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XIV. Miscellaneous Questions

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What is the MTU and MSS and how do I change it ?

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Products:
Vigor 2135ax
Vigor 2620Ln
Vigor 2760
Vigor 2762
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Keywords:
MSS
MTU
Maximum Transmission Unit
Packet Size
  • MRU - Maximum Receive Unit sets the maximum size acceptable to this device for any single PPP packet received. If a packet is larger than this value, the packet is fragmented (broken into smaller packets) before transmission.. The value is used at the start of the PPP negotiation.
  • MTU - Maximum Transmit Unit sets the maximum size for any single PPP packet that will be transmitted by this device. If a packet is larger than this value, the packet is fragmented (broken into smaller packets) before transmission. The value is used at the start of the PPP negotiation.
  • MSS - Maximum Segment Size is the largest size of data that TCPwill send in a single IP packet. A TCP/IP header is 40 bytes, so the MSS should be at least 40 bytes lower than the peers' MTUs.

    The Vigor sets its MSS deducting 40 from the value set by the ppp_mss command (see later).

    To check the current MSS/MTU setting on your Vigor router, telnet to the router and then enter :

    Vigor> wan ppp_mss ?
Now : 1442

    The above example shows the current value is set to 1442. To change it :

    Vigor> wan ppp_mss 1500
Now : 1500

    You can then reboot your router; the setting is retained after power-down or reboot.

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First Published: 18/03/2013
Last Updated: 22/04/2021

Comments

From: BookIT
24/08/2018

My 2860ac doesn't have a "wan ppp_mss" command. Does have "wan mtu" which does what above describes "wan ppp_mss" doing. Above does not say how to set MRU, command is "wan ppp_mru"