The device can provide multiple features to detect and prevent ARP attacks and viruses in the LAN. An attacker can exploit ARP vulnerabilities to attack network devices in the following ways:

· Sends a large number of unresolvable IP packets to have the receiving device busy with resolving IP addresses until its CPU is overloaded. Unresolvable IP packets refer to IP packets for which ARP cannot find corresponding MAC addresses.

· Sends a large number of ARP packets to overload the CPU of the receiving device.

· Acts as a trusted user or gateway to send ARP packets so the receiving devices obtain incorrect ARP entries.

ARP attack protection tasks at a glance

All ARP attack protection tasks are optional.

· Preventing flood attacks

¡ Configuring unresolvable IP attack protection

¡ Configuring source MAC-based ARP attack detection

· Preventing user and gateway spoofing attacks

¡ Configuring ARP packet source MAC consistency check

¡ Configuring ARP active acknowledgement

¡ Configuring authorized ARP

¡ Configuring ARP scanning and fixed ARP

¡ Configuring ARP gateway protection

¡ Configuring ARP filtering

Configuring unresolvable IP attack protection

About unresolvable IP attack protection

If a device receives a large number of unresolvable IP packets from a host, the following situations can occur:

· The device sends a large number of ARP requests, overloading the target subnets.

· The device keeps trying to resolve the destination IP addresses, overloading its CPU.

To protect the device from such IP attacks, you can configure the following features:

· ARP source suppression—Stops resolving packets from an IP address if the number of unresolvable IP packets from the IP address exceeds the upper limit within 5 seconds. The device continues ARP resolution when the interval elapses. This feature is applicable if the attack packets have the same source addresses.

· ARP blackhole routing—Creates a blackhole route destined for an unresolved IP address. The device drops all matching packets until the blackhole route is deleted. A blackhole route is deleted when its aging timer is reached or the route becomes reachable.

After a blackhole route is created for an unresolved IP address, the device immediately starts the first ARP blackhole route probe by sending an ARP request. If the resolution fails, the device continues probing according to the probe settings. If the IP address resolution succeeds in a probe, the device converts the blackhole route to a normal route. If an ARP blackhole route ages out before the device finishes all probes, the device deletes the blackhole route and does not perform the remaining probes.

This feature is applicable regardless of whether the attack packets have the same source addresses.

Configuring ARP source suppression

1. Enter system view.

system-view

2. Enable ARP source suppression.

arp source-suppression enable

By default, ARP source suppression is disabled.

3. Set the maximum number of unresolvable packets that the device can process per source IP address within 5 seconds.

arp source-suppression limit limit-value

By default, the maximum number is 10.

Configuring ARP blackhole routing

Restrictions and guidelines

Set the ARP blackhole route probe count to a big value, for example, 25. If the device fails to reach the destination IP address temporarily and the probe count is too small, all probes might finish before the problem is resolved. As a result, non-attack packets will be dropped. This setting can avoid such situation.

Procedure

4. Enter system view.

system-view

5. Enable ARP blackhole routing.

arp resolving-route enable

By default, ARP blackhole routing is enabled.

6. (Optional.) Set the number of ARP blackhole route probes for each unresolved IP address.

arp resolving-route probe-count count

The default setting is three probes.

7. (Optional.) Set the interval at which the device probes ARP blackhole routes.

arp resolving-route probe-interval interval

The default setting is 1 second.

Display and maintenance commands for unresolvable IP attack protection

Execute display commands in any view.

Task	Command
Display ARP source suppression configuration information.	display arp source-suppression

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Example: Configuring unresolvable IP attack protection

Network configuration

As shown in Figure 1, a LAN contains two areas: an R&D area in VLAN 10 and an office area in VLAN 20. Each area connects to the gateway (Device) through an access switch.

A large number of ARP requests are detected in the office area and are considered an attack caused by unresolvable IP packets. To prevent the attack, configure ARP source suppression or ARP blackhole routing.

Figure 1 Network diagram

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Procedure

· If the attack packets have the same source address, configure ARP source suppression:

# Enable ARP source suppression.

<Device> system-view

[Device] arp source-suppression enable

# Configure the device to process a maximum of 100 unresolvable packets per source IP address within 5 seconds.

[Device] arp source-suppression limit 100

· If the attack packets have different source addresses, configure ARP blackhole routing:

# Enable ARP blackhole routing.

[Device] arp resolving-route enable

Configuring source MAC-based ARP attack detection

About source MAC-based ARP attack detection

This feature checks the number of ARP packets delivered to the CPU. If the number of packets from the same MAC address within 5 seconds exceeds a threshold, the device generates an ARP attack entry for the MAC address. If the ARP logging feature is enabled, the device handles the attack by using either of the following methods before the ARP attack entry ages out:

· Monitor—Only generates log messages.

· Filter—Generates log messages and filters out subsequent ARP packets from the MAC address.

To enable the ARP logging feature, use the arp check log enable command. For information about the ARP logging feature, see ARP configuration in Layer 3—IP Services Configuration Guide.

When an ARP attack entry ages out, ARP packets sourced from the MAC address in the entry can be processed correctly.

Restrictions and guidelines

When you change the handling method from monitor to filter, the configuration takes effect immediately. When you change the handling method from filter to monitor, the device continues filtering packets that match existing attack entries.

You can exclude the MAC addresses of some gateways and servers from this detection. This feature does not inspect ARP packets from those devices even if they are attackers.

Procedure

8. Enter system view.

system-view

9. Enable source MAC-based ARP attack detection and specify the handling method.

arp source-mac { filter | monitor }

By default, this feature is disabled.

10. Set the threshold.

arp source-mac threshold threshold-value

By default, the threshold for source MAC-based ARP attack detection is 30.

11. Set the aging timer for ARP attack entries.

arp source-mac aging-time time

By default, the lifetime is 300 seconds.

12. (Optional.) Exclude specific MAC addresses from this detection.

arp source-mac exclude-mac mac-address&<1-10>

By default, no MAC address is excluded.

Display and maintenance commands for source MAC-based ARP attack detection

Execute display commands in any view.

Task	Command
Display ARP attack entries detected by source MAC-based ARP attack detection.	In standalone mode: display arp source-mac { interface interface-type interface-number \| slot slot-number } In IRF mode: display arp source-mac { chassis chassis-number slot slot-number \| interface interface-type interface-number }

Task

Command

Display ARP attack entries detected by source MAC-based ARP attack detection.

In standalone mode:

display arp source-mac { interface interface-type interface-number | slot slot-number }

In IRF mode:

display arp source-mac { chassis chassis-number slot slot-number | interface interface-type interface-number }

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Example: Configuring source MAC-based ARP attack detection

Network configuration

As shown in Figure 2, the hosts access the Internet through a gateway (Device). If malicious users send a large number of ARP requests to the gateway, the gateway might crash and cannot process requests from the clients. To solve this problem, configure source MAC-based ARP attack detection on the gateway.

Figure 2 Network diagram

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Procedure

# Enable source MAC-based ARP attack detection, and specify the handling method as filter.

<Device> system-view

[Device] arp source-mac filter

# Set the threshold to 30.

[Device] arp source-mac threshold 30

# Set the lifetime for ARP attack entries to 60 seconds.

[Device] arp source-mac aging-time 60

# Exclude MAC address 0012-3f86-e94c from this detection.

[Device] arp source-mac exclude-mac 0012-3f86-e94c

Configuring ARP packet source MAC consistency check

About this task

This feature enables a gateway to filter out ARP packets whose source MAC address in the Ethernet header is different from the sender MAC address in the message body. This feature allows the gateway to learn correct ARP entries.

Procedure

13. Enter system view.

system-view

14. Enable ARP packet source MAC address consistency check.

arp valid-check enable

By default, ARP packet source MAC address consistency check is disabled.

Configuring ARP active acknowledgement

About this task

Use the ARP active acknowledgement feature on gateways to prevent user spoofing.

This feature enables the device to perform active acknowledgement before creating an ARP entry.

· Upon receiving an ARP request that requests the MAC address of the device, the device sends an ARP reply. Then, it sends an ARP request for the sender IP address in the received ARP request to determine whether to create an ARP entry for the sender IP address.

¡ If the device receives an ARP reply within the probe interval, it creates the ARP entry.

¡ If the device does not receive an ARP reply within the probe interval, it does not create the ARP entry.

· Upon receiving an ARP reply, the device examines whether it was the reply to the request that the device has sent.

¡ If it was, the device creates an ARP entry for the sender IP address in the ARP reply.

¡ If it was not, the device sends an ARP request for the sender IP address to determine whether to create an ARP entry for the sender IP address.

- If the device receives an ARP reply within the probe interval, it creates the ARP entry.

- If the device does not receive an ARP reply within the probe interval, it does not create the ARP entry.

To improve validity and reliability of ARP entries, you can enable ARP active acknowledgement in strict mode. In this mode, the device creates ARP entries only for the IP addresses that the device actively initiates the ARP resolution.

Procedure

15. Enter system view.

system-view

16. Enable the ARP active acknowledgement feature.

arp active-ack [ strict ] enable

By default, this feature is disabled.

For ARP active acknowledgement to take effect in strict mode, make sure ARP blackhole routing is enabled.

Configuring authorized ARP

About authorized ARP

Authorized ARP entries are generated based on the DHCP clients' address leases on the DHCP server or dynamic client entries on the DHCP relay agent. For more information about DHCP server and DHCP relay agent, see Layer 3—IP Services Configuration Guide.

Use this feature to prevent user spoofing and to allow only authorized clients to access network resources.

Procedure

17. Enter system view.

system-view

18. Enter interface view.

interface interface-type interface-number

Supported interface types include Layer 3 Ethernet interface, Layer 3 Ethernet subinterface, Layer 3 aggregate interface, Layer 3 aggregate subinterface, and VLAN interface.

19. Enable authorized ARP on the interface.

arp authorized enable

By default, authorized ARP is disabled.

Example: Configuring authorized ARP on a DHCP server

Network configuration

As shown in Figure 3, configure authorized ARP on GigabitEthernet 1/0/1 of Device A (a DHCP server) to ensure user validity.

Figure 3 Network diagram

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Procedure

20. Configure Device A:

# Specify the IP address for GigabitEthernet 1/0/1.

<DeviceA> system-view

[DeviceA] interface gigabitethernet 1/0/1

[DeviceA-GigabitEthernet1/0/1] ip address 10.1.1.1 24

[DeviceA-GigabitEthernet1/0/1] quit

# Configure DHCP.

[DeviceA] dhcp enable

[DeviceA] dhcp server ip-pool 1

[DeviceA-dhcp-pool-1] network 10.1.1.0 mask 255.255.255.0

[DeviceA-dhcp-pool-1] quit

# Enter Layer 3 Ethernet interface view.

[DeviceA] interface gigabitethernet 1/0/1

# Enable authorized ARP.

[DeviceA-GigabitEthernet1/0/1] arp authorized enable

[DeviceA-GigabitEthernet1/0/1] quit

21. Configure Device B:

<DeviceB> system-view

[DeviceB] interface gigabitethernet 1/0/1

[DeviceB-GigabitEthernet1/0/1] ip address dhcp-alloc

[DeviceB-GigabitEthernet1/0/1] quit

Verifying the configuration

# Display authorized ARP entry information on Device A.

[DeviceA] display arp all

Type: S-Static D-Dynamic O-Openflow R-Rule M-Multiport I-Invalid

IP address MAC address VLAN/VSI name Interface/Link ID Aging Type

10.1.1.2 0012-3f86-e94c -- GE1/0/1 20 D

The output shows that IP address 10.1.1.2 has been assigned to Device B.

Device B must use the IP address and MAC address in the authorized ARP entry to communicate with Device A. Otherwise, the communication fails. Thus user validity is ensured.

Example: Configuring authorized ARP on a DHCP relay agent

Network configuration

As shown in Figure 4, configure authorized ARP on GigabitEthernet 1/0/2 of Device B (a DHCP relay agent) to ensure user validity.

Figure 4 Network diagram

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Procedure

22. Configure Device A:

# Specify the IP address for GigabitEthernet 1/0/1.

<DeviceA> system-view

[DeviceA] interface gigabitethernet 1/0/1

[DeviceA-GigabitEthernet1/0/1] ip address 10.1.1.1 24

[DeviceA-GigabitEthernet1/0/1] quit

# Configure DHCP.

[DeviceA] dhcp enable

[DeviceA] dhcp server ip-pool 1

[DeviceA-dhcp-pool-1] network 10.10.1.0 mask 255.255.255.0

[DeviceA-dhcp-pool-1] gateway-list 10.10.1.1

[DeviceA-dhcp-pool-1] quit

[DeviceA] ip route-static 10.10.1.0 24 10.1.1.2

23. Configure Device B:

# Enable DHCP.

<DeviceB> system-view

[DeviceB] dhcp enable

# Specify the IP addresses of GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2.

[DeviceB] interface gigabitethernet 1/0/1

[DeviceB-GigabitEthernet1/0/1] ip address 10.1.1.2 24

[DeviceB-GigabitEthernet1/0/1] quit

[DeviceB] interface gigabitethernet 1/0/2

[DeviceB-GigabitEthernet1/0/2] ip address 10.10.1.1 24

# Enable DHCP relay agent on GigabitEthernet 1/0/2.

[DeviceB-GigabitEthernet1/0/2] dhcp select relay

# Add the DHCP server 10.1.1.1 to DHCP server group 1.

[DeviceB-GigabitEthernet1/0/2] dhcp relay server-address 10.1.1.1

# Enable authorized ARP.

[DeviceB-GigabitEthernet1/0/2] arp authorized enable

[DeviceB-GigabitEthernet1/0/2] quit

# Enable recording of relay entries on the relay agent.

[DeviceB] dhcp relay client-information record

24. Configure Device C:

<DeviceC> system-view

[DeviceC] ip route-static 10.1.1.0 24 10.10.1.1

[DeviceC] interface gigabitethernet 1/0/2

[DeviceC-GigabitEthernet1/0/2] ip address dhcp-alloc

[DeviceC-GigabitEthernet1/0/2] quit

Verifying the configuration

# Display authorized ARP information on Device B.

[DeviceB] display arp all

Type: S-Static D-Dynamic O-Openflow R-Rule M-Multiport I-Invalid

IP address MAC address VLAN/VSI name Interface/Link ID Aging Type

10.10.1.2 0012-3f86-e94c -- GE1/0/2 20 D

The output shows that Device A assigned the IP address 10.10.1.2 to Device C.

Device C must use the IP address and MAC address in the authorized ARP entry to communicate with Device B. Otherwise, the communication fails. Thus the user validity is ensured.

Configuring ARP scanning and fixed ARP

About this task

ARP scanning is typically used together with the fixed ARP feature in small-scale and stable networks.

ARP scanning automatically creates ARP entries for devices in an address range. The device performs ARP scanning in the following steps:

25. Sends ARP requests for each IP address in the address range.

26. Obtains their MAC addresses through received ARP replies.

27. Creates dynamic ARP entries.

Fixed ARP converts existing dynamic ARP entries (including those generated through ARP scanning) to static ARP entries. These static ARP entries are of the same attributes as the ARP entries that are manually configured. This feature prevents ARP entries from being modified by attackers.

Restrictions and guidelines

IP addresses in existing ARP entries are not scanned.

ARP scanning will take some time. To stop an ongoing scan, press Ctrl + C. Dynamic ARP entries are created based on ARP replies received before the scan is terminated.

Due to the limit on the total number of static ARP entries, some dynamic ARP entries might fail the conversion.

The arp fixup command is a one-time operation. You can use this command again to convert the dynamic ARP entries learned later to static.

To delete a static ARP entry converted from a dynamic one, use the undo arp ip-address [ vpn-instance-name ] command. You can also use the reset arp all command to delete all ARP entries or the reset arp static command to delete all static ARP entries.

Procedure

28. Enter system view.

system-view

29. Enter interface view.

interface interface-type interface-number

30. Trigger an ARP scanning.

arp scan [ start-ip-address to end-ip-address ]

31. Return to system view.

quit

32. Convert existing dynamic ARP entries to static ARP entries.

arp fixup

Configuring ARP gateway protection

About ARP gateway protection

Configure this feature on interfaces not connected with a gateway to prevent gateway spoofing attacks.

When such an interface receives an ARP packet, it checks whether the sender IP address in the packet is consistent with that of any protected gateway. If yes, it discards the packet. If not, it handles the packet correctly.

Restrictions and guidelines

You can enable ARP gateway protection for a maximum of eight gateways on an interface.

Do not configure both the arp filter source and arp filter binding commands on an interface.

If ARP gateway protection works with ARP attack detection, ARP snooping, and ARP fast-reply, ARP gateway protection applies first.

Procedure

33. Enter system view.

system-view

34. Enter interface view.

interface interface-type interface-number

Supported interface types include Layer 2 Ethernet interface and Layer 2 aggregate interface.

35. Enable ARP gateway protection for the specified gateway.

arp filter source ip-address

By default, ARP gateway protection is disabled.

Example: Configuring ARP gateway protection

Network configuration

As shown in Figure 5, Host B launches gateway spoofing attacks to Device B. As a result, traffic that Device B intends to send to Device A is sent to Host B.

Configure Device B to block such attacks.

Figure 5 Network diagram

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Procedure

# Configure ARP gateway protection on Device B.

<DeviceB> system-view

[DeviceB] interface gigabitethernet 1/0/1

[DeviceB-GigabitEthernet1/0/1] arp filter source 10.1.1.1

[DeviceB-GigabitEthernet1/0/1] quit

[DeviceB] interface gigabitethernet 1/0/2

[DeviceB-GigabitEthernet1/0/2] arp filter source 10.1.1.1

Verifying the configuration

# Verify that GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 discard the incoming ARP packets whose sender IP address is the IP address of the gateway.

Configuring ARP filtering

ARP filtering

The ARP filtering feature can prevent gateway spoofing and user spoofing attacks.

An interface enabled with this feature checks the sender IP and MAC addresses in a received ARP packet against permitted entries. If a match is found, the packet is handled correctly. If not, the packet is discarded.

Restrictions and guidelines

You can configure a maximum of eight permitted entries on an interface.

Do not configure both the arp filter source and arp filter binding commands on an interface.

If ARP filtering works with ARP attack detection, ARP snooping, and ARP fast-reply, ARP filtering applies first.

Procedure

36. Enter system view.

system-view

37. Enter interface view.

interface interface-type interface-number

Supported interface types include Ethernet interface and Layer 2 aggregate interface.

38. Enable ARP filtering and configure a permitted entry.

arp filter binding ip-address mac-address

By default, ARP filtering is disabled.

Example: Configuring ARP filtering

Network configuration

As shown in Figure 6, the IP and MAC addresses of Host A are 10.1.1.2 and 000f-e349-1233, respectively. The IP and MAC addresses of Host B are 10.1.1.3 and 000f-e349-1234, respectively.

Configure ARP filtering on GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 of Device B to permit ARP packets from only Host A and Host B.

Figure 6 Network diagram

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Procedure

# Configure ARP filtering on Device B.

<DeviceB> system-view

[DeviceB] interface gigabitethernet 1/0/1

[DeviceB-GigabitEthernet1/0/1] arp filter binding 10.1.1.2 000f-e349-1233

[DeviceB-GigabitEthernet1/0/1] quit

[DeviceB] interface gigabitethernet 1/0/2

[DeviceB-GigabitEthernet1/0/2] arp filter binding 10.1.1.3 000f-e349-1234

Verifying the configuration

# Verify that GigabitEthernet 1/0/1 permits ARP packets from Host A and discards other ARP packets.

# Verify that GigabitEthernet 1/0/2 permits ARP packets from Host B and discards other ARP packets.

12-Security Configuration Guide

Configuring ARP attack protection

Configuring unresolvable IP attack protection

Restrictions and guidelines

Procedure

Example: Configuring unresolvable IP attack protection

Network configuration

Procedure

Configuring source MAC-based ARP attack detection

Network configuration

Procedure

About this task

Procedure

About this task

Procedure

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Configuring ARP scanning and fixed ARP

About this task

Restrictions and guidelines

Procedure

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

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