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

Table 28: 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

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