...
Assigning devices to namespaces
ip link set tap<tap_red red> netns ns<ns_redred>
ip link set tap<tap_blue blue> netns ns_blue<ns_blue>
ip link set eth1 netns ns1
Setting the same IP address
ip netns exec ns_red ip ad add 10.200.1.2/24 dev tap_red
ip netns exec ns_blue ip ad add 10.200.1.2/24 dev tap_blue
ip netns exec ns_red ip li set tap_red up
ip netns exec ns_blue ip li set tap_blue up
...