Am 06.11.2015 um 16:43 schrieb Johannes Ernst:
On Nov 6, 2015, at 1:09, Reindl Harald <[email protected]
<mailto:[email protected]>> wrote:

defaults should have security in mind, …

IMHO the current behavior is actually less secure:

no, it maybe unpredictable by the desciptions below but for sure not less secure

If I set net.ipv4.ip_forward=1, I intentionally set forwarding on all
interfaces, as documented in countless tutorials, so it’s very unlikely
I didn’t mean to do that.

depends on the number of networks

NIC1: wan
NIC2: lan with forwarding / nat
NIC3: SIP phones

NIC3 shouldn't forward because SIP phones connected to a asterisk tyoically don#t need to touch the internet directly in no direction

But if I set net.ipv4.ip_forward=1 in /etc/sysctl.d, and it only works
sometimes and on some interfaces, I do have a security problem because
it may come on when I least expect it. For example, when I execute
systemctl restart systemd-sysctl.

(Because networkd doesn’t actually “manage” the interface, it only sets
certain attributes at certain times, which can still be changed outside
of networkd any time. If net.ipv4.ip_forward were turned into a
read-only setting, for example, that would be different.)

well, because the sysctl stuff was unpredictable years ago i solved that by simply call "sysctl -p" after the network is up and never touch "systemd-sysctl"

[root@srv-rhsoft:~]$ cat /etc/systemd/system/sysctl-post-network.service
[Unit]
Description=apply settings after network
After=network.service systemd-networkd.service network-online.target openvpn.service hostapd.service network-wlan-bridge.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/sbin/sysctl -p
ExecStartPost=/usr/sbin/ifconfig wan -multicast -allmulti txqueuelen 100
StandardOutput=null

[Install]
WantedBy=multi-user.target

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