Commands for Configuring Aggregated VLANs on Device C
Because device C is aggregating channel VLANs from devices A and B into a single path, you need to change the tag profile and enable VLAN aggregation.
deviceC(config)# tag-profile 9100 deviceC(config)# aggregated-vlan deviceC(config)# vlan 910 by port deviceC(config-vlan-910)# tagged ethernet 1/1/17 deviceC(config-vlan-910)# untagged ethernet 1/1/11 to 1/1/12 deviceC(config-vlan-910)# exit deviceC(config)# interface ethernet 1/1/11 to 1/1/12 deviceC(config-mif-1/1/11-1/1/12)# tag-profile enable deviceC(config-mif-1/1/11-1/1/12)# exit deviceC(config)# write memory