EtherChannel

multiple host -- ASW1 -- DSW1

ASW = Access layer Switch, a switch that end hosts connect to DSW = Distribution layer switch, a switch that access layer switches connect to

When the bandwith of the interfaces connected to end hosts is greater than the bandwidth of the connection to the distribution switch(es), this is called oversubscription. Some oversubscription is acceptable, but too much will cause congestion.

if you connect two switchs together with multiple links, all except one will be disabled by spanning tree
if all of ASW1's interfaces were forwarding, Layer 2 loops would form between ASW1 and DSW1, leading to broadcast storms.
Other links will be unused unless the active link fails. in that case one of the inactive links will start forwarding
EtherChannel groups multiple interfaces together to act as a single interface.
STP will treat this group as a single interface

Traffic using the EtherChannel wil be load balanced among the physical interfaces in the group. An algorithm is used to determine which traffic will use which physical interface.

Some other names for an EtherChannel are:

Port Channel
LAG (Link aggregaton Group)

Load Balancing

EtherChannel load balances based on flows
A flow is a communication between two nodes in the network
Frames in the same flow will be forwarded using the same physicial interface.
If frames in the same flow were forwarded using different physical interfaces, some frames may arrive at the destination out of order, which can cause problems
You can change the inputs used in the interface selection calculation.
Inputs that can be used:
- Source MAC
- Destination MAC
- Source and Destination MAC
- Source IP
- Destination IP
- Source and Destination IP

Commands

see current configuration

ASW1#show etherchannel load-balance
### default will be set to src-dst-ip

for configuring load balance configuration

ASW1(config)#port-channel load-balance src-dst-mac

## to see other method
ASW1(config)#port-channel load-balance ?

EtherChannel Configuration

There are three methods of EtherChannel configuration on Cisco switches:

PAgP (Port Aggregation Protocol)
- Cisco proprietary protocol
- Dynamically negotiates the creation/maintenance of the EtherChannel. (like DTP does for trunks)
LACP (Link Aggregation Control Protocol)
- Industry standard protocol (IEEE 802.3ad)
- Dynamically negotiate the creation/maintenance of the EtherChannel. (like DTP does for trunks)
Static EtherChannel
- A protocol isn't used to determine if an EtherChannel should be formed.
- Interfaces are statically configured to form an EtherChannel

Up to 8 interfaces can be formed into a single EtherChannel (LACP allows up to 16, but only 8 will be active, the other 8 will be in standby mode, waiting for an active interface to fail)

ASW1(config)#inteface range g0/0 - 3
## to see all methods
ASW1(config-if-range)#channel-group 1 mode ?
## for PAgP
ASW1(config-if-range)#channel-group 1 mode desirable

note: The channel-group number has to match for member interfaces on the same switch.
However, it doesn't have to match the channel-group number on the other switch.
(channel-group 1 on ASW1 can form an EhterChannel with channel-group 2 on DSW1)

Member intefaces must have matching configurations.

Same duplex (full/half)
Same speed
Same switchport mode (access/trunk)
Same allowed VLANs/native VLAN (for trunk interfaces)

If an interface's configurations do not match the others, it will be excluded from the EtherChannel

to see running configuration of the EtherChannel

ASW1#show etherchannel summary
## less utilise command
ASW1#show etherchannel port-channel

Layer 3 EtherChannel

ASW1(config)#int range g0/0 - 3
ASW1(config-if-range)#no switchport
ASW1(config-if-range)#channel-group 1 mode active


ASW1(config-if-range)#int po1
ASW1(config-if)#ip address 10.0.0.1 255.255.255.252

Review

What is EtherChannel? what problems does it solve?
Configuring Layer 2/Layer 3 EtherChannel

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