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100MbTrunk vs. 1gig link

Mohamed Hamedi
Respected Contributor

100MbTrunk vs. 1gig link

Can someone clarify for me which is better; a single gig link, or say ten 100Mb trunk?
Taking redundancy out, what are the other benefits of using a trunk in this scenario?

4 REPLIES
Kell van Daal
Respected Contributor

Re: 100MbTrunk vs. 1gig link

In most cases a single gig link will be preferable.
A trunk can consist of up to 8 links, making a trunk having a maximum of 800Mb, which is obviously less then 1Gb.
Also because load balancing is done based on SA/DA pairs, it is possible that the 800Mb trunk won't be used fully. Some links in the trunk may be saturated, while others are almost unused.
Even more, it is never possible to get a speed above 100Mb for a single traffic flow, because all traffic from one flow will allways be assigned to the same link.
Also troubleshooting performance issues can be easier with only one link compared to trunks.

The biggest advantage of trunks above single links is indeed the "built-in" redudancy, but since you said not to consider this, I would recommend using a single gig link, or the best of two worlds, a gig trunk consisting of two or more links.
Les Ligetfalvy
Esteemed Contributor

Re: 100MbTrunk vs. 1gig link

Let me use the transportation system as an example.

You have a train going from point A to Point B. The train travels at 100 miles per hour. You add addition tracks so that two trains can travel at the same time but they still travel at the same speed. You don't get there any quicker.

Take the airplane... it travels at over 600 miles per hour.
asdf_44
Occasional Advisor

Re: 100MbTrunk vs. 1gig link

You also need to consider how the traffic is sent across the trunk ports. If you have a host (connected to a gig link) sending at line rate to a 4-port gig port trunk, then there's a chance that all that traffic will get sent to the same trunk port. (This will happen if the host is sending traffic to a single host.)

If an additional host tries to send traffic across that 4-port trunk and happens to chose the same link as the other host, we now lose traffic.
Les Ligetfalvy
Esteemed Contributor

Re: 100MbTrunk vs. 1gig link

>If an additional host tries to send traffic across that 4-port trunk and happens to chose the same link as the other host, we now lose traffic.

I'm sorry, assuming the trunks are ISL, the host does not get to choose the trunk member. That decision is left to the switch.