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•Host Requirements RFC-1122 Section 3.2.2.6 states “An ICMP Echo
Request destined
to an IP broadcast or IP multicast address MAY be silently discarded.”
•IBM has provided a setting
in AIX 4.x to disable responses to broadcast addresses.
It is not available in AIX 3.x.
Use the "no" command to turn it off or on. NOTE: On AIX 4.x responses are DISABLED by
default.
•no -o bcastping=0 # disable bcast ping responses
(default)
•Solaris can be set not to
respond to broadcast ICMP echo requests.
Add the following line to your /etc/rc2.d/S69inet startup:
•ndd -set /dev/ip
ip_respond_to_echo_broadcast 0
•Starting with version
2.2.5, FreeBSD's IP stack does not respond to icmp echo requests destined to
broadcast and multicast addresses by default.
The sysctl parameter for this functionality is net.inet.icmp.bmcastecho.
•Under NetBSD, directed
broadcasts can be disabled by using the sysctl command:
•sysctl -w
net.inet.ip.directed-broadcast=0
•Under Linux, one can use
the CONFIG_IP_IGNORE_ECHO_REQUESTS variable to completely ignore ICMP echo requests. Of course, this violates RFC 1122.
•Any system (including
Linux) with ipfw can be protected by adding rules such as:
•ipfwadm -I -a deny -P icmp
-D 123.123.123.0 -S 0/0 0 8
•ipfwadm -I -a deny -P icmp
-D 123.123.123.255 -S 0/0 0 8
•(replace 123.123.123.0 and
123.123.123.255 with your base network number and broadcast address,
respectively)