Destination Unreachable (see Section 126.96.36.199)
Redirect (see Section 188.8.131.52)
Source Quench (see Section 184.108.40.206)
Time Exceeded (see Section 220.127.116.11)
Parameter Problem (see Section 18.104.22.168)
ICMP query messages:
Echo (see Section 22.214.171.124)
Information (see Section 126.96.36.199)
Timestamp (see Section 188.8.131.52)
Address Mask (see Section 184.108.40.206)
If an ICMP message of unknown type is received, it MUST be
Every ICMP error message includes the Internet header and at
least the first 8 data octets of the datagram that triggered
the error; more than 8 octets MAY be sent; this header and data
MUST be unchanged from the received datagram.
In those cases where the Internet layer is required to pass an
ICMP error message to the transport layer, the IP protocol
number MUST be extracted from the original header and used to
select the appropriate transport protocol entity to handle the
An ICMP error message SHOULD be sent with normal (i.e., zero)
An ICMP error message MUST NOT be sent as the result of
an ICMP error message, or
a datagram destined to an IP broadcast or IP multicast
a datagram sent as a link-layer broadcast, or
a non-initial fragment, or
a datagram whose source address does not define a single
host -- e.g., a zero address, a loopback address, a
broadcast address, a multicast address, or a Class E
NOTE: THESE RESTRICTIONS TAKE PRECEDENCE OVER ANY REQUIREMENT
ELSEWHERE IN THIS DOCUMENT FOR SENDING ICMP ERROR MESSAGES.
These rules will prevent the "broadcast storms" that have
resulted from hosts returning ICMP error messages in
response to broadcast datagrams. For example, a broadcast
UDP segment to a non-existent port could trigger a flood
of ICMP Destination Unreachable datagrams from all
machines that do not have a client for that destination
port. On a large Ethernet, the resulting collisions can
render the network useless for a second or more.
Every datagram that is broadcast on the connected network
should have a valid IP broadcast address as its IP
destination (see Section 3.3.6). However, some hosts
violate this rule. To be certain to detect broadcast
datagrams, therefore, hosts are required to check for a
link-layer broadcast as well as an IP-layer broadcast
This requires that the link layer inform the IP layer when
a link-layer broadcast datagram has been received; see
Protect yourself from cyberstalkers, identity thieves, and those who would snoop on you.
Stop spam from invading your inbox without losing the mail you want. We give you more control over your e-mail than any other service.
Block popups, ads, and malicious scripts while you surf the net through our anonymous proxies.
Participate in Usenet, host your web files, easily send anonymous messages, and more, much more.
All private, all encrypted, all secure, all in an easy to use service, and all for only $5.95 a month!