Etherchannel/port-channel


  • Etherchannel/port-channel
  • On different Cisco switches it is possible to create logical connections that
  • are made-up off different fysical interface. It is needed that these interface
  • do have the same speed.
  • Each channel must be made up of min 2, max 8 interfaces.
  • The best is to use 2 ,4 or 8 interfaces. This will give the perfect load-balancing.
  • The load-balancing can be bases on layer 2/3 or 4 information.
  • It is not possible to have different load-balancing methods for different Etherchannels
  • on one switch. If the load-balancing method is change, it is applicable for all.
  • The load-balancing method can be:
  • –          src-mac
  • –          dst-mac
  • –          src-dst-mac
  • –          src-ip
  • –          dst-ip
  • –          src-dst-ip
  • –          src-port
  • –          dst-port
  • –          src-dst-port
  • By using <port-channel load-balance {option}> it is possible to change to method.
  • If a single header is used to load-balance the low-order bits is used to dictate to
  • witch interface the frame is send. If two headers are used a XOR function is used on
  • the low-order bits.
  • It is possible to change what path with-in the etherchannel a frame takes by used the following command:
  • <test etherchannel load-balance interface port-channel [#] ip [src] [dst]>
  • to assign a physical interface towards a port-channel use the following command:
  • channel-group [#] mode on
  • There are two type of dynamic protocols to negotiate an etherchannels: PAgP and LACP 8021.AD
  • PAgP is Cisco proprietary
  • When these protocols start to communicate there is an exchange of information before the port-channel can be formed. The following items must match before a port-channel can form:
  • –          same speed/duplex
  • –          Access VLAN (if not trunked)
  • –          Same trunking type, allowed VLAN and native VLAN (if trunked)
  • –          Each port must have the same STP cost per VLAN with-in the portchannel
  • –          No SPAN ports
  • channel-group [#] mode on (disables PAgP en LACP)
  • channel-group [#] mode off (disables PAgP en LACP and prevent the ports to form a port-channel)
  • channel-group [#] mode auto (use PAgP in a passive mode, it will wait until a PAgP packet will be send)
  • channel-group [#] mode passive (use LACP in a passive mode, it will wait until a PAgP packet will be send)
  • channel-group [#] mode desirable (use PAgP in an active mode, it will start to send  PAgP packets)
  • channel-group [#] mode active (use LACP in an active mode, it will start to send  LACP packets)
  • 3750(config)#interface range gigabitethernet 1/0/2 - 4
  • 3750(config-if-range)#channel-group 1 mode on
  • 3750(config-if-range)#switchport
  • 3750(config-if-range)#switchport trunk encapsulation dot1q
  • 3750(config-if-range)#switchport mode trunk
  • First type the channel-group command. After that all interface commands will be automatically duplicated on all the interfaces group in the channel-group.
  •  
  • With LACP it is possible to create a port-channel on a stack (3560/3750 switches).
  • This is based on IOS version 12.2(25)SEE
  • Show command’s
  • show interfaces port-channel [channel-group-number]
  • show etherchannel [channel-group-number] summary
  • Verify command’s
  • test etherchannel load-balance interface port-channel [#] ip [src] [dst