129 lines
4.1 KiB
Markdown
129 lines
4.1 KiB
Markdown
---
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id: 23. EtherChannel
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aliases: []
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tags: []
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---
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# EtherChannel
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multiple host -- ASW1 -- DSW1
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ASW = Access layer Switch, a switch that end hosts connect to
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DSW = Distribution layer switch, a switch that access layer switches connect to
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When the bandwith of the interfaces connected to end hosts is greater than the bandwidth of the
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connection to the distribution switch(es), this is called *oversubscription*.
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Some oversubscription is acceptable, but too much will cause congestion.
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- if you connect two switchs together with multiple links, all except one will be disabled by
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[[spanning tree]]
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- if all of ASW1's interfaces were forwarding, Layer 2 loops would form between ASW1 and DSW1,
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leading to [[broadcast storms]].
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- Other links will be unused unless the active link fails. in that case one of the inactive
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links will start forwarding
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- EtherChannel groups multiple interfaces together to act as a single interface.
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- STP will treat this group as a single interface
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Traffic using the EtherChannel wil be load balanced among the physical interfaces in the group.
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An [[algorithm]] is used to determine which traffic will use which physical interface.
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Some other names for an EtherChannel are:
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- Port Channel
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- LAG (Link aggregaton Group)
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## Load Balancing
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- EtherChannel load balances based on flows
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- A flow is a communication between two nodes in the network
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- Frames in the same flow will be forwarded using the same physicial interface.
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- If frames in the same flow were forwarded using different physical interfaces, some frames
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may arrive at the destination out of order, which can cause problems
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- You can change the inputs used in the interface selection calculation.
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- Inputs that can be used:
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- Source [[MAC]]
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- Destination MAC
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- Source and Destination MAC
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- Source [[IP]]
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- Destination IP
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- Source and Destination IP
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### Commands
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see current configuration
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```Cisco
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ASW1#show etherchannel load-balance
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### default will be set to src-dst-ip
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```
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for configuring load balance configuration
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```Cisco
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ASW1(config)#port-channel load-balance src-dst-mac
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## to see other method
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ASW1(config)#port-channel load-balance ?
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```
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## EtherChannel Configuration
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There are three methods of EtherChannel configuration on Cisco switches:
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- PAgP (Port Aggregation Protocol)
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- Cisco proprietary protocol
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- Dynamically negotiates the creation/maintenance of the EtherChannel.
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(like DTP does for trunks)
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- LACP (Link Aggregation Control Protocol)
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- Industry standard protocol (IEEE 802.3ad)
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- Dynamically negotiate the creation/maintenance of the EtherChannel.
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(like DTP does for trunks)
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- Static EtherChannel
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- A protocol isn't used to determine if an EtherChannel should be formed.
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- Interfaces are statically configured to form an EtherChannel
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Up to *8 interfaces* can be formed into a single EtherChannel (LACP allows up to 16, but only
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8 will be active, the other 8 will be in standby mode, waiting for an active interface to fail)
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```Cisco
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ASW1(config)#inteface range g0/0 - 3
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## to see all methods
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ASW1(config-if-range)#channel-group 1 mode ?
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## for PAgP
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ASW1(config-if-range)#channel-group 1 mode desirable
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```
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note: The channel-group number has to match for member interfaces on the same switch.
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However, it doesn't have to match the channel-group number on the other switch.
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(channel-group 1 on ASW1 can form an EhterChannel with channel-group 2 on DSW1)
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Member intefaces must have matching configurations.
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- Same duplex (full/half)
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- Same speed
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- Same switchport mode (access/trunk)
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- Same allowed VLANs/native VLAN (for trunk interfaces)
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If an interface's configurations do not match the others, it will be excluded from the EtherChannel
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to see running configuration of the EtherChannel
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```Cisco
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ASW1#show etherchannel summary
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## less utilise command
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ASW1#show etherchannel port-channel
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```
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## Layer 3 EtherChannel
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```Cisco
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ASW1(config)#int range g0/0 - 3
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ASW1(config-if-range)#no switchport
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ASW1(config-if-range)#channel-group 1 mode active
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ASW1(config-if-range)#int po1
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ASW1(config-if)#ip address 10.0.0.1 255.255.255.252
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```
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## Review
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- What is EtherChannel? what problems does it solve?
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- Configuring Layer 2/Layer 3 EtherChannel
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