The Fabric Connect technology delivers Layer 2 and Layer 3 virtualization. These virtualized Layer 2 and Layer 3 instances are referred to as Virtual Service Networks (VSNs). A Service Identifier (I-SID) is used to uniquely distinguish these service instances network-wide, and a User Network Interface (UNI) is the boundary or demarcation point between the “service layer” of traditional networks, that is VLANs and VRFs, and the Fabric Connect “service layer”, that is Layer 2 & Layer 3 VSNs.
Layer 2 VSNs are virtual broadcast domains interconnecting UNI members that share the same Layer 2 VSN I-SID. MAC learning/aging is applied to all Layer 2 VSNs.
Layer 3 VSNs are virtual routed Layer 3 networks (Layer 3 VPN) leveraging IS-IS as the routing protocol between VRFs that share the same Layer 3 VSN I-SID.
Fabric Connect uses the User-Network-Interface (UNI) to denote the capabilities and attributes of the service interfaces. Fabric connect devices support the following UNI types:
VLAN UNI (C-VLAN) — a device-specific VLAN-ID maps to a Layer 2 VSN I-SID – all device physical ports that are associated with the VLAN are therefore associated with the UNI.
Flex UNI — it has the following sub-types:
Switched UNI — a VLAN-ID and a given port (VID, port) maps to a Layer 2 VSN I-SID. With this UNI type, VLAN-IDs can be reused on other ports and therefore mapped to different I-SIDs.
Transparent Port UNI — a physical port maps to a Layer 2 VSN I-SID (all traffic through that port, 802.1Q tagged or untagged, ingress and egress is mapped to the I-SID). Note: All VLANs on a Transparent Port UNI interface now share the same single MAC learning table of the Transparent Port UNI I-SID.
E-Tree UNI — it extends Private VLANs beyond one Switch to form a network-wide E-Tree service infrastructure. An E-Tree UNI is a Layer 2 VSN where broadcast traffic flows from Hub sites to Spokes sites, and from Spokes to Hubs, but not between Spoke sites. E-Tree Hubs can be formed with any VLAN UNI, while E-Tree Spokes must be configured as Private VLAN UNIs.
Layer 3 VSN UNI — a device-specific VRF maps to an I-SID, and the control plane exchanges the Layer 3 routes belonging to the same I-SID. All VRFs in a network sharing the same Layer 3 I-SID effectively form an Layer 3 VPN. Layer 3 VSNs can be configured to simultaneously support both IP Unicast and IP Multicast.