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CLI-based Configuration Guide - Security

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document provides the basic concepts, configuration procedures, and configuration examples in different application scenarios of the network management feature supported by the device.
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Configuring Defense Against DHCP Server DoS Attacks

Configuring Defense Against DHCP Server DoS Attacks

Context

If attackers maliciously apply for IP addresses from the DHCP server, the IP address pool becomes exhausted, preventing authorized users from obtaining IP addresses. This can happen if attackers continuously apply for IP addresses by changing the client hardware address (CHADDR) field, which is the field that DHCP servers generally use to identify the MAC address of a DHCP client.

To prevent DHCP users on some interfaces from maliciously applying for IP addresses, you can limit the number of DHCP snooping binding entries that can be learned by an interface. When the number of DHCP snooping binding entries reaches the maximum value, no DHCP client can obtain an IP address through the interface. To prevent attacks carried out by continuously changing the CHADDR field in the DHCP Request message, enable the device to check whether the MAC address in the Ethernet frame header matches the CHADDR field in the DHCP message. With this function enabled, the message is only forwarded if the two values match.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Set the maximum number of DHCP snooping binding entries to be learned by an interface in the VLAN, or interface view.
    1. Run vlan vlan-id

      The VLAN view is displayed.

      Or run interface interface-type interface-number

      The interface view is displayed.

    2. Run dhcp snooping max-user-number max-user-number

      The maximum number of DHCP snooping binding entries is set on the interface.

      If you run this command in the VLAN view, the command takes effect for all the interfaces in the VLAN.

  3. Enable the device to check the CHADDR field in the message in the VLAN view or interface view.
    1. Run vlan vlan-id

      The VLAN view is displayed.

      Or run interface interface-type interface-number

      The interface view is displayed.

    2. Run dhcp snooping check mac-address enable

      The device is enabled to check whether the MAC address in the Ethernet frame header matches the CHADDR field in the DHCP message.

      By default, the device does not check whether the MAC address in the Ethernet frame header matches the CHADDR field in the DHCP message.

      If you run the dhcp snooping check mac-address enable command in the VLAN view, the command takes effect on all the DHCP messages in the specified VLAN received by all the interfaces on the device. If you run the dhcp snooping check mac-address enable command in the interface view, the command takes effect for all the DHCP messages received on the interface.

    3. Run quit

      Return to the system view.

  4. (Optional) Set the alarm threshold for the number of messages discarded by DHCP snooping in the system view or interface view.

    • In the system view:

    1. Run dhcp snooping alarm threshold threshold

      The global alarm threshold for the number of discarded messages by DHCP snooping is set.

      If you run this command in the system view, the command takes effect for all the interfaces on the device.

      By default, the global alarm threshold for the number of messages discarded by DHCP snooping is 100.

    • In the interface view:

    1. Run interface interface-type interface-number

      The interface view is displayed.

    2. Run dhcp snooping alarm mac-address threshold threshold

      The alarm threshold for the number of DHCP messages discarded because the CHADDR field in the DHCP messages does not match the source MAC address in the Ethernet frame header is set.

      By default, an alarm is generated in the system when at least 100 DHCP snooping messages are discarded, and the alarm threshold on an interface is set using the dhcp snooping alarm threshold command in the system view.

      NOTE:

      If the alarm threshold is set in the system view and interface view, the smaller value takes effect.

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Updated: 2019-08-07

Document ID: EDOC1100034077

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