rfc1122 (host requirements) says:
An ICMP error message MUST NOT be sent as the result of
receiving:
...
* a datagram destined to an IP broadcast or IP multicast
address, or
* a datagram sent as a link-layer broadcast, or
...
however, rfc2463 (icmpv6) weakens this:
(e) An ICMPv6 error message MUST NOT be sent as a result of
receiving:
...
(e.2) a packet destined to an IPv6 multicast address (there
are two exceptions to this rule: (1) the Packet Too Big
Message - Section 3.2 - to allow Path MTU discovery to
work for IPv6 multicast, and (2) the Parameter Problem
Message, Code 2 - Section 3.4 - reporting an
unrecognized IPv6 option that has the Option Type
highest-order two bits set to 10), or
(e.3) a packet sent as a link-layer multicast, (the exception
from e.2 applies to this case too), or
(e.4) a packet sent as a link-layer broadcast, (the exception
from e.2 applies to this case too), or
The path mtu discovery case almost makes sense, and topologies which
could be abused into being "smurf" amplifiers may well be very rare in
practice.
[I do it odd that there's no rationale given for responding with a
"parameter problem"..]
- Bill
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