Finisar Surveyor manual Icmp Fragmentation Needed D/F set

Expert Features 10

Network Layer

ICMP Fragmentation Needed [D/F set]

Counter

ICMP Fragmentation Needed [D/F set] events are counted in the ICMP All Errors and the ICMP Destination Unreachable counters. A count of all destination unreachable ICMP symptoms and a count of all ICMP errors displays in the Overview counters of Expert View. A threshold can be set in Expert Alarms for all destination unreachable ICMP errors or for all ICMP errors.

Expert Symptom

ICMP Fragmentation Needed [D/F] set events are automatically logged as expert symptoms. The Symptom Summary field provides information about the IP addresses involved. For example:

MTU of next Hop=2 to reach [206.250.228.69]. Cannot be

reached by [206.250.228.11] as D/F Set.

SA=[206.250.228.11] DA=[206.250.228.69]

Diagnostic Details

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Problem Description:

An ICMP Destination (Fragmentation needed, but, D/F set) Unreachable message has been sent.

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Probable Cause(s):

1.If a router has a routing table problem, it may send this message.

2.If the packet needs to be fragmented and the “don’t fragment” flag is set the host/router will send this message.

3.The source may have an incorrectly configured subnet mask.

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Recommended Action(s):

1.Check the routing tables of the router that this message was generated from.

2.Check the netmask configuration of the source.

3.Ignore this message if the D/F is meant to be set (no action required).

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