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ICMP Normalizations

# ICMP Type Normalization Performed
1 Echo request Drop if destination is a multicast or broadcast address.
2 Echo request Optionally drop if ping checksum incorrect.
3 Echo request Zero ``code'' field.
4 Echo reply Optionally drop if ping checksum incorrect.
5 Echo reply Drop if no matching request.$\dagger$
6 Echo reply Zero ``code'' field.
7 Source quench Optionally drop to prevent DoS.$\dagger$
8 Destination Unreachable Unscramble embedded scrambled IP identifier.$\dagger$
9 other Drop.$\dagger$

The following ``transport'' protocols are recognized, but currently passed through unnormalized: IGMP, IP-in-IP, RSVP, IGRP, PGM.

Vern Paxson