Recently I needed to merge two pairs of Brocade fibre channel fabrics for one of the customers. When I was doing a bit of my own research I realised that there is very scarce information on how to do that on the Interwebs. There were a few community posts on the Brocade forums, but there seemed to be some confusion around how zoning should be configured to let the switches merge successfully. I thought I would fill the gap with this post and share my own experience.
Prerequisites
First, make sure you have the right transceivers. Short wave 8Gb FC transceivers are limited to 190m when using OM4 fibre. If you need to connect switches over a longer distance, use long wave SFP+ modules, which have maximum distance of 10km.
Second, change the default switch Domain IDs. All switches within the same fabric must have unique IDs. By default Brocade switches come with the Domain ID set to 1. If you’re merging two redundant fabrics, make sure that the second pair of the switches have Domain IDs set to 2.
Third, verify that the switches you’re interconnecting have compatible zoning configuration. Brocade is very specific on how zoning should be configured for two fabrics to merge. There are at least nine different scenarios, but we’ll touch only on three most common ones. If you want to get more details, refer to the Brocade Fabric OS Administrator’s Guide and specifically the section called “Zone merging scenarios”.
Zone merging scenarios
Scenario 1: Switch A does not have a defined configuration. Switch B has a defined configuration.
This is the most straightforward scenario when you are adding a brand new Switch A to an existing fabric. As a result of the merge configuration from the Switch B propagates to the switch A.
Scenario 2: Switch A and Switch B have different defined configurations. Switch B has an effective configuration.
This is the scenario where you have two individual fabrics with their own set of aliases, zones and defined configurations. There is a catch here. If you want to merge such fabrics, you MUST have unique set of aliases, zones and configurations on each fabric. If this requirement is not met, fabrics won’t merge and you will end up with two segmented fabrics because of the zoning conflict. You also MUST disable effective zoning configuration on Switch A.
Outage is not required, because typically you have two redundant fabrics – fabric A and B in each location. And you can do one switch at a time. If you are still concerned, implement Scenario 3.
Scenario 3: Switch A and Switch B have the same defined and effective configuration.
This is the easiest path and is what Brocade calls a “clean merge”. Under this scenario you will have to recreate the same configs on both fabrics. That means you MUST have completely identical aliases, zones and configs on Switch A and Switch B.
This is the easiest and least disruptive path if you are worried that disabling effective configuration on the switches may cause issues.
Real world scenario
In my case I went with scenario 2 for two reasons: one – it was a DR site where I could temporarily bring down both fabrics and two – I didn’t need to manually add aliases/zones/configs to the switches as I would have to in scenario 3. Once fabrics are merged, zones from Switch B propagate to Switch A and you can simply combine them in one zone in the GUI, which is just a few mouse clicks.
Here is the step by step process. First step is to change Domain IDs on the second pair of switches. You can do that both from GUI and CLI. Bear in mind that even if you’ve picked scenario 3 as the least disruptive approach for merging zones, changing Domain IDs will still be disruptive. Because switch has to be disabled before making the change.
From the Web Tools go to Switch Administration, disable the switch in the Switch Status section, type in the new Domain ID and re-enable the switch:
If you want to take the CLI path, run the following. Switch will ask you a series of questions. You can accept all defaults, except for the Domain field:
> switchdisable
> configure
> switchenable
> fabricshow
Next disable the effective configuration on the Switch A either from GUI or CLI:
> cfgdisable
> cfgactvshow
At this point you can interconnect the switches and you should see the following log entry on Switch A:
The effective configuration has changed to SWITCHB_CONFIG
The fabrics are now merged an you should see both switches under the Web Tools. If you see the switch in the Segmented Switches section, it means that something went wrong:
Clean up steps
Once the fabrics are merged you will see all zones in the Zone Admin interface, however, the effective configuration will be configuration from the Switch B. You will need to create a new configuration which combines all zones to enable connectivity between the devices connected to the Switch A.
From the operational perspective you can now manage zoning on either of the switches and when you save or enable a configuration it will propagate to all switches in the fabric automatically.
If you have redundant fabrics, which you normally do, repeat the steps for the second pair of switches.
Conclusion
Steps described in this post are for a basic switch setup. If you have a non-standard switch configuration or using some of the advanced features, make sure to check “Zone Merging” section in the Fabric OS Administrator’s Guide for any additional considerations.
Let me know if this was helpful.
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