CCNA and CCNP candidates are well versed in Spanning-Tree Protocol, and one of the things about STP is the fact that it works nicely with very minimal or no extra settings. There’s one situation where STP works against us a little while it prevents switching loops, and that is the circumstance where two switches have multiple physical alterations.
You would believe that if you’ve got two physical connections between two switches, double as much information could be transmitted from one switch to another than if there was just one connection. STP does not allow this by default, but in an effort to avoid switching loops from forming, one of the avenues will be obstructed.
SW1 and SW2 are quick 0/12 and connected on ports fast0/11, via two different physical connections. Just interface 0/11 is traffic Since we can see here in SW1. STP has put another port into blocking mode (BLK).
SW1#show spanning vlan 10
(some output removed for clarity)
Interface Role Sts Cost Prio.Nbr Type
Fa0/11 Root FWD 19 128.11 P2p
Fa0/12 Altn BLK 19 128.12 P2p
STP is also hurting us by preventing us from using a valid route between SW1 and SW2 while STP is helping us by preventing switching loops. We can double the bandwidth available between both switches if we can use that route that is currently being obstructed.
An Etherchannel is being configured by the key to using the path. An Etherchannel is simply a logical bundling of two – 8 connections between two Cisco switches.
Configuring an Etherchannel is quite simple. Use the command”channel-group 1 mode on” on every port that you wish to be set into the Etherchannel. Of course, this must be performed on either switches should you put in an Etherchannel and do not do this on the ports on the switch that is opposite, the line protocol stay there and may probably go down.
An Etherchannel’s attractiveness is that STP sees the Etherchannel as a single link. STP does not observe that, if any of the physical connections within the Etherchannel go down, and STP won’t recalculate. The delay in transmission caused by an STP recalculation is prevented while traffic stream between the 2 switches will be slowed. An Etherchannel also allows us to work with multiple physical connections at one time.
Here’s the Way to place these ports into an Etherchannel:
SW1#conf t
Enter configuration commands, one per line. Finish with CNTL/Z.
SW1(config)#interface fast 0/11
SW1(config-if)#channel-group 1 mode on
Developing a port-channel port Port-channel 1
SW1(config-if)#interface fast 0/12
SW1(config-if)#channel-group 1 mode on
SW2#conf t
Enter configuration commands, one per line. Finish with CNTL/Z.
SW2(config)#int fast 0/11
SW2(config-if)#channel-group 1 mode on
SW2(config-if)#int fast 0/12
SW2(config-if)#channel-group 1 mode on
The command”show interface trunk” and”display spanning-tree vlan 10″ is employed to check the Etherchannel configuration.
SW2#show interface trunk (some output removed for clarity)
Port Mode Encapsulation Status Native vlan
Po1 desired 802.1q trunking 1
SW2#show spanning vlan 10 (some output removed for clarity)
Interface Role Sts Cost Prio.Nbr Type
Po1 Desg FWD 12 128.65 P2p
We saw vents here before configuring the Etherchannel. We view”Po1″, which stands for the port”port-channel1″. Here is actually the logical interface created when an Etherchannel is assembled. We’re now utilizing both paths between the 2 switches at one time!
That’s one benefit in action let’s see yet another. Normally, if the only open route between 2 trunking switches goes down, is a significant delay while another legitimate route is opened – close to a moment in some scenarios. We will now shut down port 0/11 on SW2 and realize the influence.
SW2#conf t
Enter configuration commands, one per line. Finish with CNTL/Z.
SW2(config)#int fast 0/11
SW2(config-if)#shutdown
3w0d: percent LINK-5-CHANGED: Interface FastEthernet0/11, altered
state to administratively down
SW2#show spanning vlan 10
VLAN0010
Spanning tree enabled protocol ieee
Interface Role Sts Cost Prio.Nbr Type
Po1 Desg FWD 19 128.65 P2p
SW2#show interface backward
Port Mode Encapsulation Status Native vlan
Po1 desired 802.1q trunking 1
The Etherchannel didn’t go down! The Etherchannel is seen by STP as one link therefore, as far as STP is concerned, just happened.
Assembling an Etherchannel and understanding how it can benefit your network is an essential ability for CCNA and CCNP achievement, as it comes in helpful on the work also. Ensure that you are comfortable before choosing the exams of Cisco with constructing a single!
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