Etherchannels Flashcards
What are etherchannels?
Logical bundlings of two to eight links between two switches.
How does STP view etherchannels?
As a single port, no matter how many links make up the etherchannel.
In STP, how is the port cost of an etherchannel determined?
By the number and speed of the ports in the etherchannel. More, faster ports=lower port cost.
What action does STP take when a single port in an etherchannel goes down?
It increases the port cost for the etherchannel.
Does the channel group number have to match between two switches?
No. It’s a local value.
What are the three variations of etherchannel?
LACP, PAgP, and static.
What is a port channel?
The logical representation of an etherchannel. It’s how etherchannels are referred to within CIOS syntax.
What command is used to configure a port channel?
From interface config: channel-group (#) mode ( )
What is PAgP?
Port aggregation protocol. A Cisco proprietary etherchannel negotiation protocol.
What is LACP?
Link aggregation control protocol. Industry standard etherchannel negotiation protocol.
What is a good show command to check the overall status of etherchannels on a switch?
Show etherchannel brief, or Show etherchannel summary.
What does LACP use port priority for?
To determine which 8 of the total 16 allowed ports will be actively used in the etherchannel. Lower priority ports will be used.
What is a good command to check etherchannel relationship status?
Show LACP/PAgP neighbor.
How many ports can be assigned to a LACP etherchannel?
16, but only 8 will be used, determined by priority.
What are the LACP port modes?
Active and passive.
What are the PAgP port modes?
Auto and desirable.
What happens if you make a change to an individual PAgP port?
The change will be made on all ports in the etherchannel.
What criteria can be chosen for etherchannel load-distribution?
Source MAC, destination MAC, source & destination MAC, source IP, destination IP, source & destination IP, TCP/UDP source, TCP/UDP destination, TCP/UPD source & destination.
Can load-distribution criteria be chosen on an etherchannel-by-etherchannel basis?
No, it can only be configured globally.
How does etherchannel load-distribution work?
Values 0-7 are assigned equally among the etherchannel interfaces. Unique MAC/IPs (whatever you’re using for criteria) are mapped to these values, and in turn are assigned to an interface. This is NOT true load-balancing.
How is etherchannel load-balancing different when using source & destination MAC/IP?
The XOR (exclusive-or) operation is used to map each unique combination of addresses to a port. This operation compares the last few bits of the source and destination address to determine it’s value, which is then mapped to a port.
Describe STP etherchannel misconfig guard.
STP etherchannel misconfig guard protects against loops caused by statically configured etherchannels that are not configured on both switches. If a misconfiguration is detected, the switch will be placed into err-disable state.
What command will change the etherchannel load-distribution criteria?
From global config, “port-channel load-balance ___”
What command will enable STP etherchannel misconfig guard?
From global config, “spanning etherchannel guard misconfig”
Which etherchannel protocol supports half duplex?
PAgP
Do portchannel commands overwrite individual port commands?
Not always. It’s best practice to keep configurations for the port channel.
What must all ports in a layer 2 etherchannel agree on?
Speed, duplex, mapped VLANs, native VLAN, trunking protocol.
What must ports in a layer 3 etherchannel agree on?
No switch port, speed and duplex.
