Adding existing linux media server to DD storage server

There are three common causes why a media server can't be added to the Credentials > Storage Server for Data Domain, unfortunately they all spit out the same error.  Those causes are: a) lack of network connectivity to the ddboost ports on the DD, or to the DD itself in general; b) bad ddboost username or password; and c) the media server is not in the ddboost authorized clients list on the DD.

For a) You say you can telnet to the DD, but can you connect using the storage server name defined in NetBackup to the required ports 111, 2049 & 2052: https://community.emc.com/docs/DOC-33258

For b) If the credentials are already known to the master server, you can use the GUI to simply add a checkmark next to the applicable media servers and it will re-use the credentials already in place.

For c) Check "ddboost clients show config"; by default this could be open to all using an asterisk, but if it's not you have to add the hostname of your media server to the list.  What I normally do is add the asterisk to ddboost clients, connect my media server, find the media server name reported by "ddboost show connections", add that name to ddboost clients, remove the asterisk.

As for the logs, start with nbstserv, nbemm & nbrmms in unified logging.  What I normally do, after making sure all OIDs reference the "Default" for DebugLevel and DiagnosticLevel:

1. crank up unified logging with vxlogcfg -a -p 51216 -o Default -s DebugLevel=6
2. rerun my task
3. turn down unified logging with vxlogcfg -a -p 51216 -o Default -s DebugLevel=1
4. Search the last minute of all unified logs for the media server with vxlogview -w "(prodid='NB' && prevtime='0:1:0')" -d all | less +/media-server-name

Besides the physical switch being replaced, did anything change during the network fix?  IPs, names, firewalls, VLANs?  Was the switch config properly re-applied to the new switch?

I do find it odd because even if network connectivity is lost, the NetBackup config should still show those media servers has having the storage server credentials.  I have some media servers who use ddboost over the WAN and they lose network access from time to time, but they never get removed from the storage server credentials.

I like PatS729's suggestion, and taking that one step further you can stop the media servers completely, remove them from EMM using nbemmcmd -deletehost.  When you restart the media servers they will try to check in with EMM again, if that works then connectivity from master to media seems OK and you can try adding credentials as if they were brand new media servers.  This process may require you to remove the media servers from their storage units before you can delete them from EMM, but that's part of trying to do a clean add.