VLANs with overlapping IP addresses

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Test isolation between VLANs with duplicate IPs.

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First: Static IP Addressing in a Single Subnet

Network

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PC1 and PC3 belong to VLAN 10; PC2 and PC4 belong to VLAN 20; SW1 p7 connects to SW2 p7 as an 802.1Q trunk.
VLAN 10: PC1 ↔ PC3. VLAN 20: PC2 ↔ PC4.
Open a console

1. Capture receiver traffic

The VLANs and trunk are configured. Each network uses .1 for its sender and .2 for its receiver.

PC3 and PC4

timeout 120 tcpdump -U --immediate-mode -i eth0 -w /tmp/lab-vlan.pcap "arp or icmp" &
capture_pid=$!
sleep 1

2. Send packets

PC1, then PC2

ping -n -c 3 -W 1 10.0.0.2

3. Verify isolation

PC3 and PC4

sleep 2
kill -INT "$capture_pid"
wait "$capture_pid" || true
tcpdump -nn -e -r /tmp/lab-vlan.pcap

Both pings should succeed. PC3 receives ICMP requests from MAC 02:00:00:00:00:01; PC4 receives them from 02:00:00:00:00:02. Neither capture should contain the other sender.

Validation

Click "Check". Once all steps pass, click "End".