Specifying Black Hole Thresholds

A black hole threshold is a limit to the number of times a virtual router can retransmit identical sequences of datagrams before the retransmissions are identified as a problem.

Some domains might be configured not to generate certain ICMP messages (like an ICMP destination unreachable message) or to filter all ICMP messages. Under these conditions, the source of oversized ICMP packets never learns that it is sending oversized packets. The device continues sending oversized packets that never get through. This behavior is often referred to as a black hole.

tcp path-mtu-discovery black-hole-detect-threshold

• Use to specify the minimum MTU value used for the path MTU. If the discovered PMTU value is less than the minimum setting, path MTU discovery is disabled for this connection.
• Example

  host1:VR1(config)#tcp path-mtu-discovery black-hole-detect-threshold 200

• Use the no version to disable black hole threshold detection.
• See tcp path-mtu-discovery

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