Etherchannel

Etherchannel

Allows several physical links to be bundle together into a virtual port channel interface.We can pass traffic at the same time  in both links without spanning-tree shut  down one of those links.

From the point of view of Spanning-tree protocol it see etherchannel as a single bundle, a single interface..It wont block any of the links because it appears as One connection, One logical link

Benefits of etherchannel

1. Creates redundant-links 
2. Allows higher bandwidth between the switches 
3. provides load-balancing

 Although this sounds wonderful and it is there are some things to keep in mind. EtherChannel does not always distribute the traffic equally across all available links it depends on the number of links you have connected but even that does not always guarantee equal traffic.

  Etherchannel can look at the following methods to decide which physical link to send data over.

• The source MAC address
• The destination MAC address
• The source and destination MAC address
• The source IP address
• The destination IP address
• The source and destination IP address
• The source port
• The destination port
• The source and destination port

All of these methods depend on the hardware and software you are running but they will put a value between 0-7 on each connected link. Remember each link can have more than one value assigned to it.

• You need to configure both switches for the same connection mode: Link Aggregation Control Protocol (LACP), Port Aggregation Protocol (PAgP), or EtherChannel.
• PAgP is a Cisco propriety protocol, whereas LACP is an open standard. If you are creating EtherChannel with switches from other vendors, you need to use LACP.
  
  

  •  These protocols are made to negotiate  etherchannel between a couple of catalyst switches
  •  All ports in a channel group must have the same configuration for Speed and Duplex settings; otherwise, you have anarchy on your hands
  • All ports must be assigned to the same VLAN and have matching switchport modes.
  •  When STP needs to send data out, it uses only one of the configured ports, instead of sending the data over all the ports.
  •  

   PAGP

  
  

  

  LACP

  
  

  

  
  

  

  
  
  
  Layer 2 Etherchannel

  
  

  A connection  make up of a logical grouping of ports into a virtual interface that is configurable as a layer 2 interface
  
  
  A lot of Cisco cat switches support MDIX. An MDIX (for MDI crossover) is a version of MDI that enables connection between like devices. MDI ports connect to MDIX ports via straight-through twisted pair cabling; both MDI-to-MDI and MDIX-to-MDIX connections use crossover twisted pair cabling.
  
   Automatic medium-dependent interface crossover (auto-MDIX) is enabled by default. When you enable auto-MDIX, you must also set the interface speed and duplex to auto so that the feature operates correctly.
  
  You will understand these concepts much better after doing the next lab.
  
  

   

  
  

   Etherchannel Configuration

  
  
  We will use our current physical  switches instead of any emulation:
  

  

  
  
  We will use our current topology
  

  

  
  We will do some configuration so I will post it so you can copy and paste what I am doing.. :
  
  We will configure first fa0/9 & 10, speed and duplex auto so it can activate mdix.We choose channel group 20  out of the blue that is significant locally only ( doesn't need to be in the rest of the switches) , we will use Pagp in desirable mode on Switch A
  
  conf t
  int range fa0/9-10
  speed auto
  duplex auto
  mdix auto
  channel-group 20 mode ?
  channel-group 20 mode desirable
  exit
  int port-channel 20
  switchport trunk encapsulation dot1q
  switchport mode trunk
  end
  

  

  
  Now will check our current configuration
  
  
  

  

  
  
  We see that port 20 is created on Switch A..With int fa0/9 and fa0/10.Port is down   ( We haven't configure switch C yet : no connection )
  
  Now let's go to Switch C.
  
  The difference will be that channel group will be 30 and mode auto 
  

  
  

  Verification commands

  
  when we do the command show ip int brief   see what we got..
  

  

  
  
  
  it's up..
  
  
  
  
  

  

  
  We could see the ether-channel speed and the vlan on port-channel 30 that we just created.
  
    Two more important command:
  
  
  

  

  
  We could see here that port-channel 30 is in use and is layer 2.
  
  We  just verify that this exercise was successful!