A fusion device can be either a true routing platform, a Layer 3 switching platform, or a firewall must meet several technological requirements. It must support:
● Multiple VRFs—Multiple VRFs are needed for theVRF-Aware peermodel. For each VN that is handed off on the border node, a corresponding VN and interface is configured on the peer device. The selected platform should support the number of VNs used in the fabric site that will require access to shared services.
● Subinterfaces (Routers or Firewall)—A virtual Layer 3 interface that is associated with a VLAN ID on a routed physical interface. It extends IP routing capabilities to support VLAN configurations using the IEEE 802.1Q encapsulation.
● Switched Virtual Interfaces (Layer 3 switch)—Represents a logical Layer 3 interface on a switch. This SVI is a Layer 3 interface forwarding for a Layer 3 IEEE 802.1Q VLAN.
IEEE 802.1Q—An internal tagging mechanism which inserts a 4-byte tag field in the original Ethernet frame between the Source Address and Type/Length fields. Devices that support SVIs and subinterfaces will also support 802.1Q tagging
I don't understand why it needs to support vlan tagging. Is it because some of the packets it receives could be already tagged? That is my best guess. Other than that the fusion device is essentially providing VRF mapping at layer 3, so I can't understand why it require support for layer 2 tagging.
Hello On a L3 switch, Traffic that is associated to specific subnet/vlan is routed through a logical sub interface call a switched virtual interface (L3 SVI) However routers dont support SVIs only routed physical ports but they can be sub-divided into logical sub-interfaces These sub-interfaces can be also associated to a specific of subnet/vlan which is done by encapsulating traffic into a dot1q tag.
Best to just think of a tagged sub interface as a SVI residing on a router
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