ETHTap.sh

#!/bin/bash
set -xe

TAP_A=eth0
TAP_B=eth1

# Remove any IP addresses that may be set on the interfaces
ip address flush dev "$TAP_A"
ip address flush dev "$TAP_B"

# Clear (delete) any existing ingress qdiscs to avoid duplicates
tc qdisc del dev "$TAP_A" ingress 2>/dev/null || true
tc qdisc del dev "$TAP_B" ingress 2>/dev/null || true

# Add ingress qdiscs to both interfaces
tc qdisc add dev "$TAP_A" ingress
tc qdisc add dev "$TAP_B" ingress

# Mirror traffic from TAP_A to TAP_B
tc filter add \
  dev "$TAP_A" \
  parent ffff: \
  protocol all \
  u32 match u8 0 0 \
  action mirred egress mirror dev "$TAP_B"

# Mirror traffic from TAP_B to TAP_A
tc filter add \
  dev "$TAP_B" \
  parent ffff: \
  protocol all \
  u32 match u8 0 0 \
  action mirred egress mirror dev "$TAP_A"

# Disable IPv6 (this helps prevent IPv6 autoconfiguration packets)
sysctl -w net.ipv6.conf."$TAP_A".disable_ipv6=1
sysctl -w net.ipv6.conf."$TAP_B".disable_ipv6=1

# Bring up the interfaces and enable promiscuous mode
ip link set dev "$TAP_A" up promisc on
ip link set dev "$TAP_B" up promisc on