Host interfaces are for host or server connectivity only; host interfaces cannot connect to another network. These interfaces are always enabled as edge ports; as they come up, these ports immediately transition to the forwarding state. Host interfaces are always enabled with BPDU Guard. If a BPDU is received, the port is immediately placed in an error-disabled state which keeps the link down.

You can enable host interfaces to accept Cisco Discovery Protocol (CDP) packets. This protocol only works when it is enabled for both ends of a link.

Note	CDP is not supported on fabric interfaces when the Fabric Extender is configured in a virtual port channel (vPC) topology.

Ingress and egress packet counters are provided on each host interface.

For more information about BPDU Guard and CDP see the Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 4.2(1)N1(1).

The Cisco Nexus 2248TP and Cisco Nexus 2232PP support EtherChannel host interface configurations. Up to 8 interfaces can be combined in an EtherChannel. The EtherChannel can be configured with or without LACP.

Note	Support for host interface EtherChannel was added to the Fabric Extender from Cisco NX-OS Release 4.2(1)N1(1).

For more information about EtherChannels see the Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 4.2(1)N1(1).

The Fabric Extender supports Layer 2 VLAN trunks and IEEE 802.1Q VLAN encapsulation. Host interfaces can be members of private VLANs with the following restrictions:

• You can configure a host interface as an isolated or community access port only.

• You cannot configure a host interface as a promiscuous port.

• You cannot configure a host interface as a private VLAN trunk port.

For more information about promiscuous, community, and isolated ports in private VLANs see the Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 4.2(1)N1(1).

Using a virtual port channel (vPC) you can configure topologies where a Cisco Nexus 2000 Series Fabric Extender is connected to a pair of parent switches or a pair of Fabric Extenders are connected to a single parent switch. The vPC can provide multipath connections, which allow you to create redundancy between the nodes on your network.

The following vPC topologies are possible with the Fabric Extender:

• The parent switches are connected single homed to Fabric Extenders which are subsequently connected to servers with dual interfaces (see the following figure).

  Figure 2. Single Homed Fabric Extender vPC Topology
  
  

• The Fabric Extender is connected dual homed to two upstream parent switches and connected downstream to single homed servers (see the following figure).

  Figure 3. Dual Homed Fabric Extender vPC Topology
  
  

  This configuration is also called Active-Active topology.

See the Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 4.2(1)N1(1) for vPC configuration details.

The Cisco Nexus 2232PP supports Fibre Channel over Ethernet (FCoE) with the following restrictions:

• Only FCoE Initialization Protocol (FIP) enabled converged network adapters (CNAs) are supported on the Fabric Extender.

• Binding to an EtherChannel is limited to only one member EtherChannel.

See the Cisco Nexus 5000 Series NX-OS Fibre Channel over Ethernet Configuration Guide, Release 4.2(1)N1(1) for configuration details.

To reduce the load on the control plane of the Cisco Nexus 5000 Series device, Cisco NX-OS provides the ability to offload link-level protocol processing to the Fabric Extender CPU. The following protocols are supported:

• Link Layer Discovery Protocol (LLDP) and Data Center Bridging Exchange (DCBX)

• Cisco Discovery Protocol (CDP)

• Link Aggregation Control Protocol (LACP)

The Fabric Extender provides two user queues for its quality of service (QoS) support, one for all no-drop classes and one for all drop classes. The classes configured on its parent switch are mapped to one of these two queues; traffic for no-drop classes is mapped to one queue and traffic for all drop classes is mapped to the other. Egress policies are also restricted to these two classes.

The parent switch provides two predefined type qos class maps for matching broadcast or multicast traffic; class-all-flood and class-ip-multicast. These classes are ignored on the Fabric Extender.

The Fabric Extender uses IEEE 802.1p class of service (CoS) values to associate traffic with the appropriate class. Per-port QoS configuration and CoS-based egress queuing is also supported.

Host interfaces support pause frames, which is implemented using IEEE 802.3x link-level flow control (LLC). By default, flow control send is on and flow control receive is off on all host interfaces. Autonegotiation is enabled on the host interfaces. Per-class flow control is set according to the QoS classes.

Host interfaces support jumbo frames (up to 9216 bytes); however a per-host interface maximum transmission unit (MTU) is not supported. Instead, MTU is set according to the QoS classes. You modify MTU by setting policy and class maps on the parent switch. Because the Fabric Extender has only two user queues, the MTU for the drop-queue is set to the maximum MTU of all drop classes and the MTU on the no-drop queue is set to the maximum MTU of all no-drop classes.

For more information about LLC and quality of service, see the Cisco Nexus 5000 Series NX-OS Quality of Service Configuration Guide, Release 4.2(1)N1(1).

The Fabric Extender supports the full range of ingress access control lists (ACLs) that are available on its parent switch.

For more information about ACLs see the Cisco Nexus 5000 Series NX-OS Security Configuration Guide, Release 4.2(1)N1(1).

You can configure the host interfaces on the Fabric Extender as Switched Port Analyzer (SPAN) source ports. Fabric Extender ports cannot be configured as a SPAN destination. Only one SPAN session is supported for all the host interfaces on the same Fabric Extender. Ingress source (Rx), egress source (Tx), or both ingress and egress monitoring is supported.

Note

All IP multicast traffic on the set of VLANs that a Fabric Extender host interface belongs to is captured in the SPAN session. It is not possible to separate the traffic by IP multicast group membership. If ingress and egress monitoring is configured for host interfaces on the same Fabric Extender, you may see a packet twice: once as the packet ingresses on an interface with Rx configured, and again as the packet egresses on an interface with Tx configured.

For more information about SPAN see the Cisco Nexus 5000 Series NX-OS System Management Configuration Guide, Release 4.2(1)N1(1)

The Fabric Extender fabric interfaces support static EtherChannel and priority flow control (PFC). PFC allows you to apply pause functionality to specific classes of traffic on an interface (instead of all the traffic on the interface). During the initial discovery and association process, SFP+ validation and digital optical monitoring (DOM) are performed as follows:

• The Fabric Extender performs a local check on the uplink SFP+ transceiver. If it fails the security check, the LED flashes but the link is still allowed to come up.

• The Fabric Extender local check is bypassed if it is running its backup image.

• The parent switch performs SFP validation again when the fabric interface is brought up. It keeps the fabric interface down if SFP validation fails.

Once an interface on the parent switch is configured in fex-fabric mode, all other features that were configured on that port and are not relevant to this mode are deactivated. If the interface is reconfigured to remove fex-fabric mode, the previous configurations are reactivated.

Note	Per class flow control mode is enabled by default on the fabric interfaces. When a fabric interface is configured on the parent switch, PFC mode is enabled by default and cannot be changed.

For more information about PFC see the Cisco Nexus 5000 Series NX-OS Quality of Service Configuration Guide, Release 4.2(1)N1(1)

To provide a deterministic relationship between the host interfaces and the parent switch, you can configure the Fabric Extender to use individual fabric interface connections. This configuration connects the 10-Gigabit Ethernet fabric interfaces as shown in the following figure. You can use any number of fabric interfaces up to the maximum available on the model of the Fabric Extender.

Figure 5. Static Pinning Fabric Interface Connections

When the Fabric Extender is brought up, its host interfaces are distributed equally among the available fabric interfaces. As a result, the bandwidth that is dedicated to each end host toward the parent switch is never changed by the switch but instead is always specified by you.

Note	If a fabric interface fails, all its associated host interfaces are brought down and remain down until the fabric interface is restored.

You must use the pinning max-links command to create a number of pinned fabric interface connections so that the parent switch can determine a distribution of host interfaces. The host interfaces are divided by the number of the max-links and distributed accordingly. The default value is max-links 1.

Caution

Changing the value of the max-links is disruptive; all the host interfaces on the Fabric Extender are brought down and back up as the parent switch reassigns its static pinning.

The pinning order of the host interfaces is initially determined by the order in which the fabric interfaces were configured. When the parent switch is restarted, the configured fabric interfaces are pinned to the host interfaces in an ascending order by the port number of the fabric interface.

To guarantee a deterministic and sticky association across a reboot, you can manually redistribute the pinning.

Note	The redistribution of the host interfaces will always be in an ascending order by the port number of the fabric interface.

To provide load balancing between the host interfaces and the parent switch, you can configure the Fabric Extender to use an EtherChannel fabric interface connection. This connection bundles 10-Gigabit Ethernet fabric interfaces into a single logical channel as shown in the following figure.

Figure 6. EtherChannel Fabric Interface Connection

When you configure the Fabric Extender to use an EtherChannel fabric interface connection to its parent switch, the switch load balances the traffic from the hosts that are connected to the host interface ports by using the following load-balancing criteria to select the link:

• For a Layer 2 frame, the switch uses the source and destination MAC addresses.

• For a Layer 3 frame, the switch uses the source and destination MAC addresses and the source and destination IP addresses.

Note	A fabric interface that fails in the EtherChannel will not trigger a change to the host interfaces. Traffic is automatically redistributed across the remaining links in the EtherChannel fabric interface.

The Cisco Nexus 2000 Series Fabric Extender is a 1 RU chassis that is designed for rack mounting. The chassis supports redundant hot-swappable fans and power supplies.

There are three models of the Cisco Nexus 2000 Series Fabric Extender:

• The Cisco Nexus 2148T has 48 1000BASE-T Ethernet host interfaces for its downlink connection to servers or hosts and 4 10-Gigabit Ethernet fabric interfaces with SFP+ interface adapters for its uplink connection to the parent switch.

• The Cisco Nexus 2248TP has 48 100BASE-T/1000Base-T Ethernet host interfaces for its downlink connection to servers or hosts and 4 10-Gigabit Ethernet fabric interfaces with SFP+ interface adapters for its uplink connection to the parent switch.

• The Cisco Nexus 2232PP has 32 10-Gigabit Ethernet host interfaces with SFP+ interface adapters and 8 10-Gigabit Ethernet fabric interfaces with SFP+ interface adapters for its uplink connection to the parent switch.