID. When enabled, if a client
sends a DHCP request to the device and the client is in a VLAN that
corresponds to the S-VID, the device adds the client's interface num-
ber to the Circuit ID sub-option of Option 82 in the DHCP request
packet. This enables the device to reduce the broadcast domain to
which the server replies are switched when the broadcast bit is set for
DHCP packets. When this bit is set, the server is required to echo
Option 82 in replies. Since the circuit-id field contains the client inter-
face number, the L2 relay agent can forward the response to the
requesting interface only, rather to all ports in the VLAN).
Trusted: A trusted interface usually connects to other agents or
servers participating in the DHCP interaction (e.g. other L2 or L3
relay agents or servers). An interface in this mode always
expects to receive DHCP packets that include Option 82 informa-
tion. If Option 82 information is not included, these packets are
discarded.
Untrusted: An untrusted interface is generally connected to cli-
ents. DHCP packets arriving on an untrusted interface are never
expected to carry Option 82 and are discarded if they do.
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