Trunk Porting a Cisco Catalyst 3850 to a Cisco Catalyst 3750-X Series

[ctalavat]

I am trying to install a Cisco Catalyst 24 port 3750-X series switch and need to trunk port from a Cisco Catalyst 3850.  I'm using gi1/0/21 on both switches for consistency.  I think I have the correct commands configured but I want to make sure before hooking them up.

3850: config t > interface gi1/0/21 > switchport mode trunk > end

3750: config t > interface gi1/0/21 > switchport trunk encapsulation dot1q > switchport mode trunk > end

Thank you. 

[MHM Cisco World]

It easy yes the command is correct, but interconnect two SW you need to check first the STP mode in both SW. 

Otherwise loop can happen or vlan is BLK. 

[ctalavat]

Both switches have spanning-tree portfast in the configuration.

[MHM Cisco World]

STP mode 
i.e. 
MST 
PVST 
R-PVST 
RSTP
these mode

[ctalavat]

3850: rapid-pvst mode

3750: pvst mode

[MHM Cisco World · Accepted solution]

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/72836-rapidpvst-mig-config.html

According to cisco doc. Above there is no problem if some SW use r-pvst and other use pvst.

Check doc.  Above (mixed mode)

[ctalavat]

I got everything to work. Thank you for your assistance.