The “ip dhcp trust” command is typically used on a layer two interface of a network device, such as a switch, to indicate that the device should trust DHCP messages received on that interface because DHCP is a protocol that malicious actors can exploit to gain unauthorized access to a network, and the “ip dhcp trust” command helps to mitigate this risk by preventing unauthorized DHCP servers from distributing IP addresses to devices on the network.

On the other hand, a layer three interface is used to route traffic between networks and does not typically have anything to do with the DHCP protocol. Since a layer three interface is not involved in the delivery or processing of DHCP messages, there is no need to implement the “ip dhcp trust” command on a layer three interface. That being said, it is essential to implement appropriate security measures on all network devices and interfaces to ensure the integrity and confidentiality of the network, which might include efforts such as access controls, network segmentation, and network monitoring to detect and respond to security threats.

Why is the “no option 82” used when configuring ip dhcp snooping?

The “no option 82” command configures DHCP snooping on a network device, typically a switch. DHCP snooping is a security feature that prevents rogue DHCP servers from providing invalid IP addresses or other network configuration information to devices on a network.

When a DHCP client sends a request to obtain an IP address, it includes specific information in the request packet, including the client’s MAC address, the requested IP address, and other configuration parameters. One of these parameters is the DHCP Option 82, a field used to identify the physical port on the switch where the client is connected. The DHCP server uses this information to assign an IP address to the client and the network device to verify that the DHCP response is from a valid DHCP server. However, using DHCP Option 82 can cause problems in some cases, particularly in complex network topologies or environments where multiple DHCP servers are used. For example, in some cases, using Option 82 can cause IP addresses to be assigned incorrectly or can cause DHCP requests to be dropped by the network device. The “no option 82” command is used to disable DHCP Option 82 on a network device, which can help prevent these types of issues and ensure that DHCP requests and responses are handled correctly by the network device and any DHCP servers on the network.

Why is an “ip helper address” needed on a routed interface?

The “ip helper-address” command is typically used on a routed interface of a network device, such as a router or layer three switches, to enable forwarding certain types of traffic between different network segments. In particular, the “ip helper-address” command is used to forward broadcast traffic, such as DHCP requests or other types of network discovery protocols, from one network segment to another. When a client device on one network segment sends a broadcast request for a particular service, such as DHCP, the broadcast packet is not forwarded by default to other network segments since broadcasts are typically limited to the local network segment. However, by configuring the “ip helper-address” command on a routed interface, the router can be configured to forward these broadcast packets to a specific destination address, such as the IP address of a DHCP server on a different network segment.

For example, suppose that two network segments, A and B, are separated by a router. If a client on network segment A sends a DHCP request, the broadcast packet will not be forwarded to network segment B by default. However, suppose the router interface that connects to network segment A is configured with the “ip helper-address” command and the IP address of the DHCP server on network segment B. In that case, the router will forward the DHCP request to the DHCP server on network segment B. The DHCP server can then respond to the client via the router, allowing the client to obtain an IP address from the DHCP server on the other network segment.

In summary, the “ip helper-address” command is used on a routed interface to enable the forwarding of certain types of broadcast traffic between different network segments, such as DHCP requests or other types of network discovery protocols.