Chapter 7 - Layer 2 Port Aggregation Flashcards
What does LACP stand for?
Link Aggregation Control Protocol - IEEE 802.3ad
What etherchannel negotiation protocol follows an IEEE standard?
LACP - Link Aggregation Control Protocol
What etherchannel negotiation protocol is Cisco proprietary?
PAgP - Port Aggregation Protocol
What does PAgP stand for?
Port Aggregation Protocol
What modes does LACP operate in?
Active: Enable LACP unconditionally. (Sends LACP requests)
Passive: Enable LACP only if an LACP device is detected. (Waits for LACP requests and responds to requests for LACP negotiation).
Remember Passive - Passive links will NOT form an Etherchannel
What modes does PAgP operate in?
Desirable / Auto
Remember Auto - Auto links will not form an Etherchannel
Which 4 factors must be identical on interface members in an Etherchannel for them to function properly?
- Same speed and duplex
- Same mode (access or trunk)
- Same native and allowed VLANs on trunk ports
- Same access VLAN on access ports
How does STP path cost affect Etherchannel formation?
Interfaces with different STP port path costs can form an EtherChannel as long they are otherwise compatibly configured (speed / duplex / trunk settings / access vlan). Setting different STP port path costs does not, by itself, make interfaces incompatible for the formation of an EtherChannel.
How do you setup an etherchannel?
The configuration is done in interface configuration mode, several interfaces can be added at the same time using the interface range command.
(config-if-range)# channel-group 1 mode active
- this is for LACP
How do you check status of Etherchannel
! check Etherchannel members / status
show etherchannel summary
! Check etherchannel load balacing method
show etherchannel load-balance
Can you change an EtherChannel load balance method for a single portchannel?
No. Load balance methods are applied globally to the entire switch. It is not possible to have different load-balancing methods for different EtherChannels on one switch. If the load-balancing method is changed, it is applied to all EtherChannels.
In addition to source, destination, ip, and mac-address load balancing methods, what additional ways can Catalyst 4500 and 6500 switches load balance traffic on an Etherchannel?
src-port - Source port number
dst-port - Destination port number
src-dst-port - Source and destination port number
These switches can load balance on TCP and UDP ports (essentially by application)
Why is it reccomended to use even number of member links in an Etherchannel?
If you use four links, the algorithm will look at the last 2 bits. 2 bits mean four indexes: 00, 01, 10, and 11. Each link in the bundle will get assigned one of these indexes. If you bundle only three links, the algorithm will still need to use 2 bits to make decisions. One of the three links in the bundle will be utilized more than other two. With four links, the algorithm will strive to load-balance traffic in a 1:1:1:1 ratio. With three links, the algorithm will strive to load-balance traffic in a 2:1:1 ratio.
How can you check if EtherChanel Guard is configured?
It is actually a function of Spanning Tree and is enabled by default. # show spanning-tree summary
If it somehow got turned off it can be re-enabled by using the command:
spanning-tree etherchannel guard misconfig
How do you change the load balancing method on an EtherChannel?
This one is tricky. Remember to use the “port-channel” command from global config mode:
Switch(config)# port-channel load-balance
