[PATCH 2/6] net: Add CONFIG_LEGACY_IP option

David Woodhouse
2026-04-01T07:45:44Z

From: David Woodhouse <dwmw@amazon.co.uk>

Add a new CONFIG_LEGACY_IP boolean option under CONFIG_INET that will
gate Legacy IP functionality. When disabled, the kernel will not
register the AF_INET socket family, IPv4 packet handler, ARP, or IPv4
routing, while the shared TCP/UDP/INET socket infrastructure remains
available for IPv6.

This is the first step toward making Legacy IP optional. The option
defaults to y and currently has no effect — subsequent patches will use
it to guard IPv4 entry points.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
net/ipv4/Kconfig | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index df922f9f5289..aef2c5349e62 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -2,6 +2,17 @@
#
# IP configuration
#
+config LEGACY_IP
+ bool "The IPv4 protocol (Legacy IP)"
+ help
+ Support for IP version 4 (IPv4).
+
+ Legacy IP is the protocol used by the early ARPANET, before IPv6
+ was standardised in the final decade of the 1900s. It should only
+ be necessary these days to interoperate with legacy networks.
+
+ If unsure, say N.
+
config IP_MULTICAST
bool "IP: multicasting"
help
--
2.51.0