Check if iproute2 is installed.
dpkg -s iproute2
Create a bridge interface.
ip link add name bridge0 type bridge
Add interfaces to the brigde.
ip link set eth0 master bridge0
ip link set eth1 master bridge0
Show interfaces added to the bridge.
bridge link show
Add an IP address to the bridge interface.
ip addr add 192.168.1.254/24 dev bridge0
Add a default gateway.
ip route add default via 192.168.1.1 dev bridge0
Check if tcpdump is installed.
dpkg -s tcpdump
Monitoring traffic.
tcpdump -i bridge0 -nn "icmp"