EtherChannel
Under normal conditions, all but one redundant physical link between two switches will be disabled by STP at one end.Port aggregation allows multiple physical ports to be bundled together to form a single logical port. The switch and STP will treat the bundled ports as a single interface, eliminating the possibility of a switching loop. Cisco’s implementation of port aggregation is called EtherChannel. EtherChannel supports Fast, Gigabit, and 10 Gigabit Ethernet ports. A maximum of 8 active ports are supported in a single EtherChannel. If the ports are operating in full duplex, the maximum
theoretical bandwidth:
• Fast Ethernet – 1600 Mbps
• Gigabit Ethernet – 16 Gbps
• 10 Gigabit Ethernet – 160 Gbps
The maximum number of supported EtherChannels on a single switch is platform-dependent, though most support up to 64 or 128 EtherChannels.
For an EtherChannel to become active, all ports in the bundle must be
EtherChannel Negotiation
proprietary protocol unless you have a specific need for it (such as ancient hardware). That
leaves LACP and "on", both of which have a specific benefit.
EtherChannel will only be formed after successful negotiation between its two ends. However, this negotiation introduces an overhead and delay in initialization. Statically configuring an EtherChannel ("on") imposes no delay yet can cause serious problems if not properly configured at both ends. To configure an EtherChannel using LACP negotiation, each side must be set to either active or passive; only interfaces configured in active mode will attempt to negotiate an EtherChannel. Passive interfaces merely respond to LACP requests. PAgP behaves the same, but its two modes are refered to as desirable and auto.
EtherChannel Load-Balancing
EtherChannel is Cisco's term for bundling two or more physical Ethernet links for the purposes of aggregating available bandwidth and, to a lesser extent, providing a measure of physical
EtherChannel Requirements
configured identically, regardless if the EtherChannel is being used with
access or trunk ports. Port settings that must be identical include the
following:
• Speed settings
• Duplex settings
• STP settings
• VLAN membership (for access ports)
• Native VLAN (for trunk ports)
• Allowed VLANs (for trunk ports)
• Trunking encapsulation protocol (for trunk ports)
On trunk connections, the above settings must be configured identically
across all participating ports on both switches.Historically, port-security has not been supported on an EtherChannel. Newer platforms may provide support as long as port-security is enabled onboth the physical interfaces and the EtherChannel itself.
An EtherChannel can be established using one of three mechanisms:
· PAgP - Cisco's proprietary negotiation protocol
· LACP (IEEE 802.3ad) - Standards-based negotiation protocol
· Static Persistence ("On") - No negotiation protocol is used
Any of these three mechanisms will suffice for most scenarios, however the choice does deserve
LACP helps protect against switching loops caused by misconfiguration; when enabled, an
Only a single line is needed to configure a group of ports as an EtherChannel:
As noted, a virtual port-channel interface Port-channel1 has been created to represent the logical link.
Switchport configurations applied to this interface are replicated to the physical member interfaces. We can
inspect the health of the EtherChannel with the
show etherchannel summary command:
The opposite side of the LACP EtherChannel will typically be configured as passive, however it can be
active as well.
Almost a full three seconds elapsed between the member ports transitioning to the up state and the port-
channel interface coming up. Once it did, we can see the state of the EtherChannel has changed to "in use":
Traffic sent across an EtherChannel is not evenly distributed across all ports
in the bundle. Instead, EtherChannel utilizes a load-balancing algorithm to
determine the port to send the traffic out, based on one of several criteria:
• Source IP address - src-ip
• Destination IP address - dst-ip
• Source and destination IP address - src-dst-ip
• Source MAC address - src-mac
• Destination MAC address - dst-mac
• Source and Destination MAC address - src-dst-mac
• Source TCP/UDP port number - src-port
• Destination TCP/UDP port number - dst-port
• Source and destination port number - src-dst-port
Using a deterministic algorithm prevents perfect load-balancing. However, a
particular traffic flow is forced to always use the same port in the bundle,
preventing out-of-order delivery.
The default load-balancing method for a Layer-2 EtherChannel is either srcmac
or src-dst-mac, depending on the platform. The default method for a
Layer-3 EtherChannel is src-dst-ip.
The load-balancing method must be configured globally on the switch:
Switch(config)# port-channel load-balance src-dst-mac
To display the currently configured load-balancing method:
Switch# show etherchannel load-balance
EtherChannel Load-balancing Configuration:
src-dst-mac
To view the load on each port in an EtherChannel (output abbreviated):
Switch# show etherchannel 1 port-channel
Index Load Port EC state
------+------+--------+------------
0 55 Gi2/23 active
1 3A Gi2/24 active
The load is rather cryptically represented in a hexadecimal value.
Recall that a maximum of 8 active ports are supported in a single
EtherChannel. LACP supports adding an additional 8 ports into the bundle
in a standby state, to replace an active port if it goes down.
LACP assigns a numerical port-priority to each port, to determine which
ports become active in the EtherChannel. By default, the priority is set to
32768, and a lower priority is preferred. If there is a tie in port-priority, the
lowest port number is preferred.
To change the LACP port-priority to something other than default:
Switch(config)# interface range gi2/23 – 24
Switch(config-if)# lacp port-priority 100
LACP also assigns a system-priority to each switch, dictated which switch
becomes the decision-maker if there is a conflict about active ports. The
default system-priority is 32768, and a lower priority is again preferred. If
there is a tie in system-priority, the lowest switch MAC address is preferred.
To globally change the system-priority on a switch:
Switch(config)# lacp system-priority 500
Troubleshooting EtherChannel
To view status information on all configured EtherChannels:
Switch# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
R - Layer3 S - Layer2
U - port-channel in use
Group Port-channel Ports
---------- --------------- ---------------
1 Po1(SU) Gi2/23(P) Gi2/24(P)
Note that both ports have a status of P, which indicates that they are up and
active in the EtherChannel.
On Cisco Nexus switches, the syntax for this command is slightly different:
NexusSwitch# show port-channel summary
in the bundle. Instead, EtherChannel utilizes a load-balancing algorithm to
determine the port to send the traffic out, based on one of several criteria:
• Source IP address - src-ip
• Destination IP address - dst-ip
• Source and destination IP address - src-dst-ip
• Source MAC address - src-mac
• Destination MAC address - dst-mac
• Source and Destination MAC address - src-dst-mac
• Source TCP/UDP port number - src-port
• Destination TCP/UDP port number - dst-port
• Source and destination port number - src-dst-port
Using a deterministic algorithm prevents perfect load-balancing. However, a
particular traffic flow is forced to always use the same port in the bundle,
preventing out-of-order delivery.
The default load-balancing method for a Layer-2 EtherChannel is either srcmac
or src-dst-mac, depending on the platform. The default method for a
Layer-3 EtherChannel is src-dst-ip.
The load-balancing method must be configured globally on the switch:
Switch(config)# port-channel load-balance src-dst-mac
To display the currently configured load-balancing method:
Switch# show etherchannel load-balance
EtherChannel Load-balancing Configuration:
src-dst-mac
To view the load on each port in an EtherChannel (output abbreviated):
Switch# show etherchannel 1 port-channel
Index Load Port EC state
------+------+--------+------------
0 55 Gi2/23 active
1 3A Gi2/24 active
The load is rather cryptically represented in a hexadecimal value.
Recall that a maximum of 8 active ports are supported in a single
EtherChannel. LACP supports adding an additional 8 ports into the bundle
in a standby state, to replace an active port if it goes down.
LACP assigns a numerical port-priority to each port, to determine which
ports become active in the EtherChannel. By default, the priority is set to
32768, and a lower priority is preferred. If there is a tie in port-priority, the
lowest port number is preferred.
To change the LACP port-priority to something other than default:
Switch(config)# interface range gi2/23 – 24
Switch(config-if)# lacp port-priority 100
LACP also assigns a system-priority to each switch, dictated which switch
becomes the decision-maker if there is a conflict about active ports. The
default system-priority is 32768, and a lower priority is again preferred. If
there is a tie in system-priority, the lowest switch MAC address is preferred.
To globally change the system-priority on a switch:
Switch(config)# lacp system-priority 500
Troubleshooting EtherChannel
To view status information on all configured EtherChannels:
Switch# show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
R - Layer3 S - Layer2
U - port-channel in use
Group Port-channel Ports
---------- --------------- ---------------
1 Po1(SU) Gi2/23(P) Gi2/24(P)
Note that both ports have a status of P, which indicates that they are up and
active in the EtherChannel.
On Cisco Nexus switches, the syntax for this command is slightly different:
NexusSwitch# show port-channel summary
BASIC LAB ON ETHER-CHANNEL :
----SW0 configuration ----------
sw0(config-if-range)#int range fa0/1 - 2
sw0(config-if-range)#channel-protocol lacp
sw0(config-if-range)#channel-group 1 mode active
sw0(config-if-range)#int range fa0/3 - 4
sw0(config-if-range)#channel-protocol lacp
sw0(config-if-range)#channel-group 3 mode active
----SW2 configuration ----------
SW2(config-if-range)#int rang fa0/3 - 4
SW2(config-if-range)#channel-protocol lacp
SW2(config-if-range)#channel-group 3 mode active
SW2(config-if-range)#int range fa0/1 - 2
SW2(config-if-range)#channel-protocol lacp
SW2(config-if-range)#channel-group 2 mode active
----SW1 configuration ----------
sw1(config-if-range)#int range fa0/3 - 4
sw1(config-if-range)#channel-protocol lacp
sw1(config-if-range)#channel-group 2 mode active
sw1(config-if-range)#int range fa0/1 - 2
sw1(config-if-range)#channel-protocol lacp
sw1(config-if-range)#channel-group 1 mode active
----output after making ether-channel
sw0#sh etherchannel
Channel-group listing:
----------------------
Group: 1
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
Group: 3
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
SW2#sh etherchannel
Channel-group listing:
----------------------
Group: 2
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
Group: 3
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
sw1#sh etherchannel
Channel-group listing:
----------------------
Group: 1
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
Group: 2
----------
Group state = L2
Ports: 2 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
sw0# sh ip int brief
-- output cut---
Vlan1 unassigned YES unset administratively down down
Port-channel 1 unassigned YES unset up up
Port-channel 3 unassigned YES unset up up
PORT-CHANNEL
output shows that on sw0 port-channel1 and port-channel3 has been created and we can
assing ip addressing on this port-channel interface .
Only thing we have to take care into this that we have to make these swichports
as routable instead of switchport.
For making switch port routable we fire command " no swichport"
as you can see down in the command line.
sw0#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Also we can provide ip address to the logi
sw0(config)#int p1
sw0(config-if)#ip add 10.1.1.1 255.255.255.0 --- error
^
sw0(config-if)#no switchport
%LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel 1, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel 1, changed state to up
sw0(config-if)#ip add 10.1.1.1 255.255.255.0
sw0(config-if)#no sh
sw0(config-if)#end
sw0#
%SYS-5-CONFIG_I: Configured from console by console
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