After you enable FabricPath on the switches that you are using, you can configure an Ethernet interface or a port-channel interface as a FabricPath interface. If one member of the port channel is in FabricPath mode, all the other members will be in FabricPath mode. After you configure the interface as a FabricPath interface, it automatically becomes a trunk port, capable of carrying traffic for multiple VLANs. You can also configure all the ports on the switch as FabricPath interfaces simultaneously.
The following interface modes carry traffic for the following types of VLANs:
- Interfaces on the switch that are configured as FabricPath interfaces can carry traffic only for FabricPath VLANs.
- Interfaces on the switch that are not configured as FabricPath interfaces carry traffic for the following:
– FabricPath VLANs
– Classical Ethernet (CE) VLANS
See “Configuring FabricPath Forwarding,” for information about FabricPath and CE VLANs.
The FabricPath interfaces connect only to other FabricPath interfaces within the FabricPath network. These FabricPath ports operate on the information in the FabricPath headers and Layer 2 Intermediate System-to-Intermediate System (IS-IS) only, and they do not run STP. These ports are aware only of FabricPath VLANs; they are unaware of any CE VLANs. By default, all VLANs are allowed on a trunk port, so the FabricPath interface carries traffic for all FabricPath VLANs.
STP and the FabricPath Network
The Layer 2 gateway switches, which are on the edge between the CE and the FabricPath network, must be configured as the root for all Spanning Tree Protocol (STP) domains that are connected to a FabricPath network.
The STP domains do not cross into the FabricPath network (see Figure 3-1).
Figure 3-1 STP Boundary Termination at FabricPath Network Border
You must configure the FabricPath Layer 2 gateway switch to have the lowest STP priority of all the switches in the STP domain to which it is attached. You must also configure all the FabricPath Layer 2 gateway switches that are connected to one FabricPath network to have the same priority. The software assigns the bridge ID for the Layer 2 gateway switches from a pool of reserved MAC addresses.
To ensure a loop-free topology for the CE/FabricPath hybrid network, the FabricPath network automatically displays as a single bridge to all connected CE switches.
Note You must set the STP priority on all FabricPath Layer 2 gateway switches to a value low enough to ensure that they become root for any attached STP domains.
Other than configuring the STP priority on the FabricPath Layer 2 gateway switches, you do not need to configure anything for the STP to work seamlessly with the FabricPath network. Only connected CE switches form a single STP domain. Those CE switches that are not interconnected form separate STP domains (see Figure 3-1).
All CE interfaces should be designated ports, which occurs automatically, or they are pruned from the active STP topology. If the software prunes any port, the software returns a syslog message. The software clears the port again only when that port is no longer receiving superior BPDUs.
The FabricPath Layer 2 gateway switch also propagates the Topology Change Notifications (TCNs) on all its CE interfaces.
The FabricPath Layer 2 gateway switches terminate STP. The set of FabricPath Layer 2 gateway switches that are connected by STP forms the STP domain. Because many FabricPath Layer 2 gateway switches might be attached to a single FabricPath network, there might also be many separate STP domains (see Figure 3-1). The switches in the separate STP domains need to know the TCN information only for the domain to which they belong. You can configure a unique STP domain ID for each separate STP domain that connects to the same FabricPath network. The Layer 2 IS-IS messages carry the TCNs across the FabricPath network. Only those FabricPath Layer 2 gateway switches in the same STP domain as the TCN message need to act and propagate the message to connected CE switches.
When a FabricPath Layer 2 gateway switch receives a TCN for the STP domain it is part of, it takes the following actions:
- Flushes all remote MAC addresses for that STP domain and the MAC addresses on the designated port.
- Propagates the TCN to the other switches in the specified STP domain.
The switches in the separate STP domains need to receive the TCN information and then flush all remote MAC addresses reachable by the STP domain that generated the TCN information.
A virtual port channel+ (vPC+) domain allows a classical Ethernet (CE) vPC domain and a Cisco FabricPath cloud to interoperate. A vPC+ also provides a First Hop Routing Protocol (FHRP) active-active capability at the FabricPath to Layer 3 boundary.
Note vPC+ is an extension to virtual port channels (vPCs) that run CE only.. You cannot configure a vPC+ domain and a vPC domain on the same Cisco Nexus device.
A vPC+ domain enables a Cisco Nexus device that has FabricPath enabled to form a single vPC+, which is a unique virtual switch to the rest of the FabricPath network. You configure the same domain on each switch to enable the peers to identify each other and to form the vPC+. Each vPC+ has its own virtual switch ID.
Note We do not recommend that you enable the vPC peer switch feature when you are using a vPC+.
A vPC+ must still provide active-active Layer 2 paths for dual-homed CE switches or clouds, even though the FabricPath network allows only 1-to-1 mapping between the MAC address and the switch ID. vPC+ provides the solution by creating a unique virtual switch to the FabricPath network (see Figure 3-2).
Figure 3-2 Comparison of vPC and vPC+
The FabricPath switch ID for the virtual switch becomes the outer source MAC address (OSA) in the FabricPath encapsulation header. Each vPC+ domain must have its own virtual switch ID.
Layer 2 multipathing is achieved by emulating a single virtual switch. Packets forwarded from host A to host B are sent to the MAC address of the virtual switch as the transit source, and traffic from host B to host A is now load balanced.
The vPC+ downstream links are FabricPath edge interfaces that connect to the CE hosts.
The First Hop Routing Protocols (FHRPs), which include the Hot Standby Routing Protocol (HSRP) and the Virtual Router Redundancy Protocol (VRRP), interoperate with a vPC+. You should dual-attach all Layer 3 switches to both vPC+ peer switches.
Note You must enable the Layer 3 connectivity from each vPC+ peer switch by configuring a VLAN network interface for the same VLAN from both switches.
Both the primary and secondary vPC+ switches forward traffic, but only the primary FHRP switch responds to ARP requests.
To simplify initial configuration verification and vPC+/HSRP troubleshooting, you can configure the primary vPC+ peer switch with the FHRP active router highest priority.
In addition, you can use the priority command in the if-hsrp configuration mode to configure failover thresholds for when a group state enabled on a vPC+ peer is in standby or in listen state. You can configure lower and upper thresholds to prevent the group state flap, if there is an interface flap (this feature is useful when there is more than one tracking object per group).
When the primary vPC+ peer switch fails over to the secondary vPC+ peer switch, the FHRP traffic continues to flow seamlessly.
You should configure a separate Layer 3 link for routing from the vPC+ peer switches, rather than using a VLAN network interface for this purpose.
We do not recommend that you configure the burnt-in MAC address option (use-bia) for hot standby router protocol HSRP or manually configure virtual MAC addresses for any FHRP protocol in a vPC+ environment because these configurations can adversely affect the vPC+ load balancing.
The HSRP use-bia is not supported with a vPC+. When you are configuring custom MAC addresses, you must configure the same MAC address on both vPC+ peer switches.
You can configure a restore timer that delays the vPC+ coming back up until after the peer adjacency forms and the VLAN interfaces are back up. This feature allows you to avoid packet drops if the routing tables do not converge before the vPC+ is once again passing traffic.
Use the delay restore command to configure this feature.
See the Cisco Nexus 6000 Series NX-OS Unicast Routing Configuration Guide, Release 6.0 for more information on FHRPs and routing.