GigaStack GBIC not supported for IPT applications???

[kkudlacek]

I'm hearing from a colleague that the copper GigaStack GBICs are not supported (by Cisco) for IPT applications, even if configured in full-duplex mode (a single cable between two switches). Is this true? Seems hard to believe...

Kale Kudlacek

CCNP,CCDA, Cisco Wireless SE,FE

Dimension Data

kale.kudlacek@us.didata.com

[gary.shaw]

You can only stack 2 switches together with the Gigastack and maintain QoS. If you add a third (daisy chaining) it cannot support QoS correctly and you could have problems, its probably ok in a lab, but dont put it out in a production environment.

[kkudlacek]

Thanks for the reply.

What if you were to use a 3550-12G switch and "star" connect 3 3524's into it using two Gigastack GBIC's per switch connection back to the 3550-12G? Each Gigastack GBIC would connect using a single copper cable in this scenerio... Seems like that would work fine.

More to the point, does Cisco actually have a policy of not supporting GigaStack GBIC (copper) modules with IPT under *any* circumstance?

Thanks!

-Kale

[electro22]

GigaStacking multiple switches together leads to a shared bandwidth scenario. Basically the GigaStack ports act as a hub.

The way around this is to use a 3508. That is an 8 port gigaStack device, each switch has a pt to pt connection to the 3508 instead of sharing bandwidth among all the switches.

This scenario with the 3508 can preserve QoS.

-Jaret

[Tom Dillon]

My understanding of the problem is using both ports on a single GigaStack GBIC. Once you use both ports connecting three switches the GigaStack can only operate in half duplex, which is the problem.

However, what we have tested and have in production, is GigaStack GBICs to stack more than two switches by only using one port on each GigaStack GBIC. In other words, use the GigaStack GBIC just as you would a SX GBIC.

As long as you do not use both ports on the GigaStack, the connection will be full duplex. We still use SX GBICs when we connect the stack to our Cat6500, but we use GigaStack for the inner switches in the stack.

I am not advocating stacking Cat3524s, but GigaStack GBICs can be deployed without compromising your QoS because of a half duplex connection.