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Configuration Guide - IP Service

S1720, S2700, S5700, and S6720 V200R012(C00 and C20)

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DHCP policy VLAN, DNS, mDNS gateway, mDNS relay, UDP Helper, IP performance optimization, IPv6, DHCPv6, IPv6 DNS, IPv6 over IPv4 tunnel, and IPv4 over IPv6 tunnel.
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(Optional) Disabling the Function of Checking Abnormal Packets

(Optional) Disabling the Function of Checking Abnormal Packets

Context

Devices from different vendors may use different DHCP implementation mechanisms. After checking the UDP header checksum or magic-cookie field in a received DHCP packet, a device may not allow the DHCP packet to pass through and discards the packet. As a result, DHCP becomes unavailable. To solve this problem, you can disable the function of checking abnormal packets to allow the device to properly forward a DHCP packet with an incorrect UDP header checksum or an incorrect value in the magic-cookie field.

NOTE:
  • This function applies to DHCP servers, DHCP relay agents, DHCP clients, and DHCP snooping-enabled devices.
  • After DHCP is enabled, the device checks the IP header checksum and UDP header checksum of DHCP messages by default, and the function of checking the IP header checksum cannot be disabled.

Procedure

  • Disable the function of checking abnormal packets in the system view.
    1. Run system-view

      The system view is displayed.

    2. The function of checking abnormal packets is disabled.

      • Run undo dhcp anti-attack check magic-cookie

        The function of checking the magic-cookie field in a DHCP packet is disabled.

        By default, a device does not check the magic-cookie field in a DHCP packet but directly forwards a DHCP packet with an incorrect value in the magic-cookie field.

      • Run undo dhcp anti-attack check udp-checksum

        The function of checking the UDP header checksum in a DHCP packet is disabled.

        By default, a device checks the UDP header checksum in a DHCP packet and discards a DHCP packet with an incorrect checksum.

  • Disable the function of checking abnormal packets in the VLAN view.
    1. Run system-view

      The system view is displayed.

    2. Run vlan vlan-id

      The VLAN view is displayed.

    3. Disable the function of checking abnormal packets.

      • Run undo dhcp anti-attack check magic-cookie

        The function of checking the magic-cookie field in a DHCP packet is disabled.

        By default, a device does not check the magic-cookie field in a DHCP packet but directly forwards a DHCP packet with an incorrect value in the magic-cookie field.

      • Run undo dhcp anti-attack check udp-checksum

        The function of checking the UDP header checksum in a DHCP packet is disabled.

        By default, a device checks the UDP header checksum in a DHCP packet and discards a DHCP packet with an incorrect checksum.

  • Disable the function of checking abnormal packets in the interface view.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. The function of checking abnormal packets is disabled.

      • Run undo dhcp anti-attack check magic-cookie

        The function of checking the magic-cookie field in a DHCP packet is disabled.

        By default, a device does not check the magic-cookie field in a DHCP packet but directly forwards a DHCP packet with an incorrect value in the magic-cookie field.

      • Run undo dhcp anti-attack check udp-checksum

        The function of checking the UDP header checksum in a DHCP packet is disabled.

        By default, a device checks the UDP header checksum in a DHCP packet and discards a DHCP packet with an incorrect checksum.

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Updated: 2018-12-24

Document ID: EDOC1100038342

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