EtherChannel
Layer2 and Layer3 Ether Channels, L2 grouping of switched ports and L3 is a grouping of routed ports acting as a single port with a single IP address
Last updated
Layer2 and Layer3 Ether Channels, L2 grouping of switched ports and L3 is a grouping of routed ports acting as a single port with a single IP address
Last updated
Traffic using the EtherChannel will load balance among the physical interfaces in the group. An algorithm is used to determine which traffic will use which physical interface and is based on 'flows' which is basically means "communication between 2 nodes in the network" (say between a PC and a Printer) Frames in the SAME flow will be forwarded using the SAME PHYSICAL interface (if frames in the same flow were forwarded using different interfaces, some frames sould arrive at the destination out or order, causing problems.Some applications could handle that but others could not) To determine which interface is used for the particular 'flow' is based on configurable inputs:
Source OR Destination MAC address
Source OR Destination IP address
Source AND Destination MAC address
Source AND Destination IP address
(Some switches also use L4 inputs such as TCP and UDP ports)
Port Channel
LAG (Link Aggregation Group)
Load Balancing - Check
From above we can see that the load balancing is using the "Source AND Destination IP" algorithm. This means that lets sy all traffic from 10.1.1.1 going to destination 10.1.1.20 will ALWAYS use a specific physical interface within the EtherChannel
Load Balancing - Adjust Settings
SW1# show etherchannel load-balance
SW1(config)# port-channel load-balance <method>
There are 3 methods:
PAgP (Port Aggregation Protocol) - this is Cisco's proprietary protocol. Only can be done between 2 or more Cisco switches. Dynamically negotiates the creation/maintenance of the EtherChannel (like DTP for trunks)
LACP (Link Aggregation Protocol) - Industry Standard (IEEE 802.3ad)- Also dynamically negotiates the creation and maintenance of the EtherChannel. This is the preferred protocol to use especially across vendor switches.
Static EtherChannel - hard-coded and not recommended as a protocol is not used to determine if an EtherChannel should be formed. Interfaces statically configured to form and EtherChannel
Up to 8 interfaces can be configured into an EtherChannel (LACP allows up to 16 but only 8 will be active, the other 8 in standby mode waiting for an active interface to fail)
The configuration for each is almost identical - just have to change out some keywords
NOTE !! CHANNEL-GROUP command is used to configure the etherchannel but the name of the VIRTUAL interface that is CREATED, is "Port-channel" as seen above The "channel-group 1" number has to MATCH the member interfaces (gi0/0 - 3) BUT does NOT have to match the channel-group number on the other switch (eg, channel-group1 on SW1 CAN form am etherchannel with channel-group 33 on DWS1 !!!
Exactly the same, just change the "mode" from whatever it was to "ON"
ASW1(config)# interface port-channel 1
ASW1(config-if) switchport trunk encapsulation dot1q
ASW1(config-if) switchport mode trunk
ASW1(config-if) do show interfaces trunk
We will do the same on Switch3 (LACP currently not enabled) and then check the status of the EtherChannel
VERIFY COMMANDS:
SW2#show etherchannel summary SW2#show etherchannel port-channel
OK - now we can see that EtherChannel is working we can now configure the individual ports as (in this case) trunk ports.
Have replaces ASW1 and DSW1 with multilayer switches. Instead of a Layer 2 connection between them use a lawyer 3 connection. Modern network design often leans towards using L3 connections between switches, because that way SPANNING TREE wont be an issue anywhere in the network!! We could have 4 switches interconnected in a mesh, and if we are connecting them with Layer 3 routed ports, all interfaces will be up and forwarding, none will have to be disabled due to Spanning Tree
If we look at the smaller diagram, even though the 4 etherchannels are L2 thay can cause L2 broadcast storms ansd so Spanning Tree will block one of these to STOP L2 loops
