Add a more detailed description of the IP addresses that have
a special meaning in Internet standards, and how these affect
Linux.
Signed-off-by: Seth David Schoen <schoen@xxxxxxxxxxx>
Suggested-by: John Gilmore <gnu@xxxxxxxx>
---
man7/ip.7 | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/man7/ip.7 b/man7/ip.7
index d9299eb9e..478cda269 100644
--- a/man7/ip.7
+++ b/man7/ip.7
@@ -39,7 +39,7 @@
.\" commit 76e21053b5bf33a07c76f99d27a74238310e3c71
.\" Author: Erich E. Hoover <ehoover@xxxxxxxxx>
.\"
-.TH IP 7 2020-11-01 "Linux" "Linux Programmer's Manual"
+.TH IP 7 2021-03-10 "Linux" "Linux Programmer's Manual"
.SH NAME
ip \- Linux IPv4 protocol implementation
.SH SYNOPSIS
@@ -232,6 +232,7 @@ In particular, this means that you need to call
on the number that is assigned to a port.
All address/port manipulation
functions in the standard library work in network byte order.
+.SS Special and reserved addresses
.PP
There are several special addresses:
.B INADDR_LOOPBACK
@@ -245,6 +246,25 @@ means any address for binding;
means any host and has the same effect on bind as
.B INADDR_ANY
for historical reasons.
+.PP
+Internet standards have also traditionally reserved various
+addresses for particular uses. The addresses
+in the ranges 0.0.0.0 through 0.255.255.255 and 240.0.0.0 through
+255.255.255.254 (0/8 and 240/4 in CIDR notation) are reserved globally
+(but Linux permits addresses within these ranges, other than 0.0.0.0,
+to be assigned to an interface and used like other unicast addresses).
+All addresses in 127.0.0.0 through 127.255.255.255
+("127/8") are treated as loopback addresses akin to the standardized
+local loopback address 127.0.0.1, while addresses in 224.0.0.0 through
+239.255.255.255 ("224/4") are dedicated to multicast use.
+.PP
+On any locally-attached IP subnet, the lowest-numbered address and
+highest-numbered address (e.g., the .0 and .255 addresses on a subnet
+with netmask 255.255.255.0) are both designated as broadcast addresses.
+These cannot usefully be assigned to an interface, and can only be
+addressed with a socket on which the
+.B SO_BROADCAST
+option has been explicitly enabled.
.SS Socket options
IP supports some protocol-specific socket options that can be set with
.BR setsockopt (2)
--
2.25.1
