Welcome to Dell Technologies Connectrix Cisco MDS - Break-fix Series.
VSAN is down (Isolation due to domain overlap). Reference Dell Knowledge Base Article # 041418 and 203078. This video was created to: Demonstrate how to resolve Domain ID overlap.
There should be no domain ID overlapping for a successful fabric merge. Isolation due to domain overlap is applicable only on E-ports and TE ports.
This video presents the following: If two switch fabrics with two or more switches are connected and both fabrics have switches within the domain ID already assigned, the E ports that are used to connect two fabrics are isolated or VSAN is isolated on (TE) ports.
In this image, Fabric 1 has Domain 110 and same Domain 110 on Fabric 2. Hence, the E ports are down due to overlapping domain IDs.
When a switch fails to establish adjacency with its neighboring switch, the failure might be the result of a domain ID conflict. Domain IDs are configured on a per-VSAN basis.
So, it is possible that a switch can see all switches in one VSAN, but be isolated in another. When to do this: The E-ports that are used to connect two fabrics can become isolated when both of the following conditions occur: Condition 1: Both fabrics have switches with the same domain ID already assigned. Condition 2: The auto-reconfigure option is disabled. (This option is disabled by default).
To resolve an FC domain ID overlap: Change the overlapping static domain ID by manually configuring a new static domain ID for the isolated switch.
Or disable the static domain assignment and allow the switch to request a new domain ID after a fabric reconfiguration. All devices attached to the switch in the VSAN get a new FCID when a new domain ID is assigned.
Some hosts or storage devices may not function as expected if the FCID of the host or storage device changes. Before you begin: You may see the following system message in the message log when a domain ID overlap occurs.
Refer to the following steps to assign a new domain ID using CLI. In this demo, we are going to resolve "isolation due to domain overlap" by assigning new static domain ID using CLI.
MDS-9100-B and 9200-B are ISL through interface fc1/2. Verify the operation of fc1/2. You can see that VSAN 301 is isolated on both sides. Verify the EISL trunk configuration.
Check the fiber channel domain information for VSAN 301 on both switches. Notice that both switches state that they are the principal switch and the interface fc1/2 is an isolated state.
Look at the "Current domain ID". The value "239" is the same on both switches. The domain IDs have to be unique on all devices in the fiber channel domain.
You should fix the configuration. On MDS-9100-B, configure a different domain value for VSAN 301. Verify the domain information on MDS-9100-B again. fc1/2 is still isolated, and 239 is still the runtime domain ID. But now "100" is the static domain ID. Restart the "fcdomain" process to apply the changes to runtime.
Verify "fcdomain" again. Now the current domain ID is 100, but fc1/2 is still isolated. Reset the interface fc1/2. Verify the domain information again.
Now you can see that the role of interface fc1/2 changed from "Isolated" to "Upstream". MDS-9100-B is now subordinate switch. Verify interface fc1/2 to confirm that connectivity within the fabric is now established. You can see that the status of VSAN 301 changed from "Isolated" to "Up".
The issue has been fixed. Important notes: fcdomain restart vsan is non-disruptive of data traffic over the entire network, but it can be disruptive on a switch if its configured domain is static and numerically not the same as its runtime domain ID. fcdomain restart disruptive vsan disrupts data traffic across all switches in the VSAN.
You can use a fabric reconfiguration to reassign domain IDs and resolve any overlapping domain IDs. If you enable the auto-reconfigure option on both switches before connecting the fabric, a disruptive reconfiguration occurs.
The RCF functionality would automatically force a new principal switch selection and cause new domain IDs to be assigned to different switches.
The auto-reconfigure option prevents isolation by forcing a disruptive restart of the VSAN. However, a disruptive restart is still required if auto-reconfiguration is enabled after isolation occurs.
The auto-reconfigure option must be enabled on all switches. A disruptive reconfiguration might affect data traffic. Cisco MDS 9000 family fabric switches that are operating in Cisco NPV mode do not join a fabric because they pass traffic between core switch links and end devices, which eliminate the domain IDs for these switches.
Refer to the following for more information: Dell EMC KB article # 041418 and 203078. Cisco MDS 9000 Family CLI Configuration Guide - Chapter: Configuring Domain Parameters. Cisco MDS 9000 Family Troubleshooting Guide - Chapter: FC Domain ID Overlap.
Thank you for watching.
