Understanding EtherChannels
An EtherChannel consists of individual Fast Ethernet or Gigabit Ethernet links bundled into a single logical link as shown in Figure 29-1.
The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast
EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and
another switch or host.
Figure 29-1 Typical EtherChannel Configuration
Each EtherChannel can consist of up to eight compatibly configured
Ethernet interfaces. All interfaces in each EtherChannel must be the
same speed, and all must be configured as either Layer 2 or Layer 3
interfaces.
If a link within an EtherChannel fails, traffic previously carried over
that failed link changes to the remaining links within the EtherChannel.
A trap is sent for a failure, identifying the switch, the EtherChannel,
and the failed link. Inbound broadcast and multicast packets on one
link in an EtherChannel are blocked from returning on any other link of
the EtherChannel.
Understanding Port-Channel Interfaces
You create an EtherChannel for Layer 2 interfaces differently from Layer
3 interfaces. Both configurations involve logical interfaces.
•
With Layer 3 interfaces, you manually create the logical interface by using the interface port-channel global configuration command.
With Layer 3 interfaces, you manually create the logical interface by using the interface port-channel global configuration command.
•With Layer 2 interfaces, the logical interface is dynamically created.
With Layer 2 interfaces, the logical interface is dynamically created.
•With both Layer 3 and 2 interfaces, you manually assign an interface to the EtherChannel by using the channel-group interface configuration command. This command binds the physical and logical ports together as shown in Figure 29-2.
With both Layer 3 and 2 interfaces, you manually assign an interface to the EtherChannel by using the channel-group interface configuration command. This command binds the physical and logical ports together as shown in Figure 29-2.
Each EtherChannel has a logical port-channel interface numbered from 1 to 64. The channel groups are also numbered from 1 to 64.
Figure 29-2 Relationship of Physical Ports, Logical Port Channels, and Channel Groups
When a port joins an EtherChannel, the physical interface for that port
is shut down. When the port leaves the port-channel, its physical
interface is brought up, and it has the same configuration as it had
before joining the EtherChannel.
Understanding the Port Aggregation Protocol and Link Aggregation Protocol
The Port Aggregation Protocol (PAgP) and Link Aggregation Control
Protocol (LACP) facilitate the automatic creation of EtherChannels by
exchanging packets between Ethernet interfaces. PAgP is a
Cisco-proprietary protocol that can be run only on Cisco switches and on
those switches licensed by licensed vendors to support PAgP. LACP is
defined in IEEE 802.3AD and allows Cisco switches to manage Ethernet
channels between switches that conform to the 802.3AD protocol.
By using one of these protocols, a switch learns the identity of
partners capable of supporting either PAgP or LACP and learns the
capabilities of each interface. It then dynamically groups similarly
configured interfaces into a single logical link (channel or aggregate
port); these interfaces are grouped based on hardware, administrative,
and port parameter constraints. For example, PAgP groups the interfaces
with the same speed, duplex mode, native VLAN, VLAN range, and trunking
status and type. After grouping the links into an EtherChannel, PAgP
adds the group to the spanning tree as a single switch port.
PAgP and LACP Modes
Table 29-1 shows the user-configurable EtherChannel modes for the channel-group interface configuration command. Switch interfaces exchange PAgP packets only with partner interfaces configured in the auto or desirable
modes. Switch interfaces exchange LACP packets only with partner
interfaces configured in the active or passive modes. Interfaces
configured in the on mode do not exchange PAgP or LACP packets.
Exchanging PAgP Packets
Both the auto and desirable
PAgP modes allow interfaces to negotiate with partner interfaces to
determine if they can form an EtherChannel based on criteria such as
interface speed and, for Layer 2 EtherChannels, trunking state and VLAN
numbers.
Interfaces can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. For example:
•An interface in the desirable mode can form an EtherChannel with another interface that is in the desirable or auto mode.
An interface in the desirable mode can form an EtherChannel with another interface that is in the desirable or auto mode.
•An interface in the auto mode can form an EtherChannel with another interface in the desirable mode.
An interface in the auto mode can form an EtherChannel with another interface in the desirable mode.
An interface in the auto mode cannot form an EtherChannel with another interface that is also in the auto mode because neither interface starts PAgP negotiation.
An interface in the on mode that is added to a port channel is forced to have the same characteristics as the already existing on mode interfaces in the channel.
If your switch is connected to a partner that is PAgP-capable, you can
configure the switch interface for nonsilent operation by using the non-silent keyword. If you do not specify non-silent with the auto or desirable mode, silent mode is assumed.
The silent mode is used when the switch is connected to a device that is
not PAgP-capable and seldom, if ever, sends packets. An example of a
silent partner is a file server or a packet analyzer that is not
generating traffic. In this case, running PAgP on a physical port
connected to a silent partner prevents that switch port from ever
becoming operational; however, the silent setting allows PAgP to
operate, to attach the interface to a channel group, and to use the
interface for transmission.
Note An Etherchannel cannot be configured in both the PAgP and LACP modes.
An Etherchannel cannot be configured in both the PAgP and LACP modes.
Exchanging LACP Packets
Both the active and passive LACP modes
allow interfaces to negotiate with partner interfaces to determine if
they can form an EtherChannel based on criteria such as interface speed
and, for Layer 2 EtherChannels, trunking state and VLAN numbers.
Interfaces can form an EtherChannel when they are in different LACP modes as long as the modes are compatible. For example:
•An interface in the active mode can form an EtherChannel with another interface that is in the active or passive mode.
An interface in the active mode can form an EtherChannel with another interface that is in the active or passive mode.
•An interface in the active mode can form an EtherChannel with another interface in the passive mode.
An interface in the active mode can form an EtherChannel with another interface in the passive mode.
An interface in the passive mode cannot form an EtherChannel with another interface that is also in the passive mode because neither interface starts LACP negotiation.
An interface in the on mode that is added to a port channel is forced to have the same characteristics as the already existing on mode interfaces in the channel.
Note An Etherchannel cannot be configured in both the PAgP and LACP modes.
An Etherchannel cannot be configured in both the PAgP and LACP modes.
Caution You should exercise care when setting the mode to on (manual configuration). All ports configured in the on
mode are bundled in the same group and are forced to have similar
characteristics. If the group is misconfigured, packet loss or
spanning-tree loops might occur.
You should exercise care when setting the mode to on (manual configuration). All ports configured in the on
mode are bundled in the same group and are forced to have similar
characteristics. If the group is misconfigured, packet loss or
spanning-tree loops might occur.
Physical Learners and Aggregate-Port Learners
Network devices are classified as PAgP physical learners or
aggregate-port learners. A device is a physical learner if it learns
addresses by physical ports and directs transmissions based on that
knowledge. A device is an aggregate-port learner if it learns addresses
by aggregate (logical) ports.
When a device and its partner are both aggregate-port learners, they
learn the address on the logical port-channel. The device sends packets
to the source by using any of the interfaces in the EtherChannel. With
aggregate-port learning, it is not important on which physical port the
packet arrives.
PAgP cannot automatically detect when the partner device is a physical
learner and the local device is an aggregate-port learner. Therefore,
you must manually set the learning method on the local device or
source-based distribution by using the pagp learn-method interface
configuration command. With source-based distribution, any given source
MAC address is always sent on the same physical port.
You can also configure a single interface within the group for all
transmissions and use other interfaces for hot standby. The unused
interfaces in the group can be swapped into operation in just a few
seconds if the selected single interface loses hardware-signal
detection. You can configure which interface is always selected for
packet transmission by changing its priority by using the pagp port-priority interface configuration command. The higher the priority, the more likely that the port will be selected.
PAgP and LACP Interaction with Other Features
The Dynamic Trunking Protocol (DTP) and Cisco Discovery Protocol (CDP)
send and receive packets over the physical interfaces in the
EtherChannel. Trunk ports send and receive PAgP and LACP protocol data
units (PDUs) on the lowest numbered VLAN.
Spanning tree sends packets over the first interface in the EtherChannel.
The MAC address of a Layer 3 EtherChannel is the MAC address of the first interface in the port-channel.
PAgP sends and receives PAgP PDUs only from interfaces that have PAgP
enabled for the auto or desirable mode. LACP sends and receives LACP
PDUs only from interfaces that have LACP enabled for the active or
passive mode.
Understanding Load Balancing and Forwarding Methods
EtherChannel balances the traffic load across the links in a channel by
randomly associating a newly-learned MAC address with one of the links
in the channel.
With source-MAC address forwarding, when packets are forwarded to an
EtherChannel, they are distributed across the ports in the channel based
on the source-MAC address of the incoming packet. Therefore, to provide
load balancing, packets from different hosts use different ports in the
channel, but packets from the same host use the same port in the
channel (and the MAC address learned by the switch does not change).
When source-MAC address forwarding is used, load distribution based on
the source and destination IP address is also enabled for routed IP
traffic. All routed IP traffic chooses a port based on the source and
destination IP address. Packets between two IP hosts always use the same
port in the channel, and traffic between any other pair of hosts can
use a different port in the channel.
With destination-MAC address forwarding, when packets are forwarded to
an EtherChannel, they are distributed across the ports in the channel
based on the destination host's MAC address of the incoming packet.
Therefore, packets to the same destination are forwarded over the same
port, and packets to a different destination are sent on a different
port in the channel. You configure the load balancing and forwarding
method by using the port-channel load-balance global configuration command.
In Figure 29-3,
multiple workstations are connected to a switch, and an EtherChannel
connects the switch to the router. Source-based load balancing is used
on the switch end of the EtherChannel to ensure that the switch
efficiently uses the bandwidth of the router by distributing traffic
from the workstation across the physical links. Since the router is a
single MAC address device, it uses destination-based load balancing to
efficiently spread the traffic to the workstations across the physical
links in the EtherChannel.
Use the option that provides the greatest variety in your configuration.
For example, if the traffic on a channel is going only to a single MAC
address, using the destination-MAC address always chooses the same link
in the channel; using source addresses or IP addresses might result in
better load balancing.
Figure 29-3 Load Distribution and Forwarding Methods
Configuring EtherChannels
These sections describe how to configure EtherChannel on Layer 2 and Layer 3 interfaces:
Note Make sure that the interfaces are correctly configured (see the "EtherChannel Configuration Guidelines" section).
Make sure that the interfaces are correctly configured (see the "EtherChannel Configuration Guidelines" section).
Note After
you configure an EtherChannel, configuration changes applied to the
port-channel interface apply to all the physical interfaces assigned to
the port-channel interface, and configuration changes applied to the
physical interface affect only the interface where you apply the
configuration.
After
you configure an EtherChannel, configuration changes applied to the
port-channel interface apply to all the physical interfaces assigned to
the port-channel interface, and configuration changes applied to the
physical interface affect only the interface where you apply the
configuration.
Default EtherChannel Configuration
Table 29-2 shows the default EtherChannel configuration.
EtherChannel Configuration Guidelines
If improperly configured, some EtherChannel interfaces are automatically
disabled to avoid network loops and other problems. Follow these
guidelines to avoid configuration problems:
•Configure an EtherChannel with up to eight Ethernet interfaces of the same type.
Configure an EtherChannel with up to eight Ethernet interfaces of the same type.
Note Do not configure a GigaStack GBIC port as part of an EtherChannel.
Do not configure a GigaStack GBIC port as part of an EtherChannel.
•Configure all interfaces in an EtherChannel to operate at the same speeds and duplex modes.
Configure all interfaces in an EtherChannel to operate at the same speeds and duplex modes.
•Enable all interfaces in an EtherChannel. An interface in an EtherChannel that is disabled by using the shutdown
interface configuration command is treated as a link failure, and its
traffic is transferred to one of the remaining interfaces in the
EtherChannel.
Enable all interfaces in an EtherChannel. An interface in an EtherChannel that is disabled by using the shutdown
interface configuration command is treated as a link failure, and its
traffic is transferred to one of the remaining interfaces in the
EtherChannel.
•When
a group is first created, all ports follow the parameters set for the
first port to be added to the group. If you change the configuration of
one of these parameters, you must also make the changes to all ports in
the group:
When
a group is first created, all ports follow the parameters set for the
first port to be added to the group. If you change the configuration of
one of these parameters, you must also make the changes to all ports in
the group:
–Allowed-VLAN list
Allowed-VLAN list
–Spanning-tree path cost for each VLAN
Spanning-tree path cost for each VLAN
–Spanning-tree port priority for each VLAN
Spanning-tree port priority for each VLAN
–Spanning-tree Port Fast setting
Spanning-tree Port Fast setting
•An
EtherChannel interface that is configured as a Switched Port Analyzer
(SPAN) destination port does not join the group until it is deconfigured
as a SPAN destination port.Do not configure a port that belongs to an
EtherChannel port group as a secure port.
An
EtherChannel interface that is configured as a Switched Port Analyzer
(SPAN) destination port does not join the group until it is deconfigured
as a SPAN destination port.Do not configure a port that belongs to an
EtherChannel port group as a secure port.
•Before
enabling 802.1X on the port, you must first remove it from the
EtherChannel. If you try to enable 802.1X on an EtherChannel or on an
active port in an EtherChannel, an error message appears, and 802.1X is
not enabled. If you enable 802.1X on a not-yet active port of an
EtherChannel, the port does not join the EtherChannel.
Before
enabling 802.1X on the port, you must first remove it from the
EtherChannel. If you try to enable 802.1X on an EtherChannel or on an
active port in an EtherChannel, an error message appears, and 802.1X is
not enabled. If you enable 802.1X on a not-yet active port of an
EtherChannel, the port does not join the EtherChannel.
•For Layer 2 EtherChannels:
For Layer 2 EtherChannels:
–Assign
all interfaces in the EtherChannel to the same VLAN, or configure them
as trunks. Interfaces with different native VLANs cannot form an
EtherChannel.
Assign
all interfaces in the EtherChannel to the same VLAN, or configure them
as trunks. Interfaces with different native VLANs cannot form an
EtherChannel.
–If
you configure an EtherChannel from trunk interfaces, verify that the
trunking mode (ISL or 802.1Q) is the same on all the trunks.
Inconsistent trunk modes on EtherChannel interfaces can have unexpected
results.
If
you configure an EtherChannel from trunk interfaces, verify that the
trunking mode (ISL or 802.1Q) is the same on all the trunks.
Inconsistent trunk modes on EtherChannel interfaces can have unexpected
results.
–An
EtherChannel supports the same allowed range of VLANs on all the
interfaces in a trunking Layer 2 EtherChannel. If the allowed range of
VLANs is not the same, the interfaces do not form an EtherChannel even
when PAgP is set to the auto or desirable mode.
An
EtherChannel supports the same allowed range of VLANs on all the
interfaces in a trunking Layer 2 EtherChannel. If the allowed range of
VLANs is not the same, the interfaces do not form an EtherChannel even
when PAgP is set to the auto or desirable mode.
–Interfaces
with different spanning-tree path costs can form an EtherChannel if
they are otherwise compatibly configured. Setting different
spanning-tree path costs does not, by itself, make interfaces
incompatible for the formation of an EtherChannel.
Interfaces
with different spanning-tree path costs can form an EtherChannel if
they are otherwise compatibly configured. Setting different
spanning-tree path costs does not, by itself, make interfaces
incompatible for the formation of an EtherChannel.
•For
Layer 3 EtherChannels, assign the Layer 3 address to the port-channel
logical interface, not to the physical interfaces in the channel.
For
Layer 3 EtherChannels, assign the Layer 3 address to the port-channel
logical interface, not to the physical interfaces in the channel.
Configuring Layer 2 EtherChannels
You configure Layer 2 EtherChannels by configuring the Ethernet interfaces with the channel-group
interface configuration command, which creates the port-channel logical
interface. You cannot put a Layer 2 interface into a manually created
port-channel interface.
Note Layer 2 interfaces must be connected and functioning for IOS to create port-channel interfaces.
Layer 2 interfaces must be connected and functioning for IOS to create port-channel interfaces.
Beginning in privileged EXEC mode, follow these steps to assign a Layer 2 Ethernet interface to a Layer 2 EtherChannel:
Command
|
Purpose
|
|
|---|---|---|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface interface-id
|
Enter interface configuration mode, and specify a physical interface to configure.
Valid interfaces include physical interfaces.
Up to eight interfaces of the same type and speed can be configured for the same group.
|
Step 3
|
switchport mode {access | trunk}
switchport access vlan vlan-id
|
Assign all interfaces as static-access ports in the same VLAN, or configure them as trunks.
If you configure the interface as a static-access port, assign it to only one VLAN. The range is 1 to 4094.
|
Step 4
|
channel-group channel-group-number mode
{{auto [non-silent] | desirable [non-silent] | on} | {active | passive}} |
Assign the interface to a channel group, and specify the PAgP or LACP mode.
For channel-group-number, the range is 1 to 64. Each EtherChannel can have up to eight compatibly configured Ethernet interfaces.
For mode, select one of these keywords:
•
active—Enables
LACP only if an LACP device is detected. It places an interface into an
active negotiating state, in which the interface starts negotiations
with other interfaces by sending LACP packets.
•
auto—Enables
PAgP only if a PAgP device is detected. It places an interface into a
passive negotiating state, in which the interface responds to PAgP
packets it receives but does not start PAgP packet negotiation.
•
desirable—Unconditionally
enables PAgP. It places an interface into an active negotiating state,
in which the interface starts negotiations with other interfaces by
sending PAgP packets.
•
on—Forces the interface to channel without PAgP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.
•
non-silent—If
your switch is connected to a partner that is PAgP-capable, you can
configure the switch interface for nonsilent operation. You can
configure an interface with the non-silent keyword for use with the auto or desirable mode. If you do not specify non-silent with the auto or desirable
mode, silent is assumed. The silent setting is for connections to file
servers or packet analyzers. This setting allows PAgP to operate, to
attach the interface to a channel group, and to use the interface for
transmission.
•
passive—Enables
LACP on an interface and places it into a passive negotiating state, in
which the interface responds to LACP packets that it receives, but does
not start LACP packet negotiation.
For information on compatible PAgP and LACP modes for the switch and its partner, see the "PAgP and LACP Modes" section.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show running-config
|
Verify your entries.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To remove an interface from the EtherChannel group, use the no channel-group interface configuration command.
This example shows how to assign Gigabit Ethernet interfaces 0/4 and 0/5
as static-access ports in VLAN 10 to channel 5 with the PAgP mode desirable:
Switch# configure terminal
Switch(config)# interface range gigabitethernet0/4 -5
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 10
Switch(config-if-range)# channel-group 5 mode desirable
Switch(config-if-range)# end
Configuring Layer 3 EtherChannels
To configure Layer 3 EtherChannels, you create the port-channel logical
interface and then put the Ethernet interfaces into the port-channel as
described in the next two sections.
Creating Port-Channel Logical Interfaces
When configuring Layer 3 EtherChannels, you must manually create the port-channel logical interface first by using the interface port-channel global configuration command. Then, you put the logical interface into the channel group by using the channel-group interface configuration command.
Note To
move an IP address from a physical interface to an EtherChannel, you
must delete the IP address from the physical interface before
configuring it on the port-channel interface.
To
move an IP address from a physical interface to an EtherChannel, you
must delete the IP address from the physical interface before
configuring it on the port-channel interface.
Beginning in privileged EXEC mode, follow these steps to create a port-channel interface for a Layer 3 EtherChannel:
Command
|
Purpose
|
|
|---|---|---|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface port-channel port-channel-number
|
Enter interface configuration mode, and create the port-channel logical interface.
For port-channel-number, the range is 1 to 64.
|
Step 3
|
no switchport
|
Put the interface into Layer 3 mode.
|
Step 4
|
ip address ip-address mask
|
Assign an IP address and subnet mask to the EtherChannel.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show etherchannel channel-group-number detail
|
Verify your entries.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
Step 8
|
Assign an Ethernet interface to the Layer 3 EtherChannel. For more information, see the "Configuring the Physical Interfaces" section.
|
To remove the port-channel, use the no interface port-channel port-channel-number global configuration command.
This example shows how to create the logical port channel (5) and assign 172.10.20.10 as its IP address:
Switch# configure terminal
Switch(config)# interface port-channel 5
Switch(config-if)# no switchport
Switch(config-if)# ip address 172.10.20.10 255.255.255.0
Switch(config-if)# end
Configuring the Physical Interfaces
Beginning in privileged EXEC mode, follow these steps to assign an Ethernet interface to a Layer 3 EtherChannel:
Command
|
Purpose
|
|
|---|---|---|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface interface-id
|
Enter interface configuration mode, and specify a physical interface to configure.
Valid interfaces include physical interfaces.
Up to eight interfaces of the same type and speed can be configured for the same group.
|
Step 3
|
no ip address
|
Ensure that there is no IP address assigned to the physical interface.
|
Step 4
|
channel-group channel-group-number mode {auto [non-silent] | desirable [non-silent] | on | active | passive }
|
Assign the interface to a channel group, and specify the PAgP or LACP mode.
For channel-group-number, the range is 1 to 64. This number must be the same as the port-channel-number (logical port) configured in the "Creating Port-Channel Logical Interfaces" section.
Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces.
For mode, select one of these keywords:
•
active—Enables
LACP only if an LACP device is detected. It places an interface into an
active negotiating state, in which the interface starts negotiations
with other interfaces by sending LACP packets.
•
auto—Enables
PAgP only if a PAgP device is detected. It places an interface into a
passive negotiating state, in which the interface responds to PAgP
packets it receives but does not start PAgP packet negotiation.
•
desirable—Unconditionally
enables PAgP. It places an interface into an active negotiating state,
in which the interface starts negotiations with other interfaces by
sending PAgP packets.
•
non-silent—If
your switch is connected to a partner that is PAgP capable, you can
configure the switch interface for nonsilent operation. You can
configure an interface with the non-silent keyword for use with the auto or desirable mode. If you do not specify non-silent with the auto or desirable
mode, silent is assumed. The silent setting is for connections to file
servers or packet analyzers; this setting allows PAgP to operate, to
attach the interface to a channel group, and to use the interface for
transmission.
•
on—Forces the interface to channel without PAgP or LACP. With the on mode, a usable EtherChannel exists only when an interface group in the on mode is connected to another interface group in the on mode.
•
passive—Enables
LACP on an interface and places it into a passive negotiating state, in
which the interface responds to LACP packets that it receives, but does
not start LACP packet negotiation.
For information on compatible PAgP modes for the switch and its partner, see the "PAgP and LACP Modes" section.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show running-config
|
Verify your entries.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To remove an interface from the EtherChannel group, use the no channel-group interface configuration command.
This example shows how to assign Gigabit Ethernet interfaces 0/4 and 0/5 to channel 5 with the PAgP mode desirable:
Switch# configure terminal
Switch(config)# interface range gigabitethernet0/4 -5
Switch(config-if-range)# no ip address
Switch(config-if-range)# channel-group 5 mode desirable
Switch(config-if-range)# end
Configuring EtherChannel Load Balancing
This section describes how to configure EtherChannel load balancing by
using source-based or destination-based forwarding methods. For more
information, see the "Understanding Load Balancing and Forwarding Methods" section.
Beginning in privileged EXEC mode, follow these steps to configure EtherChannel load balancing:
To return EtherChannel load balancing to the default configuration, use the no port-channel load-balance global configuration command.
Configuring the PAgP Learn Method and Priority
Network devices are classified as PAgP physical learners or
aggregate-port learners. A device is a physical learner if it learns
addresses by physical ports and directs transmissions based on that
knowledge. A device is an aggregate-port learner if it learns addresses
by aggregate ports.
For compatibility with Catalyst 1900 series switches, configure the PAgP
learning method on the Catalyst 3550 switches to learn source-MAC
addresses on the physical port. The switch then sends packets to the
Catalyst 1900 switch using the same interface in the EtherChannel from
which it learned the source address.
Note The Catalyst 3550 supports address learning only on aggregate ports even though the physical-port keyword is provided in the CLI. The pagp learn-method command and the pagp port-priority
command have no effect on the switch hardware, but they are required
for PAgP interoperability with devices that only support address
learning by physical ports, such as the Catalyst 1900 switch.
When the link partner to the Catalyst 3550 switch is a physical learner, we recommend that you configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command and to set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command. Use the pagp learn-method command only in this situation.
The Catalyst 3550 supports address learning only on aggregate ports even though the physical-port keyword is provided in the CLI. The pagp learn-method command and the pagp port-priority
command have no effect on the switch hardware, but they are required
for PAgP interoperability with devices that only support address
learning by physical ports, such as the Catalyst 1900 switch.When the link partner to the Catalyst 3550 switch is a physical learner, we recommend that you configure the switch as a physical-port learner by using the pagp learn-method physical-port interface configuration command and to set the load-distribution method based on the source MAC address by using the port-channel load-balance src-mac global configuration command. Use the pagp learn-method command only in this situation.
Beginning in privileged EXEC mode, follow these steps to configure your
switch as a PAgP physical-port learner and to adjust the priority so
that the same port in the bundle is selected for sending packets:
Command
|
Purpose
|
|
|---|---|---|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface interface-id
|
Enter interface configuration mode, and specify the interface for transmission.
|
Step 3
|
pagp learn-method physical-port
|
Select the PAgP learning method.
By default, aggregation-port
learning is selected, which means the switch sends packets to the
source by using any of the interfaces in the EtherChannel. With
aggregate-port learning, it is not important on which physical port the
packet arrives.
Select physical-port to connect with another switch that is a physical learner. Make sure to configure the port-channel load-balance global configuration command to src-mac as described in the "Configuring EtherChannel Load Balancing" section.
The learning method must be configured the same at both ends of the link.
|
Step 4
|
pagp port-priority priority
|
Assign a priority so that the selected interface is chosen for packet transmission.
For priority, the range is 0 to 255. The
default is 128. The higher the priority, the more likely that the
interface will be used for PAgP transmission.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show running-config
or
show pagp channel-group-number internal
|
Verify your entries.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To return the priority to its default setting, use the no pagp port-priority interface configuration command. To return the learning method to its default setting, use the no pagp learn-method interface configuration command.
Configuring the LACP Port Priority
You can set the priority for each port in an EtherChannel that is
configured for LACP by using the lacp port-priority privileged EXEC
command. The range is from 1 to 65535. Beginning in privileged EXEC
mode, follow these steps to configure the LACP port priority:
Configuring Hot Standby Ports
When enabled, LACP tries to configure the maximum number of
LACP-compatible ports in a channel, up to a maximum of 16 ports. Only
eight LACP links can be active at one time. Any additional links are put
in a hot standby state. If one of the active links becomes inactive, a
link that is in hot standby mode becomes active in its place.
If more than eight links are configured for an EtherChannel group, the
software determines which of the hot standby ports to make active based
on:
•LACP port-priority
LACP port-priority
•Port ID
Port ID
All ports default to the same port priority. You can change the port
priority of LACP EtherChannel ports to specify which hot standby links
become active first by using the lacp port-priority interface configuration command to set the port priority to a value lower than the default of 32768.
The hot standby ports that have lower port numbers become active in the
channel first unless the port priority is configured to be a lower
number than the default value of 32768.
Note If
LACP is not able to aggregate all the ports that are compatible (for
example, the remote system might have more restrictive hardware
limitations), all the ports that cannot be actively included in the
EtherChannel are put in hot standby state and are used only if one of
the channeled ports fails.
If
LACP is not able to aggregate all the ports that are compatible (for
example, the remote system might have more restrictive hardware
limitations), all the ports that cannot be actively included in the
EtherChannel are put in hot standby state and are used only if one of
the channeled ports fails.
Configuring the LACP System Priority
You can set the system priority for all of the EtherChannels that are
configured for LACP by using the lacp system-priority privileged EXEC
command. The range is from 1 to 65535.
Note The lacp system-priority command is global. You cannot set a system priority for each LACP-configured channel separately.
The lacp system-priority command is global. You cannot set a system priority for each LACP-configured channel separately.
We recommend using this command only when there are a combination of
LACP-configured EtherChannels that are in both active and standby modes.
Beginning in privileged EXEC mode, follow these steps to configure the LACP system priority:
Displaying EtherChannel, PAgP, and LACP Status
You can use the privileged EXEC commands described in Table 29-3Table 29-3Table 29-3 to display EtherChannel, PAgP, and LACP status information:
Command
|
Description
|
|---|---|
show etherchannel [channel-group-number] {brief | detail | load-balance | port | port-channel | summary}
|
Displays EtherChannel information in a brief, detailed, and one-line
summary form. Also displays the load-balance or frame-distribution
scheme, port, and port-channel information.
|
Displays PAgP information such as traffic information, the internal PAgP configuration, and neighbor information.
|
|
show lacp [channel-group-number] {counters | internal | neighbor}2
|
Displays LACP information such as traffic information, the internal PAgP configuration, and neighbor information.
|
1 You can clear PAgP channel-group information and traffic filters by using the clear pagp {channel-group-number [counters] | counters} privileged EXEC command.
2 You can clear LACP channel-group information and traffic filters by using the clear lacp {channel-group-number [counters] | counters} privileged EXEC command.
|
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