Endpoint mapper client issue

[Samuel Cabrero]

Hi team,

while working to add witness protocol support to the cifs Linux kernel
client and I have found what I think is a problem in the Windows Server
2019 Endpoint Mapper.

When the client asks to the Endpoint Mapper at the IP address
associated to the clustered file server role for the witness service
port, it does not return the protocol tower when using 32bit NDR until
a client using 64bit NDR transfer syntax asks.

I have attached four traces where:
- 192.168.101.200 is the IP address associated to the clustered file
server role
- 192.168.101.51 is a Windows client
- 192.168.155.101 is a Samba client

After booting up the cluster, in the first trace (step 1) there is a
Samba client offering 32bit NDR transfer syntax (frame 48) and calling
epm_map (frame 51). The server does not return the protocol tower
(frame 52). 

In the second trace (step 2) a windows client does the same but this
time 64bit NDR transfer syntax is used (frame 237) and the server
returns the protocol tower (request in frame 240, response in frame
282).

The third step is the same as the first one, but this time the server
returns the protocol tower (request in frame 62, response in frame 63).

I have also modified the samba client to add the IP address in the
fifth floor in the step 1 and it does not change anything, the server
does not return the tower until a client asks using 64bit NDR.

Have you ever seen this behavior before? Can we discard a problem in
our side and ask dochelp?

Thanks.

-- 
Samuel
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