EtherChannel Question

NullCode

Hi.
Why does EtherChannel only support 8 ports ? ("An EtherChannel can be created from between two and eight active Fast Ethernet, Gigabit Ethernet or 10-Gigabit Ethernet ports, with an additional one to eight inactive (failover) ports which become active as the other active ports fail.")
Why not 16-20?

chmorin

Good question, but the why is not nearly as important at the what (in this case). Inside a Cisco switch the configurations will only let you do 8. Keep in mind that it is only per channel group. You could potentially have 64 etherchannels spread out through different channel groups.

tiersten

NullCode wrote: »

Hi.
Why does EtherChannel only support 8 ports ? ("An EtherChannel can be created from between two and eight active Fast Ethernet, Gigabit Ethernet or 10-Gigabit Ethernet ports, with an additional one to eight inactive (failover) ports which become active as the other active ports fail.")
Why not 16-20?

It is just how the load balancing algorithm used by EtherChannel works.

Why would you actually want more than 8 though? If you need more than 80Gbps then either you've got some really unusual configuration requirements or you need to design your network better. The number of ports on a switch isn't unlimited and using 20 ports for a single link is going to mean even with a chassis based switch you're going to be running low.

You'll get issues with oversubscription and having the EtherChannel split over cards anyway even if you could make a 20 link EtherChannel.

NullCode

Well maybe now, 80Gbps is enough, but i was wondering if there was a limitation of some sort(except of the "because it was made this way"), or a tehnical reason why only 8 ports.

tiersten

NullCode wrote: »

Well maybe now, 80Gbps is enough

You generally move up to the next generation Ethernet standard if 8xWhatever isn't enough. In this case it'd be 40Gbps or 100Gbps Ethernet which are both still draft standards.

The other option would be to buy a big chassis switch. The Nexus 7018 has a fabric capable of 230Gbps per slot and a total of 7.8Tbps over the entire chassis.

NullCode wrote: »

but i was wondering if there was a limitation of some sort(except of the "because it was made this way"), or a tehnical reason why only 8 ports.

The limit of 8 links for EtherChannel is a technical limitation due to the load balancing algorithm only supporting 8 active links. It is a design limitation however as to why they chose 8. They could have chosen 16 and it would have worked in a similar fashion.

jason_lunde

NullCode,
As Tiersten stated, it has to do with the cisco proprietary hashing algorithm, and how packets are load-balanced on the links. Their hashing algorithm will give a computed value from 0 to 7 (8 ). Based on how many links are configured, each link will accept "x" values. Note the chart at this link:
Understanding EtherChannel Load Balancing and Redundancy on Catalyst Switches - Cisco Systems

So using a cisco device, with cisco hashing algorithms, you can only utilize up to 8 links in the etherchannel, actively. That is why you can have some standby links, because when a link fails, another one will start carrying packets destined for that index (computed from the hash). hth's

Ahhh you beat me to the reply Tiersten!

tiersten

jason_lunde wrote: »

Ahhh you beat me to the reply Tiersten!

You've got the better reply that has links and technical information though

chmorin

NullCode wrote: »

Well maybe now, 80Gbps is enough, but i was wondering if there was a limitation of some sort(except of the "because it was made this way"), or a tehnical reason why only 8 ports.

If the need arises, I'm sure cisco will change their capabilities. If cisco kept its standards without upgrade we would still be using hubs and token rings.

NullCode

Thank you chmorin, tiersten and jason_lunde for your replies. It helped.
I got a better grasp at EtherChannel.
Thx.