Filter mirrored port traffic using iptables

Your kernel ignores packages that are not addressed to the local network interfaces. You should change eth0 to promiscuous mode:

ip link set dev eth0 promisc on

You could make this persistent via the network configuration:

Debian

auto eth0
iface eth0 inet manual
    up ifconfig eth0 promisc up
    down ifconfig eth0 promisc down

Redhat

BOOTPROTO=static
DEVICE=eth0
TYPE=Ethernet
PROMISC=yes
...

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