When a device alias mode is changed from basic mode to enhanced mode, the corresponding applications are informed about the change. The applications then start accepting the device alias-based configuration in the native format.

Note	Because the device alias was previously running in the basic mode, the applications do not have any prior native device alias configuration.

The applications check for an existing device alias configuration in the native format. If the device alias is in the native format, the applications reject the request, and the device alias mode cannot be changed to basic.

All the native device alias configurations (both on local and remote switches) must be explicitly removed, or all the device alias members must be replaced with the corresponding pWWNs before changing the mode back to basic.

If device alias distribution is turned on, it is distributed to the other switches in the network whenever there is a change in the mode. You cannot change the mode from basic to enhanced unless all the switches are upgraded to Release 3.1. The device alias enhancements will not apply unless the entire fabric is upgraded to Release 3.1.

Note	After all the switches are upgraded to Release 3.1, you cannot automatically convert to enhanced mode. The switches do not have to be changed to enhanced mode; you can continue working in the basic mode.

From the Cisco MDS NX-OS Release 7.3(0)D1(1), the Device Alias Diffs-Only Distribution feature is supported on the Cisco MDS switches.

When this feature is enabled on all the switches in a fabric, only the session commands are sent across the fabric instead of the entire database, which helps ensure better scalability.

DDAS supports 20,000 entries when all the switches in a fabric have the Device Alias Diffs-Only Distribution feature enabled. Note that this feature is enabled by default.

Note	Ensure that all the switches in a fabric are running Cisco MDS NX-OS Release 7.3(0)D1(1) with the Device Alias Diffs-Only feature enabled.

If two fabrics are running different device alias modes, the device alias merge fails. There is no automatic conversion of one mode to the other during the merge process. You will need to resolve the issue.

Note	Release 3.0 switches run in basic mode.

At the application level, a merger takes place between the applications and the fabric. For example, zone merge occurs when the E port is up, and the IVR,PSM/DPVM merge occurs due to CFS. This merge is completely independent of the device alias merge.

If an application running on an enhanced fabric has a native device alias configuration, the application must fail the merge even if the other fabric is can support the native device alias-based configuration, but is running in the basic mode. You will need to resolve the issue. After the device alias merge issue is resolved, each application must be fixed accordingly.

The following issue occurs when there is a device alias database mismatch in the switches that are a part of the same fabric:

The device alias associated to a pWWN is present in the port security/DPVM database even if the respective device alias member is not present in the switch. The device alias associated to a pWWN is missing in the port security/DPVM database even if the respective device alias member is present in the switch.

If two fabrics are running in different modes and the device alias merge fails between the fabrics, the conflict can be resolved by selecting one mode or the other. If you choose the enhanced mode, ensure that all the switches are running at least the Release 3.1 version. Otherwise, the enhanced mode cannot be turned on. If you choose the basic mode, the applications running on the enhanced fabric have to comply with the device alias merge.

The device alias merge fails because of mode mismatch, but the application merge succeeds if it does not have any native device alias configurations.

If a native device alias configuration is attempted on an application from a Release 3.1 switch, the commit must be rejected because of device alias mode mismatch on some of the applications.

Note	The applications should not accept any native device alias configuration over SNMP if the device alias is running in the basic mode on that particular switch.

Note	Confcheck will be added when the enhanced mode is turned on and removed when it is turned off. Applications should add confcheck if they have a device alias configuration in the native format, and remove it after the configuration is removed.

Device aliases have the following features:

• Device alias information is independent of your VSAN configuration.
• Device alias configuration and distribution is independent of the zone server and the zone server database.
• You can import legacy zone alias configurations without losing data.
• The device alias application uses the Cisco Fabric Services (CFS) infrastructure to enable efficient database management and distribution. Device aliases use the coordinated distribution mode and the fabric-wide distribution scope (refer to the Cisco MDS 9000 Family NX-OS System Management Configuration Guide ).
• When you configure zones, IVR zones, or QoS features using device aliases, and if you display these configurations, you will automatically see that the device aliases are displayed along with their respective pWWNs.

Device aliases have the following requirements:

• You can only assign device aliases to pWWNs.
• The mapping between the pWWN and the device alias to which it is mapped must have a one-to-one relationship. A pWWN can be mapped to only one device alias and vice versa.
• A device alias name is restricted to 64 alphanumeric characters and may include one or more of the following characters:
  • a to z and A to Z
  • 1 to 9
  • - (hyphen) and _ (underscore)
  • $ (dollar sign) and ^ (up caret)

Note	If the device-alias name is 64 characters in length, the DPVM and other application databases do not update properly. Restrict the number of characters in the device-alias name to 63.

Table 1 compares the configuration differences between zone-based alias configuration and device alias configuration.

By default, device alias distribution is enabled. The device alias feature uses the coordinated distribution mechanism to distribute the modifications to all switches in a fabric.

If you have not committed the changes and you disable distribution, then a commit task will fail.

Displays a Failed Status

switch# show
 device-alias status
Fabric Distribution: Disabled
Database:- Device Aliases 25
Status of the last CFS operation issued from this switch:
==========================================================
Operation: Commit
Status: Failed (Reason: Operation is not permitted as the fabric distribution is
 currently disabled.)

Note	From the Cisco MDS NX-OS Release 6.2.9 onwards, the ASCII configuration replay takes longer time for DDAS (Distributing Device Alias Services) without the write erase command.

When you perform the first device alias task (regardless of which device alias task), the fabric is automatically locked for the device alias feature. Once you lock the fabric, the following situations apply:

• No other user can make any configuration changes to this feature.
• A copy of the effective database is obtained and used as the pending database. Modifications from this point on are made to the pending database. The pending database remains in effect until you commit the modifications to the pending database or discard (abort) the changes to the pending database.

As a part of the device-alias configuration best practices, the following guidelines need to be adopted within a device-alias session:

If a device-alias name is reused while configuring a rename command, then the command fails and gets moved to the rejected list.

switch(config-device-alias-db)# device-alias name dev10 pwwn 10:10:10:10:10:10:10:10
switch(config-device-alias-db)# device-alias rename dev10 new-dev10
Command rejected. Device-alias reused in current session :dev10
Please use 'show device-alias session rejected' to display the rejected set of commands and for the device-alias best-practices recommendation.
switch(config-device-alias-db)#       

switch(config-device-alias-db)# device-alias name dev11 pwwn 11:11:11:11:11:11:11:11
switch(config-device-alias-db)# no device-alias name dev11
Command rejected. Pwwn reused in current session: 11:11:11:11:11:11:11:11 is mapped to device-alias dev11
Please use 'show device-alias session rejected' to display the rejected set of commands and for the device-alias best-practices recommendation.
switch(config-device-alias-db)#

switch(config-device-alias-db)# device-alias rename da3 new-da3
switch(config-device-alias-db)# device-alias name da3 pwwn 2:2:2:2:3:3:3:3
Command rejected. Device-alias name reused in current session: da3
Please use 'show device-alias session rejected' to display the rejected set of commands and for the device-alias best-practices recommendation.
switch(config-device-alias-db)#  

switch(config-device-alias-db)# show device-alias session rejected
To avoid command rejections, within a device alias session
Do not reuse:
a) a device alias name while configuring a rename command
b) a PWWN while configuring an add or delete command
c) a device alias name already renamed while configuring add command
 
Rejected commands must be committed in a separate device alias session
which may cause traffic interruption for those devices. Plan accordingly.
Refer to this command in the NX-OS Command Reference Guide
for more information about device alias configuration best practices
 
Rejected Command List
---------------------
device-alias rename dev10 new-dev10
no device-alias name dev11
device-alias name da3 pwwn 02:02:02:02:03:03:03:03
switch(config-device-alias-db)# #  

If you have performed a device alias task and have forgotten to release the lock by either committing or discarding the changes, an administrator can release the lock from any switch in the fabric. If the administrator performs this task, your changes to the pending database are discarded and the fabric lock is released.

Tip	The changes are only available in the volatile directory and are subject to being discarded if the switch is restarted.

To clear device-alias session, use the clear device-alias session command in CONFIGURATION mode.

switch(config)# clear device-alias session

To verify the status of the clear operation, use the show device-alias session status command.

switch(config)# show device-alias session status
Last Action Time Stamp     : None
Last Action                : None
Last Action Result         : None
Last Action Failure Reason : none

To clear all the database content, use the clear device-alias database command in CONFIGURATION mode.

switch(config)# clear device-alias database
To verify the status of the clear device-alias database 
command, use the show device-alias database 
command.
switch(config)# show device-alias database

To clear all the statistics, use the clear device-alias statistics command in CONFIGURATION mode.

switch# clear device-alias statistics

1.    switch# config t

2.    switch(config)# device-alias import fcalias vsan 3

switch(config)# 

switch# show zoneset
zoneset name s1 vsan 1
  zone name z1 vsan 1
    pwwn 21:01:00:e0:8b:2e:80:93 [x] <---------------Device alias displayed for each pWWN.
    pwwn 21:00:00:20:37:39:ab:5f [y]
zone name z2 vsan 1
    pwwn 21:00:00:e0:8b:0b:66:56 [SampleName]
    pwwn 21:00:00:20:37:39:ac:0d [z]

switch# show
 zoneset active
zoneset name s1 vsan 1
  zone name z1 vsan 1
  * fcid 0x670100 [pwwn 21:01:00:e0:8b:2e:80:93] [x]
    pwwn 21:00:00:20:37:39:ab:5f [y]
  zone name z2 vsan 1
  * fcid 0x670200 [pwwn 21:00:00:e0:8b:0b:66:56] [SampleName]
    pwwn 21:00:00:20:37:39:ac:0d [z]

Use the clear device-name statistics command to clear device alias statistics (for debugging purposes):

switch# clear device-alias statistics

This section lists the best practices that you should follow when creating and using device aliases:

• Device aliases should be used to simplify the management of world wide names (WWNs) whenever possible. It is easier to identify devices with aliases rather than with WWNs. Hence, you should assign aliases to WWNs to easily identify the WWNs.

• Device-alias names are case-sensitive.

• Operate device aliases in Enhanced mode whenever possible. In Enhanced mode, applications accept a device-alias name in its native format, rather than expanding the alias to a port world wide name (pWWN). Because applications such as zone server, Inter-VSAN Routing (IVR), Port Security Manager (PSM), and Dynamic Port VSAN Membership automatically track and enforce device-alias membership changes, you have a single point of change.

  Note	Interop mode VSANs do not accept Enhanced mode configurations.

• Preplan device-alias configurations and implement a consistent naming convention.

• Keep documented backups of all device-alias configurations.

• Plan for what the final device-alias database should be after the merge, before attempting to resolve merge failures. This can prevent traffic disruptions caused by accidentally overwriting device-alias entries.

  Caution

  Avoid performing a blank commit to resolve Cisco Fabric Services (CFS) merge failures. A blank commit overwrites the device-alias databases on all the switches with the device-alias database on the local switch.

  Note	A blank commit is a device-alias commit that is used when there are no changes (including mode changes), or when it is okay to overwrite the device-alias databases on the remote switches with the local switch’s device-alias database.

  Device alias mismatches might occur because of the following reasons:

  • Duplicate Device-Alias Names—Same device-alias name, but different pWWNs. In such a scenario, the show device-alias merge status command displays the reason for the merge failure as Reason: Another device-alias already present with the same name.

  • Duplicate pWWNs—Different device-alias names, but same pWWN. In such a scenario, the show device-alias merge status command displays the reason for the merge failure as Reason: Another device-alias already present with the same pwwn.

  Note

  Each time device-alias changes are committed, the running configuration should be copied to the startup configuration on all the switches that were updated. Use the copy running-config startup-config fabric command to copy the running configuration to the startup configuration for all the switches in the fabric. If you do not copy the running configuration to the startup configuration after the device-alias changes are committed, and if the switch reloads, or loses power and restarts, the startup configuration will not have the correct device-alias database and merge failure will occur.

This section provides information about how to resolve merge failures.