IP Configuration
IPv4 Management and Interfaces
Cisco 350XG & 550XG Series 10G Stackable Managed Switches
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Overview
DHCPv4 Snooping Overview
DHCP snooping provides a security mechanism to prevent receiving false DHCP
response packets and to log DHCP addresses. It does this by treating ports on the
device as either trusted or untrusted.
A trusted port is a port that is connected to a DHCP server and is allowed to
assign DHCP addresses. DHCP messages received on trusted ports are allowed
to pass through the device.
An untrusted port is a port that is not allowed to assign DHCP addresses. By
default, all ports are considered untrusted until you declare them trusted (in the
DHCPv4 Relay Overview
DHCP Relay relays DHCP packets to the DHCP server.
The device can relay DHCP messages received from VLANs that do not have IP
addresses. Whenever DHCP Relay is enabled on a VLAN without an IP address,
Option 82 is inserted automatically. This insertion is in the specific VLAN and does
not influence the global administration state of Option 82 insertion.
Transparent DHCP Relay
For Transparent DHCP Relay where an external DHCP relay agent is being used,
do the following:
•
Enable DHCP Snooping.
•
Enable Option 82 insertion.
•
Disable DHCP Relay.
For regular DHCP Relay:
•
Enable DHCP Relay.
•
No need to enable Option 82 insertion.
Option 82
Option 82 (DHCP Relay Agent Information Option) passes port and agent
information to a central DHCP server, indicating where an assigned IP address
physically connects to the network.
