Catalyst 3920 Token-Ring Switching
The Cisco Catalyst 3900 series of token-ring switches are menu driven and have a completely different look and feel than Cisco IOS. After you login enter the configuration menu for your basic setup. Most of your setup will normally be in the IP Configuration and the VLAN and VTP Configuration sections.
Basic Setup
TrBRF (Token-Ring Bridge Relay Function) = (Virtual Bridge)
TrCRF (Token-Ring Concentrator Relay Function) = (Virtual Ring)
Create a TrBRF. (This is your virtual bridge)
Enter the VLAN and VTP Configuration and then enter into the VTP VLAN Configuration sub-menu. There will be a menu along the bottom of the screen gives you options like, add, change, view, delete, etc. At this point add and assign the TRBrf a VLAN ID, VLAN Name, and Bridge Number. (The default Bridge Number is 0x0F and this entry is in hex)
Virtual Ring
Create a TrCRF. (This is your virtual ring)
Enter the VLAN and VTP Configuration and then enter into the VTP VLAN Configuration sub-menu. There will be a menu along the bottom of the screen gives you options like, add, change, view, delete, etc. At this point add and assign the TrCRF a VLAN ID, VLAN Name, Parent VLAN, and Ring Number.
--The Parent VLAN for the TrCRF you are configuring must match the TrBRF you want to pair with.
--The ring number is in hex.
--Leave the bridging mode in (SRB) unless there is a reason to change it.
--VLAN Ids must be unique access across all TrBRF and TrCRF configurations
Port Assignment
Assign physical ports to a specific TrCRF
Enter the VLAN and VTP Configuration and then enter into the Local VLAN Port Configuration sub-menu. Now assign your ports to the appropriate TrCRFs. If you want router interfaces plugged into the token-ring switch to be able to communicate then place those ports in the same TrCRF. If you want the router interfaces plugged into the token-ring switch to be isolated then place these ports in different TrCRFs. Your TrCRF ring numbers must be unique for each paired TrBRF.
Bridging Options
The concentrator function (trcrf) is used to move traffic between ports in the same ring (sort of like a MAU), but it uses 2 functions to handle this movement. It uses transparent bridging, where it simply learns what MAC addresses are attached to what ports in the trcrf, and source route switching, where it uses the RIF information to make a forwarding decision but doesn't modify it at all. So if all that is attached to the trcrf are devices in that ring, transparent bridging works fine. But, if you have another bridge plugged into a trcrf, the 3900 will need to use the RIF information to learn what rings are attached to what ports, so the source route switching functionality is used.
The bridging function (trbrf) is used to move traffic between ports in different rings, and is much closer in functionality to an ethernet vlan than the trcrf is. It defines the broadcast domain, and you must route to get from one trbrf to another. The trbrf gives you two options as well...source route bridging and source route transparent bridging. If you want the trbrf to move traffic to or from a ring (trcrf) based on RIF information only, configure the trcrf for source route bridging (this allows the use of duplicate MAC addresses across different trcrf's). If you want the trbrf to move traffic to or from a ring (trcrf) based on either RIF information or MAC address, configure the trcrf for source route transparent bridging (since MAC addresses are learned, all MAC addresses in the trbrf must be unique if you use SRT).
Additional Tips
Some Cisco router token-ring interface chipset don’t respond to auto-sense for speed and duplex in a token-ring environment. If have any problems at all after this point immediately go to the main configuration menu and choose Port Configuration and set your ports manually to HDX port and match the ring speed you set on the router.
1. If you need to put 2 ports under same ring. Create a TrBrf, TrCrf and put both ports under that TrCrf.
2. If you need to create 2 seperate rings and bridge between them, One TrBrf with 2 TrCrf and each port in different Crf.
3. If you want to isolate 2 rings totally from each other, create 2 TrBrf and have Crfs and ports under each.