Which option is valid for EtherChannel load balancing?
A. source MAC address and source IP address
B. destination MAC address and destination IP address
C. source MAC address and destination IP address
D. source MAC address and destination MAC address
D is actual answer as no load balancing method is having combination of MAC and IP among any of the six methods. they are either MAC or IP based. only option “D” is having MAC for source and destination.
you may issue a cmd on a sw to check
config t
port-channel load-balance ?
there are six options, and the only correct ans is D
The correct answer is A.
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750e_3560e/software/release/12-2_55_se/configuration/guide/3750escg/swethchl.pdf
LOOK AT PAGE 38-8/38-9
Souce MAC is load balancing.
“With source-MAC address forwarding, when packets are forwarded to an EtherChannel, they are
distributed across the ports in the channel based on the source-MAC address of the incoming packet.
Therefore, to provide load-balancing, packets from different hosts use different ports in the channel, but
packets from the same host use the same port in the channel.”
The IP side of things are a little bit trickier. So, i’ll put both paragraphs from the PDF:
With source-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are
distributed across the ports in the EtherChannel based on the source-IP address of the incoming packet.
Therefore, to provide load-balancing, packets from different IP addresses use different ports in the
channel, but packets from the same IP address use the same port in the channel.
With destination-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are
distributed across the ports in the EtherChannel based on the destination-IP address of the incoming
packet. Therefore, to provide load-balancing, packets from the same IP source address sent to different
IP destination addresses could be sent on different ports in the channel. But packets sent from different
source IP addresses to the same destination IP address are always sent on the same port in the channel.
If you look at the very LAST sentence from destination IP, you see that it isn’t load balancing for one device.
Think of a switch connected to a windows server with 8 connections to it. It will run LACP or Ether-Channel ON, obviously. PAgP is Cisco Proprietary, and most servers used won’t be Cisco.
So, with that server connected to the switch we have two options for IP, Source-IP and Dest-IP.
Source IP:
This means that each flow of traffic from an IP (think of one on the internet) will have a round-robin (by default) using ALL the links if there are 8+flows of IP traffic.
So, on the server, if you have Chrome opened with 8 different tabs opened to 8 different websites, the EtherChannel will use at least all 8 links(could be more for administrative uses).
Destination IP:
When a switch puts traffic destined for the EtherChannel, It will look at what the destination IP is and use one available link to send traffic to that device.
So, if we follow the same example as above, if we have 8 links to a server, if the server only has one NIC, then ALL IP traffic will only use ONE link in the EtherChannel.
Thus, “A” is the correct answer.