ICMP (4)
Linux IPv4 ICMP kernel module.
DESCRIPTION
This kernel protocol module implements the Internet Control Message Protocol
defined in RFC792. It is used to signal error conditions and for diagnosis.
The user doesn't interact directly with this module; instead it communicates
with the other protocols in the kernel and these pass the ICMP
errors to the application layers. The kernel ICMP module also
answers to ICMP requests.
A user protocol may receive ICMP packets for all local sockets by opening
a RAW socket with the protocol
IPPROTO_ICMP.
See
raw (4)
for more information.
The types of ICMP packets passed to the socket can be filtered using the
ICMP_FILTER
socket option. ICMP packets are always processed by the kernel too, even
when passed to a user socket.
Linux rate limits ICMP error packets per destination. ICMP_REDIRECT and
ICMP_DEST_UNREACH are limited per destination route of the incoming
packets.
SYSCTLS
ICMP supports a sysctl interface to configure some global IP parameters. The sysctls
can be accessed by reading or writing the
/proc/sys/net/ipv4/*
files or with the
sysctl (2)
interface. Most of these sysctls are rate limitations for specific ICMP types.
Linux 2.2 uses a token bucket filter to limit ICMPs.
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