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CLI-based Configuration Guide - Security

AR500, AR510, and AR530 V200R007

This document describes the configurations of Security, including AAA, DAA,NAC, BRAS Access, ACL, Firewall, Deep Security Defense, Local Attack Defense;Attack Defense, Traffic Suppression, ARP Security, Port Security, DHCP Snooping, IPSG, URPF, PKI, SSL, HTTPS, Keychain, separating the management plane from the service plane, security risks.
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Configuring Defense Against DHCP Server DoS Attacks

Configuring Defense Against DHCP Server DoS Attacks

Context

Malicious use of IP addresses exhausts IP addresses in the IP address pool, so authorized users cannot obtain IP addresses. The DHCP server generally identifies the MAC address of a DHCP client based on the CHADDR (client hardware address) field in the DHCP Request message. If attackers continuously apply for IP addresses by changing the CHADDR field, IP addresses in the address pool on the DHCP server may be exhausted. As a result, authorized users cannot obtain IP addresses.

To prevent DHCP users on some interfaces from applying IP addresses maliciously, 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 attackers from 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. If the two values match, the message is forwarded; if the two values do not match, the message is discarded.

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-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.

      By default, a maximum of 128 DHCP snooping binding entries can be learned on an interface.

  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: 2019-05-25

Document ID: EDOC1000097287

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