Configuring EtherChannels
This chapter describes how to configure EtherChannels
and to apply and configure the Link Aggregation Control Protocol (LACP) for
more efficient use of EtherChannels in
Cisco NX-OS.
It contains the following sections:
Information About EtherChannels
An EtherChannel bundles up to 16 individual
interfaces into a group to provide increased bandwidth and redundancy. Port
channeling also load balances traffic across these physical interfaces. The
EtherChannel stays operational as long as at least one physical interface
within the EtherChannel is operational.
You create an EtherChannel by bundling compatible
interfaces. You can configure and run either static EtherChannels or
EtherChannels running the Link Aggregation Control Protocol (LACP).
Any configuration changes that you apply to the
EtherChannel are applied to each member interface of that EtherChannel. For
example, if you configure Spanning Tree Protocol (STP) parameters on the
EtherChannel, the
Cisco NX-OS
applies those parameters to each interface in the EtherChannel.
You can use static EtherChannels, with no
associated protocol, for a simplified configuration. For more efficient use of
the EtherChannel, you can use the Link Aggregation Control Protocol (LACP),
which is defined in IEEE 802.3ad. When you use LACP, the link passes protocol
packets.
Understanding EtherChannels
Using EtherChannels,
Cisco NX-OS
provides wider bandwidth, redundancy, and load balancing across the channels.
You can collect up to 16 ports into a static
EtherChannel or you can enable the Link Aggregation Control Protocol (LACP).
Configuring EtherChannels with LACP requires slightly different steps than
configuring static EtherChannels.
 Note |
Cisco NX-OS
does not support Port Aggregation Protocol (PAgP) for EtherChannels.
|
An EtherChannel bundles individual links into a
channel group to create a single logical link that provides the aggregate
bandwidth of up to 16 physical links. If a member port within an EtherChannel
fails, traffic previously carried over the failed link switches to the
remaining member ports within the EtherChannel.
Each port can be in only one EtherChannel. All the
ports in an EtherChannel must be compatible; they must use the same speed and
operate in full-duplex mode. When you are running static EtherChannels, without
LACP, the individual links are all in the on channel mode; you cannot change
this mode without enabling LACP.
 Note |
You cannot change the mode from ON to Active or
from ON to Passive.
|
You can create an EtherChannel directly by creating
the port-channel interface, or you can create a channel group that acts to
aggregate individual ports into a bundle. When you associate an interface with
a channel group,
Cisco NX-OS
creates a matching EtherChannel automatically if the EtherChannel does not
already exist. You can also create the EtherChannel first. In this instance,
Cisco NX-OS
creates an empty channel group with the same channel number as the EtherChannel
and takes the default configuration.
 Note |
An EtherChannel is operationally up when at least
one of the member ports is up and that port’s status is channeling. The
EtherChannel is operationally down when all member ports are operationally
down.
|
Compatibility Requirements
When you add an interface to a channel group,
Cisco NX-OS
checks certain interface attributes to ensure that the interface is compatible
with the channel group.
Cisco NX-OS
also checks a number of operational attributes for an interface before allowing
that interface to participate in the port-channel aggregation.
The compatibility check includes the following
operational attributes:
-
Port mode
-
Access VLAN
-
Trunk native VLAN
-
Allowed VLAN list
-
Speed
-
802.3x flow control setting
-
MTU
The
Cisco Nexus 5000 Series
switch only supports system level MTU. This attribute cannot be changed on an
individual port basis.
-
Broadcast/Unicast/Multicast Storm Control
setting
-
Priority-Flow-Control
-
Untagged CoS
Use the
show port-channel
compatibility-parameters command to see the full list of
compatibility checks that
Cisco NX-OS
uses.
You can only add interfaces configured with the
channel mode set to
on to static EtherChannels.
You can also only add interfaces configured with the channel mode as
active or
passive to EtherChannels
that are running LACP. You can configure these attributes on an individual
member port.
When the interface joins an EtherChannel, the
following individual parameters are replaced with the values on the
EtherChannel:
-
Bandwidth
-
MAC address
-
Spanning Tree Protocol
The following interface parameters remain
unaffected when the interface joins an EtherChannel:
-
Description
-
CDP
-
LACP port priority
-
Debounce
Load Balancing Using EtherChannels
Cisco NX-OS load balances traffic
across all operational interfaces in an EtherChannel by reducing part of the
binary pattern formed from the addresses in the frame to a numerical value that
selects one of the links in the channel. EtherChannels provide load balancing
by default and the basic configuration uses the following criteria to select
the link:
-
For a Layer 2 frame, it uses the source and destination MAC
addresses.
-
For a Layer 3 frame, it uses the source and destination MAC
addresses and the source and destination IP addresses.
-
For a Layer 4 frame, it uses the source and destination MAC
addresses, the source and destination IP addresses, and the source and
destination port number.
You can configure the switch to use one of the following methods to
load balance across the EtherChannel:
-
Destination MAC address
-
Source MAC address
-
Source and destination MAC address
-
Destination IP address
-
Source IP address
-
Source and destination IP address
-
Destination TCP/UDP port number
-
Source TCP/UDP port number
-
Source and destination TCP/UDP port number
The following table shows the criteria used for each configuration:
Table 1 EtherChannel Load-Balancing Criteria
Configuration
|
Layer 2 Criteria
|
Layer 3 Criteria
|
Layer 4 Criteria
|
Destination MAC
|
Destination MAC
|
Destination MAC
|
Destination MAC
|
Source MAC
|
Source MAC
|
Source MAC
|
Source MAC
|
Source and destination MAC
|
Source and destination MAC
|
Source and destination MAC
|
Source and destination MAC
|
Destination IP
|
Destination MAC
|
Destination MAC, destination IP
|
Destination MAC, destination IP
|
Source IP
|
Source MAC
|
Source MAC, source IP
|
Source MAC, source IP
|
Source and destination IP
|
Source and destination MAC
|
Source and destination MAC, source and destination IP
|
Source and destination MAC, source and destination IP
|
Destination TCP/UDP port
|
Destination MAC
|
Destination MAC, destination IP
|
Destination MAC, destination IP, destination port
|
Source TCP/UDP port
|
Source MAC
|
Source MAC, source IP
|
Source MAC, source IP, source port
|
Source and destination TCP/UDP port
|
Source and destination MAC
|
Source and destination MAC, source and destination IP
|
Source and destination MAC, source and destination IP, source
and destination port
|
Use the option that provides the balance criteria with the greatest
variety in your configuration. For example, if the traffic on an EtherChannel
is going only to a single MAC address and you use the destination MAC address
as the basis of port-channel load balancing, the EtherChannel always chooses
the same link in that EtherChannel; using source addresses or IP addresses
might result in better load balancing.
Understanding LACP
LACP Overview
 Note |
You must enable the LACP feature before you can configure and use LACP
functions.
|
The following figure shows how individual links can be combined into
LACP EtherChannels and channel groups as well as function as individual links.
Figure 1. Individual Links Combined into an EtherChannel
With LACP, you can bundle up to 16 interfaces in a channel group.
 Note |
When you delete the EtherChannel,
Cisco NX-OS automatically deletes
the associated channel group. All member interfaces revert to their previous
configuration.
|
You cannot disable LACP while any LACP configurations are present.
LACP ID Parameters
LACP uses the following parameters:
-
LACP system priority—Each system that runs LACP has an LACP system
priority value. You can accept the default value of 32768 for this parameter,
or you can configure a value between 1 and 65535. LACP uses the system priority
with the MAC address to form the system ID and also uses the system priority
during negotiation with other devices. A higher system priority value means a
lower priority.
 Note |
The LACP system ID is the combination of the LACP system priority
value and the MAC address.
|
-
LACP port priority—Each port configured to use LACP has an LACP
port priority. You can accept the default value of 32768 for the LACP port
priority, or you can configure a value between 1 and 65535. LACP uses the port
priority with the port number to form the port identifier. LACP uses the port
priority to decide which ports should be put in standby mode when there is a
limitation that prevents all compatible ports from aggregating and which ports
should be put into active mode. A higher port priority value means a lower
priority for LACP. You can configure the port priority so that specified ports
have a lower priority for LACP and are most likely to be chosen as active
links, rather than hot-standby links.
-
LACP administrative key—LACP automatically configures an
administrative key value equal to the channel-group number on each port
configured to use LACP. The administrative key defines the ability of a port to
aggregate with other ports. A port’s ability to aggregate with other ports is
determined by these factors:
-
Port physical characteristics, such as the data rate, the
duplex capability, and the point-to-point or shared medium state
-
Configuration restrictions that you establish
Channel Modes
Individual interfaces in EtherChannels are configured with channel
modes. When you run static EtherChannels, with no protocol, the channel mode is
always set to
on. After you enable LACP globally on the device,
you enable LACP for each channel by setting the channel mode for each interface
to
active or
passive. You can configure either channel mode for
individual links in the LACP channel group.
 Note |
You must enable LACP globally before you can configure an interface
in either the
active or
passive channel mode.
|
The following table describes the channel modes.
Table 2 Channel Modes for Individual Links in an EtherChannel
Channel Mode
|
Description
|
passive
|
LACP mode that places a port into a passive negotiating state,
in which the port responds to LACP packets that it receives but does not
initiate LACP negotiation.
|
active
|
LACP mode that places a port into an active negotiating state,
in which the port initiates negotiations with other ports by sending LACP
packets.
|
on
|
All static EtherChannels, that is, that are not running LACP,
remain in this mode. If you attempt to change the channel mode to active or
passive before enabling LACP, the device returns an error message.
You enable LACP on each channel by configuring the interface
in that channel for the channel mode as either
active or
passive. When an LACP attempts to negotiate
with an interface in the
on state, it does not receive any LACP
packets and becomes an individual link with that interface; it does not join
the LACP channel group.
|
Both the passive and active modes allow LACP to negotiate between
ports to determine if they can form an EtherChannel, based on criteria such as
the port speed and the trunking state. The passive mode is useful when you do
not know whether the remote system, or partner, supports LACP.
Ports can form an LACP EtherChannel when they are in different LACP
modes as long as the modes are compatible as in the following examples:
-
A port in active mode can form an EtherChannel successfully with
another port that is in active mode.
-
A port in active mode can form an EtherChannel with another port
in passive mode.
-
A port in passive mode cannot form an EtherChannel with another
port that is also in passive mode because neither port will initiate
negotiation.
-
A port in on mode is not running LACP.
LACP Marker Responders
Using EtherChannels, data traffic may be dynamically redistributed due to either a link failure or load balancing. LACP uses the Marker Protocol to ensure that frames are not duplicated or reordered because of this redistribution.
Cisco NX-OS supports only Marker Responders.
LACP-Enabled and Static EtherChannels Differences
The following table provides a brief summary of major differences
between EtherChannels with LACP enabled and static EtherChannels.
Table 3 EtherChannels with LACP Enabled and Static EtherChannels
Configurations
|
EtherChannels with LACP Enabled
|
Static EtherChannels
|
Protocol applied
|
Enable globally.
|
Not applicable.
|
Channel mode of links
|
Can be either:
|
Can only be On.
|
Maximum number of links in channel
|
16
|
16
|
Configuring EtherChannels
Creating an EtherChannel
You can create an EtherChannel before creating a
channel group.
Cisco NX-OS
automatically creates the associated channel group.
 Note |
If you want LACP-based EtherChannels, you need to
enable LACP.
|
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
interface port-channel
channel-number
3.
switch(config)#
no interface
port-channel
channel-number
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
interface port-channel
channel-number
|
Specifies the port-channel interface to
configure, and enters the interface configuration mode. The range is from 1 to
4096.
Cisco NX-OS
automatically creates the channel group if it does not already exist.
|
Step 3 |
switch(config)#
no interface
port-channel
channel-number
|
Removes the EtherChannel and deletes the
associated channel group.
|
This example shows how to create an EtherChannel:
switch# configure terminal
switch (config)# interface port-channel 1
Adding a Port to an EtherChannel
You can add a port to a new channel group or to a
channel group that already contains ports.
Cisco NX-OS
creates the EtherChannel associated with this channel group if the EtherChannel
does not already exist.
 Note |
If you want LACP-based EtherChannels, you need to
enable LACP.
|
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
interface
type
slot/port
3.
(Optional)
switch(config-if)#
switchport mode trunk
4.
(Optional)
switch(config-if)#
switchport trunk {allowed vlan
vlan-id |
native vlan
vlan-id}
5.
switch(config-if)#
channel-group
channel-number
6.
(Optional)
switch(config-if)#
no channel-group
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
interface
type
slot/port
|
Specifies the interface that you want to add to
a channel group and enters the interface configuration mode.
|
Step 3 |
switch(config-if)#
switchport mode trunk
| (Optional)
Configures the interface as a trunk port.
|
Step 4 |
switch(config-if)#
switchport trunk {allowed vlan
vlan-id |
native vlan
vlan-id}
| (Optional)
Configures necessary parameters for a trunk
port.
|
Step 5 |
switch(config-if)#
channel-group
channel-number
|
Configures the port in a channel group and sets
the mode. The channel-number range is from 1 to 4096.
Cisco NX-OS
creates the EtherChannel associated with this channel group if the EtherChannel
does not already exist. This is called implicit
EtherChannel creation.
|
Step 6 |
switch(config-if)#
no channel-group
| (Optional)
Removes the port from the channel group. The
port reverts to its original configuration.
|
This example shows how to add an Ethernet interface
1/4 to channel group 1:
switch# configure terminal
switch (config)# interface ethernet 1/4
switch(config-if)# switchport mode trunk
switch(config-if)# channel-group 1
Configuring Load Balancing Using
EtherChannels
You can configure the load-balancing algorithm for
EtherChannels that applies to the entire device.
 Note |
If you want LACP-based EtherChannels, you need to
enable LACP.
|
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
port-channel load-balance
ethernet {destination-ip |
destination-mac |
destination-port |
source-dest-ip |
source-dest-mac |
source-dest-port |
source-ip |
source-mac |
source-port}
3.
(Optional)
switch(config)#
no port-channel load-balance
ethernet
4.
(Optional)
switch(config-router)#
show port-channel
load-balance
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
port-channel load-balance
ethernet {destination-ip |
destination-mac |
destination-port |
source-dest-ip |
source-dest-mac |
source-dest-port |
source-ip |
source-mac |
source-port}
|
Specifies the load-balancing algorithm for the
device. The range depends on the device. The default is source-dest-mac.
|
Step 3 |
switch(config)#
no port-channel load-balance
ethernet
| (Optional)
Restores the default load-balancing algorithm
of
source-dest-mac.
|
Step 4 |
switch(config-router)#
show port-channel
load-balance
| (Optional)
Displays the port-channel load-balancing
algorithm.
|
This example shows how to configure source IP load
balancing for EtherChannels:
switch# configure terminal
switch (config)# port-channel load-balance ethernet source-ip
 Note |
Before Release 4.0(1a)N1 of
Cisco NX-OS,
the
source-dest-ip,
source-dest-mac, and
source-dest-port keywords
were
source-destination-ip,
source-destination-mac,
and
source-destination-port,
respectively.
|
Enabling LACP
LACP is disabled by default; you must enable LACP before you begin
LACP configuration. You cannot disable LACP while any LACP configuration is
present.
LACP learns the capabilities of LAN port groups dynamically and
informs the other LAN ports. Once LACP identifies correctly matched Ethernet
links, it facilitates grouping the links into an EtherChannel. The EtherChannel
is then added to the spanning tree as a single bridge port.
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
feature lacp
3.
(Optional)
switch(config)#
show feature
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
feature lacp
|
Enables LACP on the switch.
|
Step 3 |
switch(config)#
show feature
| (Optional)
Displays enabled features.
|
This example shows how to enable LACP:
switch# configure terminal
switch(config)# feature lacp
Configuring Channel Mode for a Port
You can configure the channel mode for each individual link in the
LACP EtherChannel as
active or
passive. This channel configuration mode allows the
link to operate with LACP.
When you configure EtherChannels with no associated protocol, all
interfaces on both sides of the link remain in the
on channel mode.
Before You Begin
Ensure that you have enabled the LACP feature.
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
interface
type
slot/port
3.
switch(config-if)#
channel-group
number
mode {active |
on |
passive}
4.
switch(config-if)#
no channel-group
number
mode
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
interface
type
slot/port
|
Specifies the interface to configure, and enters the interface
configuration mode.
|
Step 3 |
switch(config-if)#
channel-group
number
mode {active |
on |
passive}
|
Specifies the port mode for the link in an EtherChannel. After
LACP is enabled, you configure each link or the entire channel as active or
passive.
When you run EtherChannels with no associated protocol, the
channel mode is always
on.
The default channel mode is on.
|
Step 4 |
switch(config-if)#
no channel-group
number
mode
|
Returns the port mode to on for the specified interface.
|
This example shows how to set the LACP-enabled interface to active
port-channel mode for Ethernet interface 1/4 in channel group 5:
switch# configure terminal
switch (config)# interface ethernet 1/4
switch(config-if)# channel-group 5 mode active
Configuring the LACP System Priority and System ID
The LACP system ID is the combination of the LACP system priority
value and the MAC address.
Before You Begin
Ensure that you have enabled the LACP feature.
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
lacp system-priority
priority
3.
(Optional)
switch#
show lacp system-identifier
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
lacp system-priority
priority
|
Configures the system priority for use with LACP. Valid values are
1 through 65535, and higher numbers have lower priority. The default value is
32768.
|
Step 3 |
switch#
show lacp system-identifier
| (Optional)
Displays the LACP system identifier.
|
This example shows how to set the LACP system priority to 2500:
switch# configure terminal
switch(config)# lacp system-priority 2500
Configuring the LACP Port Priority
You can configure each link in the LACP EtherChannel for the port
priority.
Before You Begin
Ensure that you have enabled the LACP feature.
SUMMARY STEPS1.
switch#
configure terminal
2.
switch(config)#
interface
type
slot/port
3.
switch(config-if)#
lacp port-priority
priority
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode.
|
Step 2 |
switch(config)#
interface
type
slot/port
|
Specifies the interface to configure, and enters the interface
configuration mode.
|
Step 3 |
switch(config-if)#
lacp port-priority
priority
|
Configures the port priority for use with LACP. Valid values are 1
through 65535, and higher numbers have lower priority. The default value is
32768.
|
This example shows how to set the LACP port priority for Ethernet
interface 1/4 to 40000:
switch# configure terminal
switch (config)# interface ethernet 1/4
switch(config-if)# lacp port priority 40000
Verifying EtherChannel Configuration
To display EtherChannel configuration information, perform one of the
following tasks:
Command
|
Purpose
|
switch#
show interface port-channel
channel-number
|
Displays the status of a EtherChannel interface.
|
switch#
show feature
|
Displays enabled features.
|
switch#
show resource
|
Displays the number of resources currently available in the
system.
|
switch#
show lacp {counters |
interface
type
slot/port |
neighbor |
port-channel |
system-identifier}
|
Displays LACP information.
|
switch#
show port-channel compatibility-parameters
|
Displays the parameters that must be the same among the
member ports in order to join an EtherChannel.
|
switch#
show port-channel database [interface
port-channel
channel-number]
|
Displays the aggregation state for one or more port-channel
interfaces.
|
switch#
show port-channel summary
|
Displays a summary for the EtherChannel interfaces.
|
switch#
show port-channel traffic
|
Displays the traffic statistics for EtherChannels.
|
switch#
show port-channel usage
|
Displays the range of used and unused channel numbers.
|
switch#
show port-channel database
|
Displays information on current running of the EtherChannel
feature.
|
switch#
show port-channel load-balance
|
Displays information about load-balancing using
EtherChannels.
|