QOS and Half-Duplex GigaStack Cascade Configuration

[sslater04]

Does anyone know if Stacking more then two switches together using the Half-Duplex GigaStack Cascade Configuration causes an issue with the QoS in a VoIp environment. If so can you point me to some documentation?

[Aaron Harrison · Accepted solution]

It does - basically if you run a show interface gig 0/whatever your gigastack is plugged into, you will see that it is running in half duplex mode.

If you only have a single cable to each GBIC (in a star config) it will go to full-duplex.

Anything that runs half-duplex will have collisions and performance will tail off as it gets more heavily utilised... so QoS can't be guaranteed - even if packets are scheduled correctly out of the port they may be wiped out by a collision.

Go to

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns17/c649/ccmigration_09186a00800d67ed.pdf

In this QOS reference guide there is a non-favourable mention of Gigastacks...