802.1Q trunk and half duplex

[annayuzhao]

I have 4*3550 switches daisy chained through WS-X3500-XL(GigaStack Stacking GBIC). They formed a half-duplex Giga connection. My question will half duplex also support trunk? I saw somewhere that trunk is only happens on Full duplex. Thanks

[eric.fairfield]

This configuration will allow for 802.1Q tagged packets to be processed even though it is half duplex.

[milan.kulik]

Hi,

you can get into trouble when daisy-chaining (using both port on GigaStack GBIC).

"Note: On GigaStack GBICs, dynamic trunking is only supported when only one port of a GigaStack GBIC is being used. If trunking is required on a GigaStack GBIC where both ports are in use, use the switchport mode trunk and switchport nonegotiate interface configuration commands on both GBIC interfaces to cause the interfaces to become trunks."

This is from 3550 Config guide, see http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12114ea1/3550scg/swvlan.htm#1096213 for the complete article.

Regards,

Milan

[andrew.butterworth]

As Milan says trunking won't be an issue if you force the ports to trunk using the 'switport nonegotiate' command. With Half-Duplex though any QoS prioritisation goes out the window so if you intend to do any VoIP or IP Telephony, don't bother......

Andy