When adding an IPv4 address, kernel automatically adds a local route. This is done by fib_add_ifaddr(). Note that if the address is IFA_F_SECONDARY, then the "src" is the primary address. That means, with
nmcli connection add con-name t type ethernet ifname t autoconnect no \
ipv4.method manual ipv6.method disabled \
ipv4.addresses '192.168.77.10/24, 192.168.77.11/24'we get two addresses:
"local 192.168.77.10 dev t table local proto kernel scope host src 192.168.77.10"
"local 192.168.77.11 dev t table local proto kernel scope host src 192.168.77.10"Our code would only generate instead:
"local 192.168.77.10 dev t table local proto kernel scope host src 192.168.77.10"
"local 192.168.77.11 dev t table local proto kernel scope host src 192.168.77.11"Afterwards, this artificial route can be leaked:
#!/bin/bash
set -vx
nmcli connection delete t || :
ip link delete t || :
ip link add name t type veth peer t-veth
nmcli connection add con-name t type ethernet ifname t autoconnect no ipv4.method manual ipv4.addresses '192.168.77.10/24, 192.168.77.11/24' ipv6.method disabled
nmcli connection up t
ip route show table all dev t | grep --color '^\|192.168.77.11'
sleep 1
nmcli device modify t -ipv4.addresses 192.168.77.11/24
ip route show table all dev t | grep --color '^\|192.168.77.11'
ip route show table all dev t | grep -q 192.168.77.11 && echo "the local route 192.168.77.11 is still there, because NM adds a local route with wrong pref-src"This was introduced by commit 3e5fc04d ('core: add dependent local routes configured by kernel'), but it's unclear to me why we really need this. Drop it again and effectively revert 3e5fc04d.