ajout Etherchannel

23. EtherChannel.md

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+---
+id: 23. EtherChannel
+aliases: []
+tags: []
+---
+
+# 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
+```Cisco
+ASW1#show etherchannel load-balance
+### default will be set to src-dst-ip
+```
+
+for configuring load balance configuration
+```Cisco
+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)
+
+```Cisco
+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
+
+```Cisco
+ASW1#show etherchannel summary
+## less utilise command
+ASW1#show etherchannel port-channel
+```
+
+## Layer 3 EtherChannel
+
+```Cisco
+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