The last article was about the layer 3 switches and how they can be useful in your network. Today I introduce another technology that was introduced in CCNA. Suppose I have a button that connects to the server with 1 Gbps link. Now suppose two servers want to exchange data at very high speed but was unable to because the limit on the carrying capacity. What if I know the switch to make (at least) two links connected to behave as one? Inter-server communication can be performed at 2 Gbps now, utilizing both links. Or suppose we have a switch that connects to the upstream switch. To provide redundancy we require two links will be connected so that if one link fails switch can automatically failover to another link. If you are trying to connect two cables to the simple switch, one of them will get blocked because of the STP and will not be used (the loop is being formed) .To try and solve this problem a technology called link aggregation / bundling / bond was created. Before each major vendor has its own specific protocol, but now has changed. IEEE has come up with a standard known as IEEE 802.1ax LACP (link control protocol aggregation) to an Ethernet network. Please note that this technology can be used ONLY for ethernet networks. Because it is open source protocol can be used on a variety of devices from different vendors, including HP, Juniper and Cisco course. these days even servers can be configured to run LACP (thorough treatment of how to run LACP on a server in a future article). Referring to the diagram below which we are trying to implement in fewer article.
As you can clearly see the two links between Switch 0 and multilayer switch 2 are both active, indicated by a green light. This is because they act as a collection of single link. STP and infact all devices see this as an interface known as port-channel interface. To ensure a smooth link aggregate formation steps are recommended.
- Both the ports on the switch should be of the same type.
- Similarly, one port of a switch should be connected to a similar port on the other switch. This means that their hardware properties, link speed, duplex mode, IOS version etc must be the same.
- Any configuration after link aggregation should be done on the newly formed aggregate itnerface.
These steps should ensure that you have a robust aggregate pipe of multiple links. The number of links that can be aggregated depends on the switch being used.
Implementation of aggregate link
On switch 0:
enable //we will define port channel bundle with id 1
conf t
interface range fa0/1-2 //change the itnerface number according to your needs
channel-group 1 mode active //define a bundle of two links with LACP set
channel-protocol lacp //ensure LACP is working
interface port-channel 1 //the logical aggregate interface
switchport mode trunk encapsulation dot1q //required
switchport mode trunk
On switch 1:
enable //we will define port channel bundle with id 2
conf t
interface range fa0/23-24
channel-group 2 mode active
channel-protocol lacp
interface port-channel 2
switchport mode trunk encapsulation dot1q //required
switchport mode trunk
On multilayer switch:
en
conf t
interface port-channel 1
switchport mode trunk encapsulation dot1q //required
switchport mode trunk
en
conf t
interface port-channel 2
switchport mode trunk encapsulation dot1q //required
switchport mode trunk
The above diagram clearly exhibits that none of the ports were blocked even though in a normal configuration they would have.
Who would have thought that it was so easy to make multiple ports on your switch to behave as one giving far superior throughput and network redundancy at the same time! Note that a device can have upto 16 ports bundled together. So if all the ports have a capacity of 1gbps, that is 16gbps of pipe in your network!
This was a quick rundown of what Ethernet bonding/aggregation is . In the next article in this series gre tunneling will be introduced which is also another interesting topic in CCNP curriculum.
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