i've noticed two things rather recently.

1) microsoft's tracert program uses icmp echo requests (with varying
ttls) instead of udp packets to high numbered ports to accomplish the
same task.

2) the rfc (792) for icmp states that no icmp messages should be sent
about icmp messages.

is there an addendum to rfc792 that alters this restriction?  or is
microsoft merely lucky that it works and everyone is being a little
more permissive with what they send?

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