Configuring Unidirectional Ethernet

This chapter describes how to configure Unidirectional Ethernet on the Cisco Nexus 9000 series switches.

Unidirectional Ethernet (UDE) Overview

Unidirectional Ethernet uses only one strand of fiber for either transmitting or receiving one-way traffic, instead of two strands of fiber.

With unidirectional links either transmit or receive traffic for applications, such as video streaming, where most traffic sent is unacknowledged.You can create a unidirectional link by configuring ports equipped with bidirectional transceivers to unidirectionally transmit or receive traffic. You can use UDE when there is no appropriate unidirectional transceiver available. For example, without supported transmit-only transceivers, you must configure transmit-only links with software-based UDE.

In certain cases, it's required to block all the control traffic egressing out of the interface to avoid network outage. You can achieve this by using the QoS template to block all the egress traffic on selected Ethernet ports.

Guidelines and Limitations for Unidirectional Ethernet

  • UDE send-only is supported.

  • UDE receive-only is not supported till Cisco NX-OS Release 10.1(1).

  • Beginning with Cisco NX-OS Release 10.1(2), UDE receive-only is also supported.

  • Beginning with Cisco NX-OS Release 10.1(2), UDE is supported on N9K-X9624D-R2, N9K-X9636Q-R, N9K-X9636C-RX, N9K-X96136YC-R, N9K-X9624D-R2, N9K-X9636C-R, Cisco Nexus 3636C-R, and Cisco Nexus 36180YC-R modules.

  • UDE can be enabled on all ports simultaneously.

  • UDE on breakout is supported from Cisco NX-OS Release 10.1(1) and later releases.

  • UDE at hardware level is supported only on Cisco Nexus 9500 switches with X97160YC-EX line cards.

  • UDE is supported only for native 10G-LR/10G-LRS transceivers, and cannot be used with QSAs or breakout cables.

  • Beginning with Cisco NX-OS Release 10.1(1), UDE is supported on the N9K-C9336C-FX2, N9KC93240YC-FX2, N9K-C93180YC-FX, N9K-C93360YC-FX2 TORs and N9K-X97160YC-EX line card.

  • Beginning with Cisco NX-OS Release 10.1(1), UDE supports the following transceivers: 10G-SR, 10G-AOC, 40G-SR, 40G-LR, 40G-AOC, 100G-SR, 100G-LR, and 100G-AOC.

  • Port flap may occur when you configure UDE on a port.

  • You can add physical interfaces with and without UDE configuration into a port-channel. However, you must ensure only send-only interfaces are added to a port-channel. UDE may not work as expected if you mix send-only configuration with other interfaces.

  • The port-channel may not receive packets if all members are configured as UDE send-only.

  • The port-channel may not receive packets if all members are configured as UDE send-only which can prevent LCAP based port-channel to come up.

  • Special control plane traffic pruning is not configured on send-only ports.

  • Unidirectional ports do not support any features or protocols that require negotiation with the port at the other end of the link. You must disable all features that require bi-directional communication.

Guidelines for UDE Policers

Beginning with Cisco NX-OS Release 10.3(3), QoS template based UDE is supported. These are the guidelines and limitations for UDE policers.

  • UDE template should be enabled only on L2 interfaces, and port should be in mode tap-aggregation.

  • Policy-map default-ndb-out-policy is not supported under system QoS.

  • To support this feature, you need to carve the egress Layel2 QoS TCAM region.

  • On reboot, the switch may take some time to apply the default-ndb-out-policy to the configured interface. Due to this, few packets may get leaked. Subsequently, all egress control/flood traffic are dropped.

  • Even if there is no data traffic, control traffic such as CDP, LLDP, ARP, BPDU and so on from CPU will hit ACL entry and get dropped, incrementing the violated count. This is expected behavior when default-ndb-out-policy is configured.

Configuring Unidirectional Ethernet

To configure unidirectional ethernet, follow these steps:

SUMMARY STEPS

  1. configure terminal
  2. interface ethernet {type slot /port}
  3. unidirectional send-only
  4. unidirectional receive-only
  5. exit
  6. show running-config interface {type slot /port}
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface ethernet {type slot /port}

Example:

switch(config)# interface ethernet 3/1

Specifies an interface to configure, and enters interface configuration mode.

Step 3

unidirectional send-only

Example:

switch(config)# unidirectional send-only

Configures uni-directional transmit (send only) mode.

Step 4

unidirectional receive-only

Example:

switch(config)# unidirectional receive-only

Configures uni-directional transmit (receive only) mode.

Step 5

exit

Example:

switch(config)# exit

Exits interface mode.

Step 6

show running-config interface {type slot /port}

Example:

switch(config)# show running-config interface ethernet 3/1

Displays configuration information about the specified interface.

Step 7

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

Copies the running configuration to the startup configuration

Configuring UDE Policers

To configure unidirectional ethernet using QoS template, follow these steps.

SUMMARY STEPS

  1. hardware access-list tcam region egr-l2-qos 256 copy run start reload
  2. interface type slot/port
  3. interface Ethernet1/22 service-policy type qos output default-ndb-out-policy

DETAILED STEPS

  Command or Action Purpose

Step 1

hardware access-list tcam region egr-l2-qos 256 copy run start reload

Example:

art does not have any config

TCAM carving.

Step 2

interface type slot/port

Example:

switch(config)# interface ethernet 2/5
switch(config-if)#

Enters interface mode on the interface specified.

Step 3

interface Ethernet1/22 service-policy type qos output default-ndb-out-policy

Block all the egress traffic on selected Ethernet ports.

Example

Execute the following command to see default-ndb-out-policy output:


switch# show policy-map type qos default-ndb-out-policy
Type qos policy-maps
====================
policy-map type qos default-ndb-out-policy
class class-ndb-default
police cir 0 bps conform transmit violate drop
N9K#

Execute the following command to get the UDE policer stats:


switch# sh policy-map interface ethernet 1/6 output type qos
Global statistics status : enabled
Ethernet1/6
Service-policy (qos) output: default-ndb-out-policy
SNMP Policy Index: 285213501
Class-map (qos): class-ndb-default (match-any)
Slot 1
61211339 packets 15669992128 bytes
5 minute offered rate 17721223780 bps
Aggregate forwarded :
61211339 packets 110848 bytes
police cir 0 bps
conformed 0 bytes, n/a bps action: transmit
violated 15669881280 bytes, n/a bps action: drop
UDE-CF#