Configuring LACP & PAGP
LACP & PAGP:
Link Aggregation Control Protocol and Port Aggregation Protocol both sounds same but the gap between these protocols is LACP is Open standard and can be used on any supported Product, where as PAGP is Cisco's proprietary and can be configured only in the Cisco devices.
What are these these protocols?
Generally we use trunk links to enable communication between two switches (for inter-vlan routing) when we use a single port for the trunk link (e.g., Gig port ) it gives us throughput of 1 Gbps, Making few more ports as trunk causes a loop and STP will block it from farming
Configuring the LACP or PAGP gives us the capability to add multiple trunk links to a switch, without causing loops. So that providing more throughput.
Port-Channel:
When we have bundled multiple interfaces into a trunk group, A new logical interface is created automatically and its called as Port-Channel. When we configure this port channel interface the configuration will be applied to all the physical interfaces associated in it.
For example: consider there is a server behing a switch, so many hits are coming for that server then a single trunk link can't facilitate the desired output. So by configuring LACP we are giving the switch to get the data from multiple links, there by serving the demand, reducing the load.
Configuration:
There are a total of 5 modes available in configuring these protocols:
Active
Passive
Auto
Desirable
On
Active & Passive modes are for Lacp and Auto & Desirable modes are for PAgP.
For LACP, If one side we configure Active in the other end we need to configure passive, and vice versa
For PAgP, If one side we configure Desirable in the other end we need to configure Auto. and vice versa
When we configure Active at one end it will unconditionally creates the port channel and device cofigured with passive will negotiate with it.
And
When we configure Desirable it will unconditionally creates a Port channel and the Device configured Auto will negotiate with it.
where as If we configured ON at both ends it will unconditionally enables port channel on both switches, this is not recommended because sometimes protocol mismatches causes the link down.
Configuration commands:
on Switch-1
config term
int range fa 0/1-4
channel-protocol lacp
channel-group 1 mode active
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan all
on Switch-2:
configure term
int range fa 0/1-4
channel-protocol lacp
channel-group 1 mode passive
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan all
You can verify the configuration by following commands on both ends:
show etherchannel
show etherchannel summary
show etherchannel details
you will find a port channle in your interfaces check it with
show running-config
show ip interfaces brief
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