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generic: 5.10: backport Treat IPv4 segment's lowest address as unicast

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Backport patch from kernel 5.14.

Treat only the highest, not the lowest, IPv4 address within a local
subnet as a broadcast address, as subnets do not need two different
broadcast addresses and networking documentation consistently prefers
the highest address as broadcast.

This patch was merged in upstream net-next tree in May 2021 at

https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=94c821c74bf5

This eventually frees up one address per subnet. It matches behavior
suggested in our Internet-Draft, and also the default behavior of OpenBSD
and FreeBSD.

Signed-off-by: Seth David Schoen <schoen@loyalty.org>
This commit is contained in:
Seth David Schoen 2023-01-02 20:42:50 -08:00 committed by Hauke Mehrtens
parent 738b04c881
commit 68f983ba41
1 changed files with 32 additions and 0 deletions
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32
target/linux/generic/backport-5.10/615-v5.14-ip-Treat-IPv4-segment-s-lowest-address-as-unicast.patch Normal file
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@ -0,0 +1,32 @@
From 94c821c74bf5fe0c25e09df5334a16f98608db90 Mon Sep 17 00:00:00 2001
From: Seth David Schoen <schoen@loyalty.org>
Date: Wed, 12 May 2021 21:37:49 -0700
Subject: [PATCH] ip: Treat IPv4 segment's lowest address as unicast
Treat only the highest, not the lowest, IPv4 address within a local
subnet as a broadcast address.
Signed-off-by: Seth David Schoen <schoen@loyalty.org>
Suggested-by: John Gilmore <gnu@toad.com>
Acked-by: Dave Taht <dave.taht@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=94c821c74bf5
---
net/ipv4/fib_frontend.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1129,10 +1129,8 @@ void fib_add_ifaddr(struct in_ifaddr *if
prefix, ifa->ifa_prefixlen, prim,
ifa->ifa_rt_priority);
- /* Add network specific broadcasts, when it takes a sense */
+ /* Add the network broadcast address, when it makes sense */
if (ifa->ifa_prefixlen < 31) {
- fib_magic(RTM_NEWROUTE, RTN_BROADCAST, prefix, 32,
- prim, 0);
fib_magic(RTM_NEWROUTE, RTN_BROADCAST, prefix | ~mask,
32, prim, 0);
arp_invalidate(dev, prefix | ~mask, false);