Overview

This chapter provides an architectural overview of the Cisco Nexus 2000 Series Fabric Extender and includes the following sections:

Information About the Cisco Nexus 2000 Series Fabric Extender

The Cisco Nexus 2000 Series Fabric Extender, also known as FEX, is a highly scalable and flexible server networking solution that works with Cisco Nexus Series devices to provide high-density, low-cost connectivity for server aggregation. Scaling across 1-Gigabit Ethernet, 10-Gigabit Ethernet, unified fabric, rack, and blade server environments, the Fabric Extender is designed to simplify data center architecture and operations.

The Fabric Extender integrates with its parent switch, which is a Cisco Nexus Series device, to allow automatic provisioning and configuration taken from the settings on the parent device. This integration allows large numbers of servers and hosts to be supported by using the same feature set as the parent device with a single management domain. The Fabric Extender and its parent switch enable a large multipath, loop-free, active-active data center topology without the use of the Spanning Tree Protocol (STP).

The Cisco Nexus 2000 Series Fabric Extender forwards all traffic to its parent Cisco Nexus Series device over 10-Gigabit Ethernet fabric uplinks, which allows all traffic to be inspected by policies established on the Cisco Nexus Series device.

No software is included with the Fabric Extender. The software is automatically downloaded and upgraded from its parent device.


Note

When you configure a Cisco Nexus 2248 port to 100mbps speed (instead of auto-negotiation), FEX does not auto negotiate with the peer. You must manually set the peer not to auto negotiate and set the peer to 100mbps speed.

Fabric Extender Terminology

Some terms used in this document are as follows:

  • Fabric interface—A 10-Gigabit Ethernet uplink port that is designated for connection from the Fabric Extender to its parent switch. A fabric interface cannot be used for any other purpose. It must be directly connected to the parent switch.


    Note

    A fabric interface includes the corresponding interface on the parent switch. This interface is enabled when you enter the switchport mode fex-fabric command.

  • Port channel fabric interface—A port channel uplink connection from the Fabric Extender to its parent switch. This connection consists of fabric interfaces that are bundled into a single logical channel.

  • Host interface—An Ethernet host interface for connection to a server or host system.


    Note

    Do not connect a bridge or switch to a host interface. These interfaces are designed to provide end host or server connectivity.


    Note

    On Cisco Nexus 2348TQ and Nexus 2348UPQ FEX, if a port channel is used to connect a parent switch with a Fabric Extender device, the port channels can have maximum of 8 ports.

    The Nexus 2348 FEX devices have a total of 6 * 40 Gigabit Ethernet uplink ports towards the parent switch. If these are used with native 40G uplinks port on a parent switch, then there is no limitation. All 6 ports can be used in either single homed or dual homed configuration. You can also use 40 Gigabit Ethernet uplink ports on the N2348 Fabric Extender device with 10 Gigabit Ethernet ports on the parent switch when used with the appropriate cabling. A maximum of 8 ports can be added to the port channel between the parent switch and Fabric Extender device. If it is a dual homed setup, VPC to the Fabric Extender device, only 4 ports per switch are allowed in the port channel.

  • Port channel host interface—A port channel host interface for connection to a server or host system.

Fabric Interface Features


Note

Flow control is not supported on Cisco Nexus 2348TQ fabric extender.

Host Interfaces

Layer 3 Host Interfaces

Beginning with Cisco NX-OS Release 5.2, by default, all host interfaces on a Fabric Extender that are connected to a Cisco Nexus 7000 Series parent switch run in Layer 3 mode.


Note

If you have updated the parent switch to Cisco Nexus Release 5.2, previously configured fabric Extender host interfaces retain their default port mode, Layer 2. You can change these ports to Layer 3 mode with the no switchport command.

The host interfaces also support subinterfaces. You can create up to 63 subinterfaces on a Fabric Extender host interface.

Beginning with Cisco NX-OS Release 6.2, port profiles are supported on the host interfaces of a Fabric Extender.

For information about interfaces, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide.

Layer 2 Host Interfaces

Host Interface Port Channels

Layer 3 Host Interface Port Channels

The Fabric Extender (FEX) supports host interface port channel configurations. You can combine up to 8 interfaces in a standard mode port channel and 16 interfaces when configured with the Link Aggregation Control Protocol (LACP).


Note

Port channel resources are allocated when the port channel has one or more members.

All members of the port channel must be FEX host interfaces and all host interfaces must be from the same FEX. You cannot mix interfaces from the FEX and the parent switch.

Layer 3 mode is supported on host interface port channels.

A host interface port channel also supports subinterfaces. You can create up to 1000 subinterfaces on a FEX host interface port channel.

For more information about port channels, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide.

Layer 2 Host Interface Port Channels

The Fabric Extender supports host interface port channel configurations. You can combine up to 8 interfaces in a standard mode port channel and 16 interfaces when configured with the Link Aggregation Control Protocol (LACP).


Note

Port channel resources are allocated when the port channel has one or more members.

All members of the port channel must be Fabric Extender host interfaces and all host interfaces must be from the same Fabric Extender. You cannot mix interfaces from the Fabric Extender and the parent switch.

Layer 2 mode is supported on host interface port channels.

You can configure Layer 2 port channels as access or trunk ports.

Beginning with Cisco NX-OS Release 5.2(1), Fabric Extenders support the host vPC feature where a server can be dual-attached to two different FEXs through a port channel. You must configure parent switches that connect each Fabric Extender (one parent switch per FEX) in a vPC domain.

Minimum Number of Links on a Fabric Port Channel

In a network configuration of dual-homed hosts (active/standby), you can configure the Fabric Extender to support a minimum number of links for fabric port channels (FPCs) with the port-channel min-links command.

When the number of FPC links falls below the specified threshold, the host-facing Cisco Nexus 2000 interfaces are brought down. This process allows for a NIC switchover on the connection between the host and the FEX.

The automatic recovery of Cisco Nexus 2000 Series interfaces to the standby FEX is triggered when the number of FPC links reaches the specified threshold.

Load Balancing Using Host Interface Port Channels

The Cisco NX-OS software allows for load balancing traffic across all operational interfaces on a FEX host interface port-channel by hashing the addresses in the frame to a numerical value that selects one of the links in the channel. Port-channels provide load balancing by default.

You can configure the type of load-balancing algorithm used. You can choose the load-balancing algorithm that determines which member port to select for egress traffic by looking at the fields in the frame.

You can configure the load-balancing mode to apply to all Fabric Extenders or to specified ones. If load-balancing mode is not configured, Fabric Extenders use the default system configuration. The per-FEX configuration takes precedence over the load-balancing configuration for the entire system. You cannot configure the load-balancing method per port channel.


Note

The default load-balancing mode for Layer 3 interfaces is the source and destination IP address, and the default load-balancing mode for non-IP interfaces is the source and destination MAC address. For more details, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 6.x.

You can configure the device to use one of the following methods to load balance across the port channel:

  • Destination MAC address

  • Source MAC address

  • Source and destination MAC address

  • Destination IP address

  • Source IP address

  • Source and destination IP address

  • Source TCP/UDP port number

  • Destination TCP/UDP port number

  • Source and destination TCP/UDP port number

  • Dot1Q VLAN number


Note

You must be in the default virtual device context (VDC) to configure load-balancing method for FEX; if you attempt to configure this feature from another VDC, the system displays an error.

VLANs

The Fabric Extender supports Layer 2 VLAN trunks and IEEE 802.1Q VLAN encapsulation.

For more information about VLANs, see the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide.


Note

The Fabric Extender does not support private VLANs (PVLANs).

Protocol Offload

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

  • Link Layer Discovery Protocol (LLDP)

  • Cisco Discovery Protocol (CDP)

  • Link Aggregation Control Protocol (LACP)

Quality of Service

Access Control Lists

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

For more information about ACLs, see the Security Configuration Guide for your device.

IGMP Snooping

Switched Port Analyzer

Oversubscription

Management Model

The Cisco Nexus 2000 Series Fabric Extender is managed by its parent switch over the fabric interfaces through a zero-touch configuration model. The switch discovers the Fabric Extender by detecting the fabric interfaces of the Fabric Extender.

After discovery, if the Fabric Extender has been correctly associated with the parent switch, the following operations are performed:

  1. The switch checks the software image compatibility and upgrades the Fabric Extender if necessary.

  2. The switch and Fabric Extender establish in-band IP connectivity with each other.

  3. The switch pushes the configuration data to the Fabric Extender. The Fabric Extender does not store any configuration locally.

  4. The Fabric Extender updates the switch with its operational status. All Fabric Extender information is displayed using the switch commands for monitoring and troubleshooting.

Forwarding Model

The Cisco Nexus 2000 Series Fabric Extender does not perform any local switching. All traffic is sent to the parent switch that provides central forwarding and policy enforcement, including host-to-host communications between two systems that are connected to the same Fabric Extender as shown in the following figure.

Figure 1. Forwarding Model
Traffic between two hosts connected to the Fabric Extender is forwarded through the parent switch.

The forwarding model facilitates feature consistency between the Fabric Extender and its parent Cisco Nexus Series device.


Note

The Fabric Extender provides end-host connectivity into the network fabric. As a result, BPDU Guard is enabled on all its host interfaces. If you connect a bridge or switch to a host interface, that interface is placed in an error-disabled state when a BPDU is received.

You cannot disable BPDU Guard on the host interfaces of the Fabric Extender.

The Fabric Extender supports egress multicast replication from the network to the host. Packets that are sent from the parent switch for multicast addresses attached to the Fabric Extender are replicated by the Fabric Extender ASICs and are then sent to corresponding hosts.

Port Channel Fabric Interface Connection

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

Figure 2. Port Channel Fabric Interface Connection
An EtherChannel fabric interface bundles connections into a single logical channel.

When you configure the Fabric Extender to use a port channel 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 port channel does not trigger a change to the host interfaces. Traffic is automatically redistributed across the remaining links in the port channel fabric interface. If all links in the fabric port channel go down, all host interfaces on the FEX are set to the down state.

Port Numbering Convention

Fabric Extender Image Management

No software ships with the Cisco Nexus 2000 Series Fabric Extender. The Fabric Extender image is bundled into the system image of the parent switch. The image is automatically verified and updated (if required) during the association process between the parent switch and the Fabric Extender.

When you enter the install all command, it upgrades the software on the parent Cisco Nexus Series switch and also upgrades the software on any attached Fabric Extender. To minimize downtime as much as possible, the Fabric Extender remains online while the installation process loads its new software image. Once the software image has successfully loaded, the parent switch and the Fabric Extender both automatically reboot.

This process is required to maintain version compatibility between the parent switch and the Fabric Extender.

Licensing Requirements for the Fabric Extender

The following table shows the licensing requirements for the Cisco Nexus 2000 Series Fabric Extender:

Product

License Requirement

Cisco NX-OS

The Cisco Nexus 2000 Series Fabric Extender requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For an explanation of the licensing scheme, see the Cisco NX-OS Licensing Configuration Guide.

Guidelines and Limitations for the Fabric Extender

The Cisco Nexus 2000 Series Fabric Extender (FEX) has the following configuration guidelines and limitations:

  • Beginning with Cisco NX-OS Release 8.4(6), The Cisco Nexus 2248PQ, 2348TQ, 2348TQ-E, and 2348UPQ FEXs support using a QSA Adapter on the FEX NIF to connect to an 10G/SFP+ link on the parent switch.

  • Beginning with Cisco NX-OS Release 8.4(1), B22 Dell FEX is supported with F4-Series modules.

  • Beginning with Cisco NX-OS Release 5.2(1), the default port mode is Layer 3. Before Cisco NX-OS Release 5.2(1), the default port mode was Layer 2.

  • You must enable the Fabric Extender feature set in the default virtual device context (VDC). After you enable the feature set in the default VDC, the FEX can belong to any VDC and can be configured from those VDCs.

  • Each Fabric Extender that is connected to a chassis must have a unique FEX ID. The same FEX ID cannot be configured for two or more Fabric Extenders even if the Fabric Extenders are in separate VDCs.

  • The FEX ID for a Fabric Extender is persistent across a chassis. The FEX ID is not reset when used in a VDC.

  • All the uplinks and host ports of a Fabric Extender belong to a single VDC. The ports cannot be allocated or split among multiple VDCs.

  • The Fabric Extender feature set operation might cause the standby supervisor to reload if it is in an unstable state, such as following a service failure or powering up. You can check whether the standby supervisor is stable by using the show modules command. When the standby supervisor is stable, it is indicated as ha-standby.

  • You can configure the Fabric Extender host interfaces as edge ports only. The interface is placed in an error-disabled state if a downstream switch is detected.

  • The Fabric Extender does not support PVLANs.

  • For Cisco NX-OS Release 6.2(2) and later releases, the FEX supports queuing, which allows a router to be connected to a Layer 3 FEX interface or a router to be connected to a Layer 2 FEX interface (using SVI).

    Follow these guidelines for a router that is connected to a Layer 2 FEX interface (using SVI):

    • You can configure routing adjacency with Layer 3 on the peer router.

    • You can configure routing adjacency with SVI on the router using access/trunk interfaces.


      Note

      FEX interfaces do not support the spanning tree protocol.

      You must configure the network without the possibility of any loops.

  • For Cisco NX-OS Release 6.2(2) and later releases, the Cisco Fabric Extender supports routing protocol adjacency. Before Cisco NX-OS Release 6.2(2), the Fabric Extender cannot participate in a routing protocol adjacency with a device attached to its port. Only a static direct route is supported. This restriction applies to both of the following supported connectivity cases:

    • An SVI with a FEX single port or portchannel in Layer 2 mode.

    • A FEX port or portchannel in Layer 3 mode.

  • For Cisco NX-OS Release 6.2(2) and later releases, the Cisco Fabric Extender supports the following:

    • Queuing for Ethernet frames on a FEX-based CoS and DSCP values and support for queuing Fibre Channel over Ethernet (FCoE) frames on a FEX.

    • FEX HIF (FEX Host Interface) port to connect to a Protocol Independent Multicast (PIM) router.

  • For Cisco NX-OS Release 6.2(2) and later releases, the Cisco Fabric Extender supports optimized multicast flooding (OMF) is available on FEX ports.

  • The Cisco Fabric Extender does not support policy based routing (PBR).

    Beginning with Cisco NX-OS Release 6.2(2), the configured MTU for the FEX ports is controlled by the network QoS policy. To change the MTU that is configured on the FEX ports, modify the network QoS policy to change when the fabric port MTU is also changed.

  • In Cisco NX-OS Release 8.2(4), when you use the no negotiate auto command (for a FEX Host Interface (HIF) without a transceiver) after setting the speed to 1000, you get an error message as given below. This is a known limitation. 

    ERROR: Ethernet103/1/23: Configuration does not match the port capability.

Associating with F2-Series Modules

  • The following FEX devices support F2 modules:

    • 2248TP

    • 2248TP-E

    • 2248PQ

    • 2232TP

    • 2232PP

    • 2232TM

    • 2224TP

  • Each port in the ASIC has an index. Allow only ports with similar indices across ASICs to be added to a port channel.

    For example, if port 1 has an index of 1 and port 2 has an index of 2, the following ports are supported and not supported:

    • Supported: Port 1 of ASIC 1 and port 1 of ASIC 2 are added to a port channel.

    • Not supported: Port 1 of ASIC 1 and port 2 of ASIC 2 to form a port channel.

    A set of ports from an ASIC that has an index sub-set S, such as {1,2,4}, is allowed to be added to a port channel only if the port channel has an equivalent or an empty set.

FEX Queuing Support

  • FEX QoS Queuing Support

    Fabric Extenders (FEXs) follow the network quality of service (QoS) queuing model for supporting queuing on FEX host interfaces, regardless of whether the FEX is connected to M-series or F-series fabric uplinks.

    • Depending on the network-QoS template that is attached to the system QoS, the following parameters are inherited for queuing support on a FEX:

      • Number of queues

      • Class of service (CoS2q) mapping

      • Differentiated services code point (DSCP2q) mapping

      • Maximum transmission unit (MTU)

    • For both ingress and egress queuing on the FEX host interfaces, all of the preceding parameters are derived from the ingress queuing parameters that are defined in the active network-QoS policy. The egress queuing parameters of the active network-QoS policy do not affect the FEX host-port queuing.

    • Such parameters as the bandwidth, queue limit, priority, and set CoS in the network-QoS type queuing-policy maps are not supported for a FEX.

  • Hardware Queue-limit Support

    The following example shows how to configure the queue limit for a FEX by using the hardware fex-type queue-limit command in the FEX configuration mode: 

    switch(config)# fex 101
switch(config-fex)# hardware ?
  
  B22HP Fabric Extender 16x10G SFP+ 8x10G SFP+ Module
  N2224TP Fabric Extender 24x1G 2x10G SFP+ Module
  N2232P Fabric Extender 32x10G SFP+ 8x10G SFP+ Module
  N2232TM Fabric Extender 32x10GBase-T 8x10G SFP+ Module
  N2232TM-E Fabric Extender 32x10GBase-T 8x10G SFP+ Module
  N2248T Fabric Extender 48x1G 4x10G SFP+ Module
  N2248TP-E Fabric Extender 48x1G 4x10G SFP+ Module
switch(config-fex)# hardware N2248T ?
  queue-limit Set queue-limit
switch(config-fex)# hardware N2248T queue-limit ?
  <5120-652800> Queue limit in bytes ======> Allowed range of values varies dependent on the FEX type for which it is configured
switch(config-fex)# hardware N2248T queue-limit ======> Default configuration that sets queue-limit to default value of 66560 bytes
switch(config-fex)# hardware N2248T queue-limit 5120 ======> Set user defined queue-limit for FEX type N2248T associated on fex id 101
switch(config-fex)# no hardware N2248T queue-limit ======> Disable queue-limit for FEX type N2248T associated on fex id 101
switch(config-fex)# hardware N2248TP-E queue-limit ?
  <32768-33538048> Queue limit in Bytes
  rx Ingress direction
  tx Egress direction
switch(config-fex)# hardware N2248TP-E queue-limit 40000 rx
switch(config-fex)# hardware N2248TP-E queue-limit 80000 tx ======> For some FEX types, different queue-limit can be configured on ingress & egress directions

    The value of the queue limit that is displayed for a FEX interface is 0 bytes until after the first time the FEX interface is brought up. After the interface comes up, the output includes the default queue limit or the user-defined queue limit based on the hardware queue-limit configuration. If the hardware queue limit is unconfigured, “Queue limit: Disabled” is displayed in the command output. The following partial output of the show queuing interface interface command shows the queue limit that is enforced on a FEX: 

    switch# show queuing interface ethernet 101/1/48

<snippet>
Queue limit: 66560 bytes
<snippet>

  • Global Enable/Disable Control of DSCP2Q

    In the following example, the all or the f-series keyword enables DSCP2q mapping for the FEX host interfaces, regardless of the module type to which the FEX is connected: 

    switch(config)# hardware QoS dscp-to-queue ingress module-type ?
  all       Enable dscp based queuing for all cards
  f-series  Enable dscp based queuing for f-series cards
  m-series  Enable dscp based queuing for m-series cards

  • Show Command Support for FEX Host Interfaces

    The show queuing interface interface command is supported for FEX host interfaces. The following sample output of this command for FEX host interfaces includes the number of queues used, the mapping for each queue, the corresponding queue MTU, the enforced hardware queue limit, and the ingress and egress queue statistics.


    Note

    There is no support to clear the queuing statistics shown in this output. 

    switch# show queuing interface ethernet 199/1/2

slot  1
=======

Interface is not in this module.

slot  2
=======

Interface is not in this module.

slot  4
=======

Interface is not in this module.

slot  6
=======

Interface is not in this module.

slot  9
=======

Ethernet199/1/2 queuing information:
  Input buffer allocation:
  Qos-group: ctrl
  frh: 0
  drop-type: drop
  cos: 7
  xon       xoff      buffer-size
  ---------+---------+-----------
  2560      7680      10240

  Qos-group: 0  2  (shared)
  frh: 2
  drop-type: drop
  cos: 0 1 2 3 4 5 6
  xon       xoff      buffer-size
  ---------+---------+-----------
  34560     39680     48640

  Queueing:
  queue    qos-group    cos            priority  bandwidth mtu
  --------+------------+--------------+---------+---------+----
  ctrl-hi  n/a          7               PRI         0      2400
  ctrl-lo  n/a          7               PRI         0      2400
  2        0            0 1 2 3 4       WRR        80      1600
  4        2            5 6             WRR        20      1600

  Queue limit: 66560 bytes

  Queue Statistics:
  queue  rx              tx              flags
  ------+---------------+---------------+-----
  0      0               0                ctrl
  1      0               0                ctrl
  2      0               0                data
  4      0               0                data

  Port Statistics:
  rx drop         rx mcast drop   rx error        tx drop         mux ovflow
  ---------------+---------------+---------------+---------------+--------------
  0               0               0               0                InActive

  Priority-flow-control enabled: no
  Flow-control status: rx 0x0, tx 0x0, rx_mask 0x0
  cos     qos-group   rx pause  tx pause  masked rx pause
  -------+-----------+---------+---------+---------------
  0              0    xon       xon       xon
  1              0    xon       xon       xon
  2              0    xon       xon       xon
  3              0    xon       xon       xon
  4              0    xon       xon       xon
  5              2    xon       xon       xon
  6              2    xon       xon       xon
  7            n/a    xon       xon       xon

  DSCP to Queue mapping on FEX
----+--+-----+-------+--+---

FEX TCAM programmed successfully

  queue         DSCPs
-----          -----
02             0-39,
04             40-63,
03             **EMPTY**
05             **EMPTY**


slot 10
=======


slot 11
=======

Interface is not in this module.

slot 15
=======

Interface is not in this module.

slot 16
=======

Interface is not in this module.

slot 17
=======

Interface is not in this module.

slot 18
=======

Interface is not in this module.

  • ISSU Behavior

    In Cisco NX-OS Release 6.2(2) and later releases, FEX queuing is disabled by default on all existing FEXs after an in-service software upgrade (ISSU). FEX queuing is enabled upon flapping the FEX. You can reload the FEX to enable queuing on any FEX after an ISSU. A message is displayed in the output of the show queuing interface interface command for the FEX host interface after an ISSU. 

    switch# show queuing interface ethernet 133/1/32 module 9

Ethernet133/1/32 queuing information:
  Input buffer allocation:
  Qos-group: ctrl
  frh: 0
  drop-type: drop
  cos: 7
  xon       xoff      buffer-size
  ---------+---------+-----------
  2560      7680      10240

  Qos-group: 0
  frh: 8
  drop-type: drop
  cos: 0 1 2 3 4 5 6
  xon       xoff      buffer-size
  ---------+---------+-----------
  0         126720    151040

  Queueing:
  queue    qos-group    cos            priority  bandwidth mtu
  --------+------------+--------------+---------+---------+----
  ctrl-hi  n/a          7               PRI         0      2400
  ctrl-lo  n/a          7               PRI         0      2400
  2        0            0 1 2 3 4 5 6   WRR       100      9440

  Queue limit: 66560 bytes

  Queue Statistics:
  queue  rx              tx              flags
  ------+---------------+---------------+-----
  0      0               0                ctrl
  1      0               0                ctrl
  2      0               0                data

  Port Statistics:
 rx drop         rx mcast drop   rx error        tx drop         mux ovflow
  ---------------+---------------+---------------+---------------+--------------
  0               0               0               0                InActive

  Priority-flow-control enabled: no
  Flow-control status: rx 0x0, tx 0x0, rx_mask 0x0
  cos     qos-group   rx pause  tx pause  masked rx pause
  -------+-----------+---------+---------+---------------
  0              0    xon       xon       xon
  1              0    xon       xon       xon
  2              0    xon       xon       xon
  3              0    xon       xon       xon
  4              0    xon       xon       xon
  5              0    xon       xon       xon
  6              0    xon       xon       xon
  7            n/a    xon       xon       xon

 ***FEX queuing disabled on fex 133. Reload the fex to enable queuing.<======

    For any new FEXs brought online after an ISSU, queuing is enabled by default.

    The queue limit is enabled by default for all FEXs, regardless of whether queuing is enabled or disabled for the FEX. In Cisco NX-OS Release 6.2(2), all FEXs come up with the default hardware queue-limit value. Any user-defined queue limit that is configured after an ISSU by using the hardware queue-limit command takes effect even if queuing is not enabled for the FEX.

  • No Support on the Cisco Nexus 2248PQ 10-Gigabit Ethernet Fabric Extender

    The following sample output shows that FEX queuing is not supported for the Cisco Nexus 2248PQ 10-Gigabit Ethernet Fabric Extender (FEX2248PQ): 

    switch# show queuing interface ethernet 143/1/1 module 5

Ethernet143/1/1 queuing information:
Network-QOS is disabled for N2248PQ <=======
Displaying the default configurations
  Input buffer allocation:
  Qos-group: ctrl
  frh: 0
  drop-type: drop
  cos: 7
  xon       xoff      buffer-size
  ---------+---------+-----------
  2560      7680      10240

  Qos-group: 0
  frh: 8
  drop-type: drop
  cos: 0 1 2 3 4 5 6
  xon       xoff      buffer-size
  ---------+---------+-----------
  0         126720    151040

  Queueing:
  queue    qos-group    cos            priority  bandwidth mtu
  --------+------------+--------------+---------+---------+----
  ctrl-hi  n/a          7               PRI         0      2400
  ctrl-lo  n/a          7               PRI         0      2400
  2        0            0 1 2 3 4 5 6   WRR       100      9440

  Queue limit: 0 bytes

  Queue Statistics:
  queue  rx              tx              flags
  ------+---------------+---------------+-----
  0      0               0                ctrl
  1      0               0                ctrl
  2      0               0                data

  Port Statistics:
  rx drop         rx mcast drop   rx error        tx drop         mux ovflow
  ---------------+---------------+---------------+---------------+--------------
  0               0               0               0                InActive

  Priority-flow-control enabled: no
  Flow-control status: rx 0x0, tx 0x0, rx_mask 0x0
  cos     qos-group   rx pause  tx pause  masked rx pause
  -------+-----------+---------+---------+---------------
  0              0    xon       xon       xon
  1              0    xon       xon       xon
  2              0    xon       xon       xon
  3              0    xon       xon       xon
  4              0    xon       xon       xon
  5              0    xon       xon       xon
  6              0    xon       xon       xon
  7            n/a    xon       xon       xon

  • Fabric Port Queuing Restrictions

    • For FEXs that are connected to M-series uplinks, the queuing structure is different on FEX host interfaces and FEX fabric interfaces. The M series queuing policies must be consistent with the FEX queuing policies.

  • MTU

    • FEX queue MTU configurations are derived from type network-QoS policy-map templates. MTU changes are applied on cloned network-QoS policy maps. The MTU that is configured on a FEX port must match the MTU in the network-QoS policy map so that the FEX MTU can be applied to the FEX host interfaces. For more information, see the Cisco Nexus 7000 Series NX-OS Quality of Service Configuration Guide.


      Note

      Starting with Cisco NX-OS Release 6.2(2), the configured MTU for the FEX ports is controlled by the network QoS policy. To change the MTU that is configured on the FEX ports, modify the network QoS policy to change when the fabric port MTU is also changed.

      If you change the FEX fabric port MTU on a version prior to Cisco NX-OS Release 6.2(x), and then upgrade via ISSU to Cisco NX-OS Release 6.2(x) or a later version, you will not get any issues until either a FEX or switch is reloaded. It is recommended that post-upgrade, the FEX HIF MTU be changed via the network QoS policy as described above.

      Qos policy changes affects only F series cards and M series cards.

Configuration Limits

The configuration limits are documented in the Cisco Nexus 7000 Series NX-OS Verified Scalability Guide.

Default Settings

This table lists the default settings for the Fabric Extender parameters.

Table 1. Default Cisco Nexus 2000 Series Fabric Extender Parameter Settings

Parameters

Default

feature-set fex command

Disabled

Port mode

Layer 3 (Cisco NX-OS Release 5.2 and later releases).

Layer 2 (Cisco NX-OS Release 5.1 and earlier releases).