Etherchannel is aggregation of redundant links.
Etherchannel makes use of the 3 links blocked by spanning-tree by aggregating all four links into 1 logical link. Etherchannel can do that for upto 8 ports! (if you have a 6500 switch).Advantages:
(1) Uses all links to maximize bandwidth.
(2)Load-balances over all 3 links.
(3)Uses automatic fail-over (if 1 link fails, it becomes a 3Gbps link, in this case).
(4)Simplifies logical interface configuration - Just configure 1 interface and the rest (3 in this case) will follow.
Two negotiation protocols:
(1) Port Aggregation Protocol (PAGP)
-Cisco Proprietary (first to come out)
-Port modes: auto, desirable, on
-Port modes: auto, desirable, on
-When a port is set to 'auto' it will automatically tune itself to whatever the connected port is set to. Auto-Auto on both sides won't make it an etherchannel because both sides are waiting for one side to be a desirable connection. Auto-Desirable thus would work however the best bet, and my personal preference is to set both sides to 'on' thus hardcoding the trunk and disabling this whole 'negotiation' game.
PAGP is more of a legacy protocol now.
PAGP is more of a legacy protocol now.
(2) Link Aggregation Control Protocol (LACP)
-Industry Standard (802.3AD)
-Port modes: passive, active, on
In the next post, we'll move on to configuring Etherchannel...-Port modes: passive, active, on
-passive = auto and active = desirable. Just different words, function is exactly the same.
LACP is more common and widely used due to it being industry-standard.
2 flavours of Etherchannel:
(1) Layer 2 Etherchannel: (For layer 2 switches such as 2950's.) is a simple bundling of multiple physical interfaces into a single logical port. That logical port acts and feels like a normal switchport except that it has a lot more bandwidth than a single switchport, and does load-balancing on those links, so basically it's something seen on a layer 2 domain.
(2) Layer 3 Etherchannel: (For layer 3 switches such as 3550 or above) means we could take all of the switchports and bundle them at layer 2 (which is where they all link up) but then assign them to a logical layer interface called a Port-Channel interface. That port-channel interface can be assigned an ip-address, it can ping, it's just like a routed port.
Common to see L3 Etherchannel configured between the distribution and core layer of the network.
LACP is more common and widely used due to it being industry-standard.
2 flavours of Etherchannel:
(1) Layer 2 Etherchannel: (For layer 2 switches such as 2950's.) is a simple bundling of multiple physical interfaces into a single logical port. That logical port acts and feels like a normal switchport except that it has a lot more bandwidth than a single switchport, and does load-balancing on those links, so basically it's something seen on a layer 2 domain.
(2) Layer 3 Etherchannel: (For layer 3 switches such as 3550 or above) means we could take all of the switchports and bundle them at layer 2 (which is where they all link up) but then assign them to a logical layer interface called a Port-Channel interface. That port-channel interface can be assigned an ip-address, it can ping, it's just like a routed port.
Common to see L3 Etherchannel configured between the distribution and core layer of the network.
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