Error setting up AG between 1 primary and 2 secondaries

Question

Setting up AlwaysOn AG from Primary to 2 secondary replicas. Both async.
Primary to replica1 works fine and completed setup.
Primary to replica2 gives below errors.
On primary (LABSVR6)
A connection timeout has occurred while attempting to establish a connection to availability replica 'LABSVR8' with id [99F3037B-D00A-4421-AA3E-0E1FEAD28CDA]. Either a networking or firewall issue exists, or the endpoint address provided for the replica is
not the database mirroring endpoint of the host server instance.
On Replica2 (LABSVR8)
A connection timeout has occurred while attempting to establish a connection to availability replica 'LABSVR6' with id [B3F0C0F0-3742-4607-89F7-88197334E802]. Either a networking or firewall issue exists, or the endpoint address provided for the replica is
not the database mirroring endpoint of the host server instance.
And when trying to join manually through Management Studio, it says:
Failed to join the instance 'LABSVR8' to the availability group 'SQLAG'. (Microsoft.SqlServer.Management.SDK.TaskForms)
Failed to join local availability replica to availability group 'SQLAG'.  The operation encountered SQL Server error 41106 and has been rolled back.  Check the SQL Server error log for more details.  When the cause of the error has been resolved,
retry the ALTER AVAILABILITY GROUP JOIN command. (Microsoft SQL Server, Error: 41158)
Both using same domain service account for startup - which is anyways added with SYSADMIN.
Primary to replica1 is working fine.
Primary to replica2 is having above problem when joining.
Any suggestions?
TIA

Answer 1

Hello,
not a firewall or SPN issue because primary to replica1 setup went just fine.
That just means from the primary to replica1 you don't have an issue. It means nothing for primary to replica2 or you wouldn't be having the problem.
i am able to connect to all servers from all servers using Management Studio.
This means the default TSQL endpoint is working (1433 for default instances) but AOAG works over a mirroring tcp endpoint. This just proves that nothing is blocking the tsql endpoint.
Some next steps:
1. Stop the mirroring endpoint on replica2 and start it again. Check the errorlog to see any errors that may have come up from starting it.
2. Check the replica2 server name, use the FQDN and double check to make sure DNS has the correct IP associated with the record.
3. If the endpoint spans a subnet, make sure a route exists.
4. Attempt to manually telnet to the mirroring endpoint on replica2. If it works you'll get a blinking cursor with a black screen. If not you'll get an error.
Post back any results, please.
Sean Gallardy | Blog
MCM 2008
MCSM:Data Platform Charter Member