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    Monitoring TCP PMTU Information

    Purpose

    Display PMTU information.

    Action

    To display PMTU information:

    host1#show tcp path-mtu-discovery 
    TCP PMTU Discovery is ENABLED
        Administrative Minimum MTU: 512
        Administrative Maximum MTU: 65535
        Timer 1: 10 minutes
        Timer 2: 2 minutes
    Black Hole Detect Threshold: 0 retransmissions
    # ICMP TooBigs: 0
    # ICMP TooBigs for unk. connections: 0

    Meaning

    Table 1 lists the show tcp path-mtu-discovery command output fields.

    Table 1: show tcp path-mtu-discovery Output Fields

    Field Name

    Field Description

    TCP PMTU Discovery

    State of the PMTUD functions (ENABLED or DISABLED)

    Administrative Minimum MTU

    Administrative minimum PMTU that is supported or none if there is no minimum

    Administrative Maximum MTU

    Administrative maximum PMTU that is supported or none if there is no maximum

    Timer 1

    Value of timer 1 in minutes

    Timer 2

    Value of timer 2 in minutes

    Black Hole Detect Threshold

    Number of retransmissions allowed before TCP/PMTUD assumes that there is a black hole and attempts to reduce impact in the MSS

    # ICMP TooBigs

    Number of ICMP Too Big messages that have been received

    # ICMP TooBigs for unk. connections

    Number of ICMP Too Big messages that have been received which were not for a valid connection

    Published: 2014-08-13