> # Domain IDs

> Domain IDs uniquely identify a switch in a VSAN. A switch may have different domain IDs in different VSANs. The domain ID is part of the overall FC ID.

> The configured domain ID can be preferred or static. By default, the configured domain ID is 0 (zero) and the configured type is preferred.

> Note The 0 (zero) value can be configured only if you use the preferred option.

> If you do not configure a domain ID, the local switch sends a random ID in its request. We recommend that you use static domain IDs.

> When a subordinate switch requests a domain, the following process takes place:

> 1. The local switch sends a configured domain ID request to the principal switch.
> 2. The principal switch assigns the requested domain ID if available. Otherwise, it assigns another available domain ID.

> The behavior for a subordinate switch changes based on three factors:

> - The allowed domain ID lists.
> - The configured domain ID.
> - The domain ID that the principal switch has assigned to the requesting switch.

> In specific situations, the changes are as follows:

> - When the received domain ID is not within the allowed list, the requested domain ID becomes the runtime domain ID and all interfaces on that VSAN are isolated.
> - When the assigned and requested domain IDs are the same, the preferred and static options are not relevant, and the assigned domain ID becomes the runtime domain ID.
> - When the assigned and requested domain IDs are different, the following cases apply:
> - If the configured type is static, the assigned domain ID is discarded, all local interfaces are isolated, and the local switch assigns itself the configured domain ID, which becomes the runtime domain ID.
> - If the configured type is preferred, the local switch accepts the domain ID assigned by the principal switch and the assigned domain ID becomes the runtime domain ID.

> If you change the configured domain ID, the change is only accepted if the new domain ID is included in all the allowed domain ID lists currently configured in the VSAN. Alternatively, you can also configure zero-preferred domain ID.

> Tip When the FICON feature is enabled in a given VSAN, the domain ID for that VSAN remains in the static state. You can change the static ID value but you cannot change it to the preferred option.

> Note In an IVR without NAT configuration, if one VSAN in the IVR topology is configured with static domain IDs, then the other VSANs (edge or transit) in the topology should also be configured with static domain IDs.
> In an IVR NAT configuration, if one VSAN in the IVR topology is configured with static domain IDs, then the IVR domains that can be exported to that VSAN must also be assigned static domains.

> Caution | You must restart the fcdomain if you want to apply the configured domain changes to the runtime domain.

> Note If you have configured an allowed domain ID list, the domain IDs that you add must be in that range for the VSAN. See the "Configuring Allowed Domain ID Lists" topic.

> Copyright 2010-2015, Cisco Systems, Inc. All rights reserved.