Scenario routing and Switching

 

• You have three routers (R1, R2, R3) connected with serial links, running routing.

• You have three switches (SW1, SW2, SW3) connected with EtherChannel (LACP).

• PCs A, B, C are connected to switches with VLAN 1 IP addresses.

• VLAN interfaces (SVI) are configured on the switches with IPs in the 172.16.x.x ranges.

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Your Question: “Can I add one interface into 2 VLANs?”

Looking at your design:

• Ports like F0/6 (PC-A), F0/18 (PC-B), F0/18 (PC-C) are access ports.
  👉 These cannot belong to two VLANs at once. Each port is tied to only one VLAN.

• Your switch interconnects (F0/1, F0/2, F0/3, F0/4) are bundled in an EtherChannel (trunk).
  👉 Here, you can allow multiple VLANs to pass through (e.g., VLAN 10, VLAN 20), but the frames are tagged so each belongs to a single VLAN at a time.

• If you want PC-A in VLAN 10 and VLAN 20, that’s not possible with one NIC.
  But if the PC had a second NIC (or supported VLAN tagging in its OS), then you could connect it to both VLANs via trunk mode.

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✅ Key Rule:

• Access port → 1 VLAN only.

• Trunk/EtherChannel port → multiple VLANs (tagged traffic).

• Voice + Data VLAN → exception, 1 port can carry 2 VLANs (one for voice, one for data).