Fabric Attach is typically deployed in the access layer(s) of a Fabric Connect network.
Fabric Attach, when used with a Fabric Connect solution, provides the same capabilities at the access layer, but those services and policies are mapped across the entire network end-to-end. FA makes user and end device attachment simple and creates network configuration and sets up resources only when needed.
An FA Server can be connected to FA Client or FA Proxy devices on three types of interfaces, namely, a port, MLT or an SMLT. The following sections discuss FA in SMLT and non-SMLT deployments.
The following deployment shows an SPBM network in which one edge has manually configured Switched UNI I-SIDs and the other edge has Fabric Attach (FA). At the FA edge, the I-SIDs are learned using FA TLVs and are automatically created on the FA Server as ELAN I-SIDs with Switched UNI endpoints.
This deployment demonstrates that the FA-created I-SIDs can communicate with any other I-SID (manually created Switched UNI or a C-VLAN with an I-SID), on the local switch or across the SPBM fabric, as long as the I-SID values are the same.
BEB-B is a switch acting as the FA Server with a network-to-network interface (NNI) to the SPBM cloud. FA Client and FA Proxy devices send I-SID-to-VLAN mapping requests to the FA Server on the respective FA-enabled ports, using LLDP TLVs. This enables the I-SID endpoints to communicate with the SPB cloud.
If several clients are aggregated in an MLT, at least one of the ports must send the mapping requests for the FA Server to create the I-SID endpoints for that MLT. For example, let Client 2 be a wireless FA Client (such as an WLAN 9100 AP device) on port 1/21, that sends an FA mapping request for I-SID 100 and C-VID (VLAN ID) 100. The FA Server (BEB-B) creates the requested I-SID 100 on its device, and advertises it to the SPB cloud.
BEB-A has manually configured Switched UNI endpoints, one of which is Client 1 (connected at port 1/1) using the same I-SID value 100.
With this setup, data traffic can freely flow between Client 1 and Client 2 through the two BEBs and the BCB.
Thus the Switched UNI I-SIDs learned using FA TLVs on one edge of the Fabric Connect (SPBM) network can communicate with the manually created I-SIDs on the other edge, as long as they both have the same value.
The following examples discuss FA in dual-homed and single-homed SMLT deployments.
Fabric Attach in a dual-homed SMLT deployment
The following section describes FA in a dual-homed SMLT deployment. A pair of switches that operate as IST peers act as the FA Server. An FA Proxy (typically a wiring closet switch or an access switch) is connected to FA Clients and in turn to end devices. The FA Clients or FA Proxies advertise I-SID-to-VLAN mappings namely the interface C-VID and the I-SID to the FA Server switches. Both switches receive the mapping information using LLDP TLVs. The switch that learns the mapping first from the LLDP TLV considers the I-SID endpoint to be discovered locally, and creates the I-SID on its device. It then sends the mapping information to its peer switch. When the peer switch receives the mapping across IST in a new SMLT message, it too creates the I-SID and endpoint on its device. This I-SID however, is considered to be discovered remotely, because the data was synchronized from its peer.
Note
For the peer switches acting as the FA Server to transmit the same FA System ID (based on the virtual MAC), SMLT configuration must be the same on both peers.
For successful FA operation, configuration of FA message authentication and the authentication key must be the same on both peers.
For successful operation in Layer 3, a platform VLAN must be configured on both peers. This is necessary for proper MAC learning.
In the above example deployment, BEB-A and BEB-B are IST peers collectively acting as the FA Server. FA TLVs sent from the clients (through the proxy) are learned on FA-enabled ports on BEB-A and BEB-B. When BEB-A learns the mapping for the first time on its port, it creates an I-SID on its device. This is considered locally discovered. In addition, it sends an SMLT message to its peer BEB-B, which also creates the I-SID on its device. This time, the I-SID is considered remotely discovered. Similarly, if BEB-B receives a mapping from a client for the first time, it creates an I-SID (locally discovered) and also sends an IST message to its peer to create an I-SID (remotely discovered).
Irrespective of whether the I-SID creation on the FA peers is triggered by a local TLV event or by messaging from the IST peer, they can both receive data traffic. Thus in a dual-homed SMLT deployment, any I-SID can be learned irrespective of whether it is discovered locally, discovered remotely or both.
Note
On the IST peers, if an FA TLV is learned on a port or normal MLT (instead of the admin SMLT), only the I-SID is sent to the peer switch.
Fabric Attach in a single-homed SMLT deployment
In the single-homed SMLT, as shown in the following deployment, the FA Server creates either a locally discovered I-SID (if received from a client using FA TLVs) or a remotely discovered I-SID (if synchronized from its IST peer), but not both.
