when do you do load balancing?

CCIE_2011

I'm a the youngest guy here with my team. Some times i find things that are really not necessary, as number of vlans in the network ... etc.

However, couple of days ago i ask a Question in CCNP forum and got the perfect answer THANKS you all .... But another question came to my mind, this question is more CCDP question so it is better to ask the question here


Question :

Assume you have an access layer switch with two uplinks. If each uplink is sufficient to handle and pass all user traffic. will you go for "load balancing"?

Also you want to assure minimum down time if an uplink fails.

I will use in this switch Flex Link technology. which will re-converge in a less than 50 ms. which is much faster than re-converge of routed ports.


I know the question is quite big and it is not just easy to answer. well just want some hint to go and search my self


thanks in advance.

GT-Rob

Well, if you have the 2 links already, you could set up etherchannel and double your bandwidth. Otherwise, STP is going to block one of the ports.


STP with uplinkfast enabled will converge pretty quick. Probably faster than most would notice. The 2 links are probably there for high redundancy more than bandwidth. (and copper is cheap )

bighornsheep

CCIE_2011 wrote:

Assume you have an access layer switch with two uplinks. If each uplink is sufficient to handle and pass all user traffic. will you go for "load balancing"?

Depends on how you've designed your campus network, 2 uplinks to 2 different switches? Or the same switch? Are you terminating L2 traffic at the access or forming dot1q/ISL trunks to switch in one layer up?

GT-Rob wrote:

...you could set up etherchannel and double your bandwidth.

Only if the uplinks are connecting to the same switch, but this may or may not be the case.

GT-Rob wrote:

The 2 links are probably there for high redundancy more than bandwidth. (and copper is cheap )

Uplinks could be fiber too! And they are well.....not so cheap especially if you need to buy TwigGig converter, and the SFP and then realize your existing fiber infrastructure is SC, so then you have to buy SC-LC dongles.....

Back to the 2 uplink question, if the L2 traffic trunk from the access switch like in the case of a collapsed core for example, I think running MST would be a good idea and your topology allows for it. You could pass half of your VLANs through one trunk and the rest through the other, map those VLANs to instances, and your switches will treat it as though there's only 2 STP running. If a link fails, well MST incorporates RSTP, so you enjoy fast convergence as well!

ilcram19-2

etherchannel will give you load balancing doesnt exactlly double your bandwitdh, but etherchannel will give you both redundancy and fault tolerance.

if one of the links goes down stp doesnt have to go thrue all the recalculation again since one of the links still up

tech-airman

GT-Rob wrote:

Well, if you have the 2 links already, you could set up etherchannel and double your bandwidth. Otherwise, STP is going to block one of the ports.

GT-Rob,

The traditional "..2 links.." for an Access layer switch to Distribution layer devices, the first link goes to Distribution switch #1 and the second link goes to Distribution switch #2. So since those two links go to two separate switches, it will be difficult to "...set up etherchannel..."

tech-airman

CCIE_2011 wrote:

I'm a the youngest guy here with my team. Some times i find things that are really not necessary, as number of vlans in the network ... etc.

However, couple of days ago i ask a Question in CCNP forum and got the perfect answer THANKS you all .... But another question came to my mind, this question is more CCDP question so it is better to ask the question here


Question :

Assume you have an access layer switch with two uplinks. If each uplink is sufficient to handle and pass all user traffic. will you go for "load balancing"?

Also you want to assure minimum down time if an uplink fails.

I will use in this switch Flex Link technology. which will re-converge in a less than 50 ms. which is much faster than re-converge of routed ports.


I know the question is quite big and it is not just easy to answer. well just want some hint to go and search my self


thanks in advance.

CCIE_2011,

When you mention "...two uplinks..." how many upstream networking devices is that one access layer switch connected to?

1. 1 upstream networking device
2. 2 upstream networking devices

Paul Boz

Are you referring to load balancing two links to one uplink switch or one link to two different switches? If it's the former it's probably not worth it because it doesn't protect you from platform failure. If it's the latter then by all means do it. Redundancy in the network is never bad. Running an etherchannel (load balancing two or more links between two switches) is primarily useful when one link isn't enough bandwidth and you don't have the option to increase the bandwidth (no gig/10gig ports). You don't have a bandwidth problem per your post so it would be of minimal benefit.