Dynamic ARP Inspection (DAI) can be enabled globally for a specific VLAN with the command `ip arp inspection vlan <vlan-id>`. By default, all ports are set to untrusted. To configure a port as trusted, use the command `ip arp inspection trust` at the interface level.
To enable Dynamic ARP Inspection (DAI) on a specific VLAN and configure a switch port as trusted, follow these detailed steps:
### Enabling DAI on a Specific VLAN
1. **Access Global Configuration Mode**:
Start by entering global configuration mode on the switch.
```plaintext
OmniSecuSW1# configure terminal
```
2. **Enable DAI for the Desired VLAN**:
Use the following command to enable Dynamic ARP Inspection for VLAN 500. Replace `500` with your desired VLAN ID.
```plaintext
OmniSecuSW1(config)# ip arp inspection vlan 500
```
3. **Exit Configuration Mode**:
After configuring the VLAN for DAI, exit back to the privileged EXEC mode.
```plaintext
OmniSecuSW1(config)# exit
OmniSecuSW1#
```
### Configuring a Switch Port as Trusted
1. **Re-enter Global Configuration Mode**:
If you have exited to privileged EXEC mode, enter global configuration mode again.
```plaintext
OmniSecuSW1# configure terminal
```
2. **Select the Interface to Trust**:
Specify the interface you want to configure as trusted. In this example, we are using `GigabitEthernet 0/0`.
```plaintext
OmniSecuSW1(config)# interface gigabitethernet 0/0
```
3. **Configure the Interface as Trusted**:
Use the following command to mark the selected interface as trusted for ARP packets.
```plaintext
OmniSecuSW1(config-if)# ip arp inspection trust
```
4. **Exit Interface Configuration Mode**:
Once the trusted configuration is applied, exit interface configuration mode.
```plaintext
OmniSecuSW1(config-if)# exit
```
5. **Exit Global Configuration Mode**:
Finally, exit the global configuration mode to return to the privileged EXEC mode.
```plaintext
OmniSecuSW1(config)# exit
OmniSecuSW1#
```
### Additional Considerations
- **Trusted vs. Untrusted Ports**: By default, all switch ports are untrusted, meaning DAI will inspect ARP packets and discard any that do not match valid bindings. Trusted ports, typically connected to legitimate devices (like DHCP servers), are exempt from inspection.
- **Verify Configuration**: After configuring DAI, it’s a good practice to verify your settings using the following command:
```plaintext
OmniSecuSW1# show ip arp inspection
```
- **Check VLAN Status**: You can also check the status of DAI on a specific VLAN:
```plaintext
OmniSecuSW1# show ip arp inspection vlan 500
```
By following these steps, you can effectively enable Dynamic ARP Inspection on a specific VLAN and configure trusted ports to help prevent ARP spoofing attacks in your network.
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