Switching Commands Cisco

EtherChannel

Configuring link aggregation with LACP, PAgP, and static methods for bandwidth and redundancy

Bundle multiple physical links into a single logical link for increased bandwidth and redundancy.

Step 1: Create the port-channel interface Configure the logical port-channel interface with desired settings that will be inherited by member interfaces.

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SW1>enable
SW1#configure terminal
SW1(config)#interface port-channel 1
SW1(config-if)#description Link to SW2
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport trunk allowed vlan 10,20,30
SW1(config-if)#exit

Step 2: Add physical interfaces to the channel Configure the physical interfaces with identical settings and assign them to the port-channel group using LACP active mode.

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SW1(config)#interface range gigabitEthernet 0/1-2
SW1(config-if-range)#description Member of Po1
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#switchport trunk allowed vlan 10,20,30
SW1(config-if-range)#channel-protocol lacp
SW1(config-if-range)#channel-group 1 mode active
SW1(config-if-range)#no shutdown
SW1(config-if-range)#exit

Step 3: Configure load balancing method Set the load balancing method to distribute traffic based on source and destination IP addresses.

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SW1(config)#port-channel load-balance src-dst-ip
SW1(config)#end

Step 4: Configure the remote switch (SW2) Repeat the same configuration on the remote switch for the EtherChannel to form properly.

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SW2>enable
SW2#configure terminal
SW2(config)#interface port-channel 1
SW2(config-if)#description Link to SW1
SW2(config-if)#switchport mode trunk
SW2(config-if)#switchport trunk allowed vlan 10,20,30
SW2(config-if)#exit
SW2(config)#interface range gigabitEthernet 0/1-2
SW2(config-if-range)#switchport mode trunk
SW2(config-if-range)#switchport trunk allowed vlan 10,20,30
SW2(config-if-range)#channel-protocol lacp
SW2(config-if-range)#channel-group 1 mode active
SW2(config-if-range)#no shutdown
SW2(config-if-range)#end

Step 5: Verify the configuration

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SW1#show etherchannel summary
SW1#show etherchannel port-channel
SW1#show interfaces port-channel 1
SW1#show lacp neighbor

Key Points:

  • All member interfaces must have identical configurations (speed, duplex, VLAN settings)
  • Use LACP active mode on both sides for dynamic negotiation
  • Look for (P) flag in show etherchannel summary indicating ports are bundled
  • Channel will not form if there’s any configuration mismatch between members
  • Alternative modes: mode on (static), mode passive (LACP passive)

Static EtherChannel

Bundle multiple physical links into a single logical link without using negotiation protocols like LACP or PAgP.

Step 1: Create the port-channel interface Configure the logical port-channel interface that will represent the bundled links.

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SW1>enable
SW1#configure terminal
SW1(config)#interface port-channel 2
SW1(config-if)#description Static Link to SW2
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport trunk allowed vlan 10,20,30
SW1(config-if)#exit

Step 2: Add physical interfaces to the channel Configure physical interfaces with identical settings and assign them to the port-channel group using static mode.

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SW1(config)#interface range gigabitEthernet 0/3-4
SW1(config-if-range)#description Member of Po2
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#switchport trunk allowed vlan 10,20,30
SW1(config-if-range)#channel-group 2 mode on
SW1(config-if-range)#no shutdown
SW1(config-if-range)#exit

Step 3: Configure the remote switch (SW2) Repeat the same static configuration on the remote switch for the EtherChannel to function properly.

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SW2>enable
SW2#configure terminal
SW2(config)#interface port-channel 2
SW2(config-if)#description Static Link to SW1
SW2(config-if)#switchport mode trunk
SW2(config-if)#switchport trunk allowed vlan 10,20,30
SW2(config-if)#exit
SW2(config)#interface range gigabitEthernet 0/3-4
SW2(config-if-range)#switchport mode trunk
SW2(config-if-range)#switchport trunk allowed vlan 10,20,30
SW2(config-if-range)#channel-group 2 mode on
SW2(config-if-range)#no shutdown
SW2(config-if-range)#end

Step 4: Configure load balancing method (optional) Set how traffic is distributed across the member links.

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SW1(config)#port-channel load-balance src-dst-mac
SW1(config)#end

Step 5: Verify the configuration

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SW1#show etherchannel summary
SW1#show etherchannel port-channel
SW1#show interfaces port-channel 2
SW1#show running-config interface port-channel 2

Key Points:

  • Static EtherChannel uses mode on - no negotiation protocols
  • Both sides must use mode on for static channels to work
  • All member interfaces must have identical configurations
  • Look for (P) flag in show etherchannel summary indicating bundled ports
  • No fallback if misconfigured - links may go into err-disabled state
  • Less flexible than LACP but simpler configuration

Dynamic Etherchannel

Dynamic EtherChannel with PAgP

Configure EtherChannel using Cisco’s proprietary Port Aggregation Protocol (PAgP) for automatic link bundling negotiation.

Step 1: Create the port-channel interface Configure the logical port-channel interface that will represent the bundled links.

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SW1>enable
SW1#configure terminal
SW1(config)#interface port-channel 3
SW1(config-if)#description PAgP Link to SW2
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport trunk allowed vlan 10,20,30
SW1(config-if)#exit

Step 2: Configure physical interfaces with PAgP Set up the physical interfaces to use PAgP for dynamic negotiation. Use desirable mode to actively negotiate.

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SW1(config)#interface range gigabitEthernet 0/5-6
SW1(config-if-range)#description Member of Po3
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#switchport trunk allowed vlan 10,20,30
SW1(config-if-range)#channel-protocol pagp
SW1(config-if-range)#channel-group 3 mode desirable
SW1(config-if-range)#no shutdown
SW1(config-if-range)#exit

Step 3: Configure the remote switch (SW2) Configure the remote switch to participate in PAgP negotiation using auto mode.

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SW2>enable
SW2#configure terminal
SW2(config)#interface port-channel 3
SW2(config-if)#description PAgP Link to SW1
SW2(config-if)#switchport mode trunk
SW2(config-if)#switchport trunk allowed vlan 10,20,30
SW2(config-if)#exit
SW2(config)#interface range gigabitEthernet 0/5-6
SW2(config-if-range)#switchport mode trunk
SW2(config-if-range)#switchport trunk allowed vlan 10,20,30
SW2(config-if-range)#channel-protocol pagp
SW2(config-if-range)#channel-group 3 mode auto
SW2(config-if-range)#no shutdown
SW2(config-if-range)#end

Step 4: Configure load balancing method Set the traffic distribution method across the bundled links.

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SW1(config)#port-channel load-balance src-dst-port
SW1(config)#end

Step 5: Verify the configuration

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SW1#show etherchannel summary
SW1#show pagp neighbor
SW1#show pagp counters
SW1#show interfaces port-channel 3

Key Points:

  • PAgP is Cisco proprietary - only works between Cisco devices
  • desirable mode actively initiates negotiation
  • auto mode responds to negotiation but doesn’t initiate
  • At least one side must be in desirable mode for channel to form
  • Look for (P) flag in summary showing successful bundling
  • PAgP modes: desirable (active), auto (passive)