Bridging Packet Flow

Packets received over a Layer 2 logical interface for bridging when a normalized VLAN is configured with either the vlan-id or vlan-tags statements under the bridge domain or the VPLS routing instance are processed with the following steps:

1. A packet received on a physical port is only accepted for further processing if the VLAN tags of the received packet match the VLAN tags associated with one of the logical interfaces configured on that physical port.
2. The VLAN tags of the received packet are compared with the normalized VLAN tags. If the VLAN tags of the received packet are different from the normalized VLAN, then the appropriate VLAN operations (such as push-push, pop-pop, pop-swap, swap-swap, swap, and others) are done implicitly to convert the received VLAN tags to the normalized VLAN tag value. For more information these operations, see the JUNOS Routing Protocols Configuration Guide.
3. If the source MAC address of the received packet is not present in the source MAC table, then it is learned based on the normalized VLAN tag value.
4. The packet is forwarded toward one or more egress Layer 2 logical interfaces based on the destination MAC address. A packet with a known unicast destination MAC address is only forwarded to one egress logical interface. For each egress Layer 2 logical interface, the normalized VLAN tag within the packet is compared with the VLAN tags configured on that logical interface. If the VLAN tags associated with an egress logical interface do not match the normalized VLAN tag in the frame, then appropriate VLAN operations (such as push-push, pop-pop, pop-swap, swap-swap, swap, and others) are implicitly done to convert the normalized VLAN tags to the VLAN tags of the egress logical interface. For more information these operations, see the JUNOS Routing Protocols Configuration Guide.

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