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This is a screenshot from a Cisco book. It says that 2 VLANs can be bridged using some L2 device also. As far as I know it is possible only by using some L3 device. Can someone please explain it how 2 VLANs can be bridged using a L2 device? enter image description here

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    You can short circuit two VLANs by using two layer 2 switches which individually connected ports are in the two respective VLANs. For instance, connect switch 1 port 1 in access VLAN 2 with switch 2 port 1 in access VLAN 3. Then traffic can flow from VLAN 2 to VLAN 3 and vice versa. You would need a bit more configuration though as the switch will probably shut down the port, when it receives a BPDU packet. Also the IP subnets might be different etc. – user36472 Jan 23 at 10:34
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A bridge / L2 device forwards frames based on the destination MAC address. Most often this is a common switch. If you bridge two VLANs they become a single L2 broadcast domain. Normally you wouldn't want that.

A router / L3 device forwards packets based on the destination IP address. If you use it to connect two VLANs they can communicate across the router (on L3/IP) but stay separate L2 broadcast domains.

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Simply put, if you bridge two VLANs together, they effectively become one VLAN.

There will no longer be a distinction between the VLANs -- they will act as one. For example a broadcast will be forwarded to all ports on both VLANs. Flooding will span both VLANs

  • So if I connect 2 vlans of the same switch using a cable, I would be able to send packets between 2 VLANs? – MUSR Jan 23 at 13:22
  • Yes (ignoring spanning tree). There will no longer be a distinction between the VLANs -- they will act as one. For example a broadcast will be forwarded to all ports on both VLANs. Flooding will span both VLANs. – Ron Trunk Jan 23 at 14:25

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