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Configuration Guide - IP Service
S1720, S2700, S5700, and S6720 V200R011C10

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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Setting the Aging Time of Dynamic PMTU

Setting the Aging Time of Dynamic PMTU


When the device functions as a source node and sends packets to a destination node, the device dynamically negotiates the PMTU with the destination node according to the IPv6 MTU values of interfaces and fragments packets based on the PMTU. After the PMTU ages out, the dynamic PMTU is deleted. The source node dynamically renegotiates the PMTU with the destination node.

When both static and dynamic PMTUs are configured, only static PMTU takes effect. Static PMTU entries never age.

The interface MTU, IPv6 interface MTU, and PMTU are valid only for packets generated on the device, not for packets forwarded by the host.


  1. Run system-view

    The system view is displayed.

  2. (Optional) Configure the IPv6 MTU for an interface.

    1. Run interface interface-type interface-number

      The specified interface view is displayed.

    2. (Optional) On an Ethernet interface, run undo portswitch

      The interface is switched to Layer 3 mode.

      By default, an Ethernet interface works in Layer 2 mode.

      Only the S5720HI, S5720EI, S6720EI, and S6720S-EI support switching between Layer 2 and Layer 3 modes.

    3. Run ipv6 enable

      The IPv6 function is enabled on the interface.

      By default, the IPv6 function is disabled on an interface.

    4. Run ipv6 mtu mtu

      The MTU of IPv6 packets on an interface is set.

      By default, the MTU of IPv6 packets on an interface is 1500 bytes.

      The switch supports MTU setting, so packets sent by the protocol stack are fragmented based on the configured MTU. However, the hardware chip does not support MTU setting, and the default MTU is 12K.

      After the MTU value is changed, run the shutdown and undo shutdown commands or the restart (interface view) command to restart the interface and allow the changes to take effect.

    5. Run quit

      Return to the system view.

  3. Run ipv6 pathmtu age age-time

    The aging time is set for dynamic PMTU entries.

    By default, the aging time of dynamic PMTU entries is 10 minutes.

Updated: 2020-02-26

Document ID: EDOC1000178170

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