Cisco DCNM Security Configuration Guide, Release 4.1
Configuring Dynamic ARP Inspection
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Configuring Dynamic ARP Inspection

Table Of Contents

Configuring Dynamic ARP Inspection

Information About DAI

Understanding ARP

Understanding ARP Spoofing Attacks

Understanding DAI and ARP Spoofing Attacks

Interface Trust States and Network Security

Prioritizing ARP ACLs and DHCP Snooping Entries

Logging DAI Packets

Virtualization Support

Licensing Requirements for DAI

Prerequisites for DAI

Guidelines and Limitations

Configuring DAI

Enabling or Disabling DAI on VLANs

Configuring the DAI Trust State of a Layer 2 Interface

Applying ARP ACLs to VLANs for DAI Filtering

Enabling or Disabling Additional Validation

Configuring the DAI Logging Buffer Size

Configuring the DAI System Logging Rate

Configuring DAI Log Filtering

Displaying and Clearing DAI Statistics

Field Descriptions for DAI

Device: Details: Global Settings Section

Device: Details: ARP Trust State Section

VLAN: DAI VLAN Details Tab

Related Fields

Configuring ARP ACLs

Creating an ARP ACL

Changing an ARP ACL

Removing an ARP ACL

Field Descriptions for ARP ACLs

ARP ACL: ACL Details Tab

ARP Access Rule: ACE Details Tab

ARP Access Rule: ACE Details: Source and Destination Section

ARP ACL Remark: Remark Details Tab

Related Fields

Additional References

Related Documents

Standards

Feature History for DAI


Configuring Dynamic ARP Inspection


This chapter describes how to configure dynamic Address Resolution Protocol (ARP) inspection (DAI) on an NX-OS device.

This chapter includes the following sections:

Information About DAI

Licensing Requirements for DAI

Prerequisites for DAI

Guidelines and Limitations

Configuring DAI

Displaying and Clearing DAI Statistics

Field Descriptions for DAI

Configuring ARP ACLs

Field Descriptions for ARP ACLs

Additional References

Feature History for DAI

Information About DAI

This section includes the following topics:

Understanding ARP

Understanding ARP Spoofing Attacks

Understanding DAI and ARP Spoofing Attacks

Interface Trust States and Network Security

Prioritizing ARP ACLs and DHCP Snooping Entries

Logging DAI Packets

Virtualization Support

Understanding ARP

ARP provides IP communication within a Layer 2 broadcast domain by mapping an IP address to a MAC address. For example, host B wants to send information to host A but does not have the MAC address of host A in its ARP cache. In ARP terms, host B is the sender and host A is the target.

To get the MAC address of host A, host B generates a broadcast message for all hosts within the broadcast domain to obtain the MAC address associated with the IP address of host A. All hosts within the broadcast domain receive the ARP request, and host A responds with its MAC address.

Understanding ARP Spoofing Attacks

ARP spoofing attacks and ARP cache poisoning can occur because ARP allows a reply from a host even if an ARP request was not received. After the attack, all traffic from the device under attack flows through the attacker's computer and then to the router, switch, or host.

An ARP spoofing attack can affect hosts, switches, and routers connected to your Layer 2 network by sending false information to the ARP caches of the devices connected to the subnet. Sending false information to an ARP cache is known as ARP cache poisoning. Spoof attacks can also intercept traffic intended for other hosts on the subnet. Figure 12-1 shows an example of ARP cache poisoning.

Figure 12-1 ARP Cache Poisoning

Hosts A, B, and C are connected to the device on interfaces A, B, and C, all of which are on the same subnet. Their IP and MAC addresses are shown in parentheses; for example, host A uses IP address IA and MAC address MA. When host A needs to send IP data to host B, it broadcasts an ARP request for the MAC address associated with IP address IB. When the device and host B receive the ARP request, they populate their ARP caches with an ARP binding for a host with the IP address IA and a MAC address MA; for example, IP address IA is bound to MAC address MA. When host B responds, the device and host A populate their ARP caches with a binding for a host with the IP address IB and the MAC address MB.

Host C can poison the ARP caches of the device, host A, and host B by broadcasting two forged ARP responses with bindings: one for a host with an IP address of IA and a MAC address of MC and another for a host with the IP address of IB and a MAC address of MC. Host B and the device then use the MAC address MC as the destination MAC address for traffic intended for IA, which means that host C intercepts that traffic. Likewise, host A and the device use the MAC address MC as the destination MAC address for traffic intended for IB.

Because host C knows the true MAC addresses associated with IA and IB, it can forward the intercepted traffic to those hosts by using the correct MAC address as the destination. This topology, in which host C has inserted itself into the traffic stream from host A to host B, is an example of a man-in-the middle attack.

Understanding DAI and ARP Spoofing Attacks

DAI ensures that only valid ARP requests and responses are relayed. When DAI is enabled and properly configured, an NX-OS device performs these activities:

Intercepts all ARP requests and responses on untrusted ports

Verifies that each of these intercepted packets has a valid IP-to-MAC address binding before updating the local ARP cache or before forwarding the packet to the appropriate destination

Drops invalid ARP packets

DAI can determine the validity of an ARP packet based on valid IP-to-MAC address bindings stored in a Dynamic Host Configuration Protocol (DHCP) snooping binding database. This database is built by DHCP snooping if DHCP snooping is enabled on the VLANs and on the device. It can also contain static entries that you create. If the ARP packet is received on a trusted interface, the device forwards the packet without any checks. On untrusted interfaces, the device forwards the packet only if it is valid.

DAI can validate ARP packets against user-configured ARP access control lists (ACLs) for hosts with statically configured IP addresses (see the "Applying ARP ACLs to VLANs for DAI Filtering" section). The device logs dropped packets (see the "Logging DAI Packets" section).

You can configure DAI to drop ARP packets when the IP addresses in the packets are invalid or when the MAC addresses in the body of the ARP packets do not match the addresses specified in the Ethernet header (see the "Enabling or Disabling Additional Validation" section).

Interface Trust States and Network Security

DAI associates a trust state with each interface on the device. Packets that arrive on trusted interfaces bypass all DAI validation checks, and packets that arrive on untrusted interfaces go through the DAI validation process.

In a typical network configuration, the guidelines for configuring the trust state of interfaces as follows:

Untrusted—Interfaces that are connected to hosts

Trusted—Interfaces that are connected to devices

With this configuration, all ARP packets that enter the network from a device bypass the security check. No other validation is needed at any other place in the VLAN or in the network. For information about configuring the trust state of an interface, see the "Configuring the DAI Trust State of a Layer 2 Interface" section.


Caution Use the trust state configuration carefully. Configuring interfaces as untrusted when they should be trusted can result in a loss of connectivity.

In Figure 12-2, assume that both device A and device B are running DAI on the VLAN that includes host 1 and host 2. If host 1 and host 2 acquire their IP addresses from the DHCP server connected to device A, only device A binds the IP-to-MAC address of host 1. If the interface between device A and device B is untrusted, the ARP packets from host 1 are dropped by device B and connectivity between host 1 and host 2 is lost.

Figure 12-2 ARP Packet Validation on a VLAN Enabled for DAI

If you configure interfaces as trusted when they should be untrusted, you may open a security hole in a network. If device A is not running DAI, host 1 can easily poison the ARP cache of device B (and host 2, if you configured the link between the devices as trusted). This condition can occur even though device B is running DAI.

DAI ensures that hosts (on untrusted interfaces) connected to a device that runs DAI do not poison the ARP caches of other hosts in the network; however, DAI does not prevent hosts in other portions of the network from poisoning the caches of the hosts that are connected to a device that runs DAI.

If some devices in a VLAN run DAI and other devices do not, then the guidelines for configuring the trust state of interfaces on a device running DAI becomes the following:

Untrusted—Interfaces that are connected to hosts or to devices that are not running DAI

Trusted—Interfaces that are connected to devices that are running DAI

To validate the bindings of packets from devices that are not running DAI, configure ARP ACLs on the device running DAI. When you cannot determine the bindings, isolate at Layer 3 the devices that run DAI from devices that do not run DAI.


Note Depending on your network setup, you may not be able to validate a given ARP packet on all devices in the VLAN.


Prioritizing ARP ACLs and DHCP Snooping Entries

By default, DAI filters DAI traffic by comparing DAI packets to IP-MAC address bindings in the DHCP snooping database.

When you apply an ARP ACL to traffic, the ARP ACLs take precedence over the default filtering behavior.The device first compares ARP packets to user-configured ARP ACLs. If the ARP ACL denies the ARP packet, the device denies the packet regardless of whether a valid IP-MAC binding exists in the DHCP snooping database.


Note VLAN ACLs (VACLs) take precedence over both ARP ACLs and DHCP snooping entries. For example, if you apply a VACL and an ARP ACL to a VLAN and you configured the VACL to act on ARP traffic, the device permits or denies ARP traffic as determined by the VACL, not the ARP ACL or DHCP snooping entries.


For information about configuring ARP ACLs, see the "Configuring ARP ACLs" section. For information about applying an ARP ACL, see the "Applying ARP ACLs to VLANs for DAI Filtering" section.

Logging DAI Packets

NX-OS maintains a buffer of log entries about DAI packets processed. Each log entry contains flow information, such as the receiving VLAN, the port number, the source and destination IP addresses, and the source and destination MAC addresses.

You can also specify the type of packets that are logged. By default, an NX-OS device logs only packets that DAI drops. For configuration information, see the "Configuring DAI Log Filtering" section.

If the log buffer overflows, the device overwrites the oldest DAI log entries with newer entries. You can configure the maximum number of entries in the buffer. For more information, see the "Configuring the DAI Logging Buffer Size" section.


Note NX-OS does not generate system messages about DAI packets that are logged.


Virtualization Support

The following information applies to DAI used in Virtual Device Contexts (VDCs):

IP-MAC address bindings are unique per VDC.

ARP ACLs are unique per VDC. You cannot use an ACL that you created in one VDC in a different VDC.

Because ACLs are not shared by VDCs, you can reuse ACL names in different VDCs.

The system does not limit ARP ACLs or rules on a per-VDC basis.

Licensing Requirements for DAI

The following table shows the licensing requirements for this feature:

Product
License Requirement

DCNM

DAI requires a LAN Enterprise license. For a complete explanation of the DCNM licensing scheme and how to obtain and apply licenses, see the Cisco DCNM Fundamentals Configuration Guide, Release 4.1.

NX-OS

DAI requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the NX-OS licensing scheme, see the Cisco Nexus 7000 Series NX-OS Licensing Guide, Release 4.1.


Prerequisites for DAI

You should be familiar with the following before you configure DAI:

ARP

DHCP snooping

Guidelines and Limitations

DAI has the following configuration guidelines and limitations:

DAI is an ingress security feature; it does not perform any egress checking.

DAI is not effective for hosts connected to devices that do not support DAI or that do not have this feature enabled. Because man-in-the-middle attacks are limited to a single Layer 2 broadcast domain, you should separate the domain with DAI from domains without DAI. This separation secures the ARP caches of hosts in the domain with DAI.

DAI depends on the entries in the DHCP snooping binding database to verify IP-to-MAC address bindings in incoming ARP requests and ARP responses. If you want DAI to use static IP-MAC address bindings to determine if ARP packets are valid, DHCP snooping needs only to be enabled. If you want DAI to use dynamic IP-MAC address bindings to determine if ARP packets are valid, DHCP snooping must configured on the same VLANs on which you configure DAI. For configuration information, see the "Configuring DHCP Snooping" section on page 11-7.

When you use the feature dhcp command to enable the DHCP snooping feature, there is a delay of approximately 30 seconds before the I/O modules receive DHCP snooping or DAI configuration. This delay occurs regardless of the method that you use to change from a configuration with DHCP snooping disabled to a configuration with DHCP snooping enabled. For example, if you use the Rollback feature to revert to a configuration that enables DHCP snooping, the I/O modules receive DHCP snooping and DAI configuration approximately 30 seconds after you complete the rollback.

When DHCP snooping is disabled or used in a non-DHCP environment, you should use ARP ACLs to permit or to deny packets.

DAI is supported on access ports, trunk ports, port-channel ports, and private VLAN ports.

The DAI trust configuration of a port channel determines the trust state of all physical ports that you assign to the port channel. For example, if you have configured a physical port as a trusted interface and then you add that physical port to a port channel that is an untrusted interface, the physical port becomes untrusted.

When you remove a physical port from a port channel, the physical port does not retain the DAI trust state configuration of the port channel.

When you change the trust state on the port channel, the device configures a new trust state on all the physical ports that comprise the channel.

If you want DAI to use static IP-MAC address bindings to determine if ARP packets are valid, ensure that the DHCP snooping feature is enabled and that you have configured the static IP-MAC address bindings. For configuration information, see the "Configuring DHCP Snooping" section on page 11-7.

If you want DAI to use dynamic IP-MAC address bindings to determine if ARP packets are valid, ensure that DHCP snooping is configured (see the "Configuring DHCP Snooping" section on page 11-7).

For each device that you use DCNM to configure DAI, ensure that you configure the logging level for DHCP snooping to 6 (Informational) or a higher level. To configure the device with the minimal required logging configuration, log into the command-line interface of the device and use the following commands:

switch(config)# logging level dhcp 6
switch(config)# logging logfile messages 6
switch(config)# logging event link-status default

For more information about NX-OS system-message logging requirements, see the Cisco DCNM Fundamentals Configuration Guide, Release 4.1.

Configuring DAI

Figure 12-3 shows the ARP Inspection content pane.

Figure 12-3 ARP Inspection Pane

This section includes the following topics:

Enabling or Disabling DAI on VLANs

Configuring the DAI Trust State of a Layer 2 Interface

Applying ARP ACLs to VLANs for DAI Filtering

Enabling or Disabling Additional Validation

Configuring the DAI Logging Buffer Size

Configuring the DAI System Logging Rate

Configuring DAI Log Filtering

Enabling or Disabling DAI on VLANs

You can enable or disable DAI on VLANs.

BEFORE YOU BEGIN

By default, DAI is disabled on all VLANs.

If you are enabling DAI, ensure the following:

DHCP snooping is enabled. For more information, see the "Enabling or Disabling the DHCP Snooping Feature" section on page 11-8.

The VLANs on which you want to enable DAI are configured.

Ensure that you configure the logging level for DHCP snooping to 6 (Informational) or a higher level on the device. To configure the device with the minimal required logging configuration, log into the command-line interface of the device and use the following commands:

switch(config)# logging level dhcp 6
switch(config)# logging logfile messages 6
switch(config)# logging event link-status default

For more information about NX-OS system-message logging requirements, see the Cisco DCNM Fundamentals Configuration Guide, Release 4.1.

DETAILED STEPS

To enable or disable DAI on a VLAN, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device that has the VLAN that you want to configure with DAI.

The VLANs on the device appear in the Summary pane.

Step 3 From the Summary pane, click the VLAN that you want to configure with DAI.

The DAI VLAN Details tab appears in the Details pane.

Step 4 From the DAI VLAN Details tab, do one of the following:

To enable DAI on the selected VLAN, check ARP Inspection.

To disable DAI on the selected VLAN, uncheck ARP Inspection.

Step 5 From the menu bar, choose File > Deploy to apply your changes to the device.


Configuring the DAI Trust State of a Layer 2 Interface

You can configure the DAI interface trust state of a Layer 2 interface.

A device forwards ARP packets that it receives on a trusted Layer 2 interface but does not check them. For more information about DAI trust states, see the "Interface Trust States and Network Security" section.

On untrusted interfaces, the device intercepts all ARP requests and responses, verifies that the intercepted packets have valid IP-MAC address bindings before updating the local cache and forwarding the packet to the appropriate destination. If the device determines that packets have invalid bindings, it drops the packets and logs them according to the logging configuration. For more information, see the "Configuring DAI Log Filtering" section.

BEFORE YOU BEGIN

By default, all interfaces are untrusted.

If you are enabling DAI, ensure that DHCP snooping is enabled. For more information, see the "Enabling or Disabling the DHCP Snooping Feature" section on page 11-8.

DETAILED STEPS

To configure the DAI trust state of a Layer 2 interface, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device that has the Layer 2 interface whose DAI trust state you want to configure.

The Details tab appears in the Details pane.

Step 3 From the Details tab, expand the ARP Trust State section, if necessary.

A table of slots on the selected device appears in the ARP Trust State section.

Step 4 Double-click the slot that contains the Layer 2 interface that you want to configure.

The Layer 2 interfaces on the slot appear. For each interface, a check box in the Trust State column indicates whether the device trusts the interface.

Step 5 In the Trust State column for the interface that you want to configure, do one of the following:

To make the interface a trusted DAI interface, check or uncheck Trust State.

To make the interface an untrusted DAI interface, uncheck Trust State.

Step 6 From the menu bar, choose File > Deploy to apply your changes to the device.


Applying ARP ACLs to VLANs for DAI Filtering

You can apply an ARP ACL to one or more VLANs. The device permits packets only if the ACL permits them.

BEFORE YOU BEGIN

By default, no VLANs have an ARP ACL applied.

Ensure that the ARP ACL that you want to apply is correctly configured. For information about configuring an ARP ACL, see the "Configuring ARP ACLs" section.

DETAILED STEPS

To apply an ARP ACL to a VLAN for DAI filtering, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device that has the VLAN that you want to configure with an ARP ACL.

The VLANs on the device appear in the Summary pane.

Step 3 From the Summary pane, click the VLAN that you want to configure with an ARP ACL.

The DAI VLAN Details tab appears in the Details pane. On the DAI VLAN Details tab, the ARP ACL drop-down list appears.

Step 4 From the DAI VLAN Details tab, do one of the following:

To apply an ARP ACL to the VLAN, from the ARP ACL drop-down list, choose the ACL that you want to apply.

To remove an ARP ACL from the VLAN, from the menu bar, choose Actions > Remove ARP ACL from VLAN.

Step 5 From the menu bar, choose File > Deploy to apply your changes to the device.


Enabling or Disabling Additional Validation

You can enable or disable additional validation of ARP packets.

DAI intercepts, logs, and discards ARP packets with invalid IP-to-MAC address bindings. You can enable additional validation on the destination MAC address, the sender and target IP addresses, and the source MAC address.

BEFORE YOU BEGIN

By default, no additional validation of ARP packets is enabled.

DETAILED STEPS

To enable or disable additional validation, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device that you want to configure with additional validation.

The Details tab appears in the Details pane.

Step 3 From the Details tab, expand the Global Settings section, if necessary.

Step 4 (Optional) To enable or disable source MAC address validation, check or uncheck Source MAC Validation.

Step 5 (Optional) To enable or disable destination MAC address validation, check or uncheck Destination MAC Validation.

Step 6 (Optional) To enable or disable source and target IP address validation, check or uncheck IP Address Validation.

Step 7 From the menu bar, choose File > Deploy to apply your changes to the device.


Configuring the DAI Logging Buffer Size

You can configure the DAI logging buffer size.

BEFORE YOU BEGIN

The default buffer size is 32 messages.

DETAILED STEPS

To configuring the DAI logging buffer size, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device whose DAI logging buffer size you want to configure.

The Details tab appears in the Details pane.

Step 3 From the Details tab, expand the Global Settings section, if necessary.

The Total Buffer Size field appears in the Global Settings section.

Step 4 Click the Total Buffer Size field and enter the maximum number of DAI messages that the buffer can have.

Step 5 From the menu bar, choose File > Deploy to apply your changes to the device.


Configuring the DAI System Logging Rate


Note The DAI system logging rate is not configurable in NX-OS 4.1.


You can configure the DAI system logging rate.

BEFORE YOU BEGIN

The default DAI system logging rate is five messages every second.

DETAILED STEPS

To configure the DAI system logging rate, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, click the device whose DAI logging buffer size you want to configure.

The Details tab appears in the Details pane.

Step 3 From the Details tab, expand the Global Settings section, if necessary.

The Log Messages field and the Log Interval (sec) field appear in the Global Settings section. The device sends messages at the rate of the number of messages in the Log Messages field per the number of seconds in the Log Interval (sec) field.

Step 4 (Optional) Click the Log Messages field and enter the number of messages.

Step 5 (Optional) Click the Log Interval(sec) field and enter the number of seconds.

Step 6 From the menu bar, choose File > Deploy to apply your changes to the device.


Configuring DAI Log Filtering

You can configure how the device determines whether to log a DAI packet.

BEFORE YOU BEGIN

By default, the device logs DAI packets that are dropped.

DETAILED STEPS

To configure DAI log filtering, follow these steps:


Step 1 From the Feature Selector pane, choose Switching > Layer 2 Security > ARP Inspection.

The available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device that has the VLAN that you want to configure with DAI log filtering.

The VLANs on the device appear in the Summary pane.

Step 3 From the Summary pane, click the VLAN that you want to configure with DAI log filtering.

The DAI VLAN Details tab appears in the Details pane. On the DAI VLAN Details tab, the ACL Logging drop-down list and the DHCP Logging drop-down list appear.

Step 4 (Optional) From the ACL Logging drop-down list, choose the ACL logging option that you want.


Note The ACL Logging option is not supported in NX-OS 4.0.


Step 5 (Optional) From the DHCP drop-down list, choose the DHCP-binding logging option that you want.

Step 6 From the menu bar, choose File > Deploy to apply your changes to the device.


Displaying and Clearing DAI Statistics

A Statistics tab appears in the Details pane when you click a device or VLAN in the Summary pane. When a VLAN is selected, the Statistics tab displays information about DAI that is specific to that VLAN. When a device is selected, the Statistics tab displays information about DAI on all VLAN that are configured to perform DAI.

The following window appears in the Statistics tab:

DAI Statistics—Displays information about ARP packets processed.

See the Cisco DCNM Fundamentals Configuration Guide, Release 4.1 for more information on collecting statistics for this feature.

Field Descriptions for DAI

This section includes the following topics:

Device: Details: Global Settings Section

Device: Details: ARP Trust State Section

VLAN: DAI VLAN Details Tab

Related Fields

Device: Details: Global Settings Section

Table 12-1 Device: Details: Global Settings Section 

Field
Description

Source MAC Validation

Whether the device drops ARP packets when the source MAC address in the Ethernet header does not match the sender MAC address in the ARP message. This field applies to ARP requests and responses. By default, this check box is unchecked.

Destination MAC Validation

Whether the device drops ARP packets when the destination MAC address in the Ethernet header does not match the target MAC address in the ARP message. This field applies to ARP responses only. By default, this check box is unchecked.

IP Address Validation

Whether the device drops ARP packets that contain an invalid IP address for either the sender or target. This field applies to ARP requests and responses. By default, this check box is unchecked.

Total Buffer Size

Number of messages that the DAI log buffer can contain. By default, the buffer size is 64 messages.

Log Messages

Number of DAI log messages for the DAI logging rate limit. The device derives the limit by dividing the value in this field with the value in the Log Interval (sec) field. By default, the number of log messages in the rate limit is five.

Log Interval(sec)

Number of seconds for the DAI logging rate limit. The device derives the limit by dividing the value in the Log Messages field with the value in this field. By default, the number of seconds in the rate limit is 1.


Device: Details: ARP Trust State Section

Table 12-2 Device: Details: ARP Trust State Section 

Figure
Description

Interface

Display only. Name of the Layer 2 interface or the name of the slot containing Layer 2 interfaces.

Trust State

Whether the interface is trusted. When this check box is checked, the device does not trust ARP sources on the interface. By default, this check box is unchecked.


VLAN: DAI VLAN Details Tab

Table 12-3 VLAN: DAI VLAN Details Tab 

Figure
Description

VLAN

Display only. ID number of the VLAN.

VLAN Name

Display only. Name assigned to the VLAN. By default, VLAN 1 is named Default and all other VLANs are named by combining "VLAN" the four-digit VLAN ID. For example, the default VLAN name for VLAN 50 is VLAN0050.

ARP Inspection

Whether ARP inspection is enabled for the VLAN. When this check box is checked, the device inspects ARP packets received on the VLAN. By default, this check box is unchecked.

ARP ACL

Name of the ARP ACL applied to the VLAN. By default, this list is blank.

ACL Logging

Type of ARP ACL log filtering applied to ARP traffic on the VLAN.Valid options are as follows:

Match Log—Packets matching ARP ACL rules that have logging enabled are logged.

Deny—(Default) Denied ARP packets are logged.

None—No ARP packets are logged.

DHCP Logging

Type of logging for DHCP packets on the VLAN. Valid options are as follows:

Permit—Permitted DHCP packets are logged.

All—All DHCP packets are logged.

Deny—(Default) Denied packets are logged.

None—No DHCP packets are logged.

ARP Operational State

Display only. Whether ARP inspection is active on the interface.


Related Fields

For information about fields that configure ARP ACLs, see the "Field Descriptions for ARP ACLs" section.

Configuring ARP ACLs

Figure 12-4 shows the ARP ACL content pane.

Figure 12-4 ARP ACL Content Pane

This section includes the following topics:

Creating an ARP ACL

Changing an ARP ACL

Removing an ARP ACL

Creating an ARP ACL

You can create an ARP ACL on the device and add rules to it.

DETAILED STEPS

To create an ARP ACL on the device, follow these steps:


Step 1 From the Feature Selector pane, choose Security > Access Control > ARP ACL.

Available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device to which you want to add an ACL.

Step 3 From the menu bar, choose File > New > ACL.

A blank row appears in the Summary pane. The Details tab appears in the Details pane.

Step 4 On the Details tab, in the Name field, type a name for the ACL.

Step 5 For each rule or remark that you want to add to the ACL, from the menu bar, choose File > New and choose ACE or Remark. On the Details tab, configure fields as needed.


Note To log packets that match a rule, check Log, complete the procedure, and then confirm that DAI logging for each VLAN that you apply the ACL to is configured to log packets when they match a rule in the ARP ACL. For more information, see the "Configuring DAI Log Filtering" section.


Step 6 From the menu bar, choose File > Deploy to apply your changes to the device.


Changing an ARP ACL

You can change, reorder, add, and remove rules in an existing ARP ACL.

DETAILED STEPS

To change an ARP ACL, follow these steps:


Step 1 From the Feature Selector pane, choose Security > Access Control > ARP ACL.

Available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device that has the ACL that you want to change and then double-click the ACL.

The ACLs on the device and the rules of the ACL that you double-clicked appear in the Summary pane.

Step 3 (Optional) If you want to change the details of a rule, click the rule in the Summary pane. On the Details tab, configure fields as needed.


Note To log packets that match a rule, check Log, complete the procedure, and then confirm that DAI logging for each VLAN that you apply the ACL to is configured to log packets when they match a rule in the ARP ACL. For more information, see the "Configuring DAI Log Filtering" section.


Step 4 (Optional) If you want to add a rule or remark, click the ACL in the Summary pane and then from the menu bar, choose File > New and choose ACE or Remark. On the Details tab, configure fields as needed.

Step 5 (Optional) If you want to remove a rule, click the rule and then from the menu bar, choose ARP ACL > Delete.

Step 6 (Optional) If you want to move a rule or remark to a different position in the ACL, click the rule or remark and then from the menu bar, choose one of the following, as applicable:

ARP ACL > Move Up

ARP ACL > Move Down

The rule moves up or down, as you chose. The sequence number of the rules adjust accordingly.

Step 7 From the menu bar, choose File > Deploy to apply your changes to the device.


Removing an ARP ACL

You can remove an ARP ACL from the device.

BEFORE YOU BEGIN

Ensure that you know whether the ACL is applied to a VLAN. The device allows you to remove ACLs that are currently applied. Removing an ACL does not affect the configuration of VLANs where you have applied the ACL. Instead, the device considers the removed ACL to be empty.

DETAILED STEPS

To remove an ARP ACL from the device, follow these steps:


Step 1 From the Feature Selector pane, choose Security > Access Control > ARP ACL.

Available devices appear in the Summary pane.

Step 2 From the Summary pane, double-click the device from which you want to remove an ACL.

The ACLs currently on the device appear in the Summary pane.

Step 3 Click the ACL that you want to remove.

Step 4 From the menu bar, choose ARP ACL > Delete.

The ACL disappears from the Summary pane.

Step 5 From the menu bar, choose File > Deploy to apply your changes to the device.


Field Descriptions for ARP ACLs

This section includes the following topics:

ARP ACL: ACL Details Tab

ARP Access Rule: ACE Details Tab

ARP Access Rule: ACE Details: Source and Destination Section

ARP ACL Remark: Remark Details Tab

Related Fields

ARP ACL: ACL Details Tab

Table 12-4 ARP ACL: ACL Details Tab 

Field
Description

Name

Name of the ARP ACL. Names can be a maximum of 64 alphanumeric characters but must begin with an alphabetic character. No name is assigned by default.


ARP Access Rule: ACE Details Tab

Table 12-5 ARP Access Rule: ACE Details Tab 

Field
Description

Sequence No.

Sequence number of the rule. Must be a whole number between 1 and 4294967295. If you add a rule after another rule, the default sequence number is 10 greater than the preceding rule. If you add a rule before another rule, the number is 10 less than the following rule.

Action

Action taken by the device when it determines that the rule applies to the packet. Valid values are as follows:

Deny—Stops processing the packet and drop it.

Permit—Continues processing the packet. This is the default value.

Log

Whether the device logs statistics about traffic to which the access rule applies. This check box is unchecked by default.


ARP Access Rule: ACE Details: Source and Destination Section

Table 12-6 ARP Access Rule: ACE Details: Source and Destination Section 

Field
Description

ARP Packet Type

Type of ARP packet that the rule matches:

Response—The rule matches ARP responses only.

Both—(Default) The rule matches ARP response and request packets.

Request—The rule matches ARP requests only.

Sender

IP Type

IP address of the sender or, if Both is selected in the ARP Packet Type list, sender and target. You can choose one of the following radio buttons:

Any—The rule matches the selected ARP packet type from any IPv4 source. This is the default value.

Host—The rule matches the selected ARP packet type from a specific IPv4 address. When you select this radio button, the IP Address field appears.

Network—The rule matches the selected ARP packet type from an IPv4 network. When you select this radio button, the IP Address field and the Wildcard Mask field appear.

IP Address

IPv4 address of a host or a network. Valid addresses are in dotted decimal format. This field is available when you choose the Host radio button or the Network radio button. This field is unavailable by default.

Wildcard Mask (IP Type)

Wildcard mask of an IPv4 network. Valid masks are in dotted decimal format. For example, if you specified 192.168.0.0 in the IP Address field, you would enter 0.0.255.255 in this field. This field is available when you choose the Network radio button. This field is unavailable by default.

MAC Type

MAC address of sender or, if Both is selected in the ARP Packet Type list, sender and target. You can choose one of the following radio buttons:

Any—The rule matches the selected ARP packet type from any MAC source. This is the default value.

Host—The rule matches the selected ARP packet type from a specific MAC address. When you select this radio button, the MAC Address field appears.

Network—The rule matches the selected ARP packet type from a MAC network. When you select this radio button, the MAC Address field and the Wildcard Mask field appear.

MAC Address

MAC address of a host or a network. Valid addresses are in dotted hexadecimal format. This field is available when you choose the Host radio button or the Network radio button. This field is unavailable by default.

Wildcard Mask (MAC Type)

Wildcard mask of a MAC network. Valid masks are in dotted hexadecimal format. For example, if you specified 00c0.4f03.0000 in the MAC Address field, you would enter 0000.0000.ffff in this field. This field is available when you choose the Network radio button. This field is unavailable by default.

Target

IP Type

IP address of the target. You can choose one of the following radio buttons:

Any—The rule matches ARP response packets for any IPv4 target address. This is the default value.

Host—The rule matches ARP response packets for a specific IPv4 target address. When you select this radio button, the IP Address field appears.

Network—The rule matches ARP response packets for an IPv4 network. When you select this radio button, the IP Address field and the Wildcard Mask field appear.

IP Address

IPv4 address of a target host or a network. Valid addresses are in dotted decimal format. This field is available when you choose the Host radio button or the Network radio button. This field is unavailable by default.

Wildcard Mask (IP Type)

Wildcard mask of an IPv4 target network. Valid masks are in dotted decimal format. For example, if you specified 192.168.0.0 in the IP Address field, you would enter 0.0.255.255 in this field. This field is available when you choose the Network radio button. This field is unavailable by default.

MAC Type

MAC address of the target. You can choose one of the following radio buttons:

Any—The rule matches ARP response packets for any MAC target address. This is the default value.

Host—The rule matches ARP response packets for a specific target MAC address. When you select this radio button, the MAC Address field appears.

Network—The rule matches ARP response packets for a specific target MAC network. When you select this radio button, the MAC Address field and the Wildcard Mask field appear.

MAC Address

MAC address of a target host or a network. Valid addresses are in dotted hexadecimal format. This field is available when you choose the Host radio button or the Network radio button. This field is unavailable by default.

Wildcard Mask (MAC Type)

Wildcard mask of a target MAC network. Valid masks are in dotted hexadecimal format. For example, if you specified 00c0.4f03.0000 in the MAC Address field, you would enter 0000.0000.ffff in this field. This field is available when you choose the Network radio button. This field is unavailable by default.


ARP ACL Remark: Remark Details Tab

Table 12-7 ARP ACL Remark: Remark Details Tab 

Field
Description

Sequence No.

Sequence number of the remark. The number must be a whole number between 1 and 4294967295. If you add a rule after another rule, the default sequence number is 10 greater than the preceding rule. If you add a rule before another rule, the number is 10 less than the following rule.

Description

Remark text, up to 100 alphanumeric characters. By default, this field is empty.


Related Fields

For information about fields that apply ARP ACLs, see the "VLAN: DAI VLAN Details Tab" section.

Additional References

For additional information related to implementing DAI, see the following sections:

Related Documents

Standards

Related Documents

Related Topic
Document Title

DHCP snooping

Information About DHCP Snooping, page 11-1


Standards

Standards
Title

RFC-826

An Ethernet Address Resolution Protocol (http://tools.ietf.org/html/rfc826)


Feature History for DAI

Table 12-8 lists the release history for this feature.

Table 12-8 Feature History for DAI 

Feature Name
Releases
Feature Information

DAI

4.1(2)

No change from Release 4.0.