Telnet 3270 Clients Experience Delay During Session Startup

ID: Q216032

The information in this article applies to:

Microsoft SNA Server, versions 3.0, 3.0SP1, 3.0SP2, 3.0SP3, 4.0, 4.0SP1, 4.0SP2

SYMPTOMS

Telnet 3270 clients may experience a long delay when starting sessions. This symptom is observed when a DNS Server is not available.

CAUSE

In the event a DNS Server is not available and Use Name Resolution is configured, a Telnet client will experience a delay of up to 50 seconds during session startup. The SNA Server expects a response from the DNS Server. SNA Server will delay the session until a timeout is reached.

RESOLUTION

The TN3270 Server Service contains a configuration option titled "Use Name Resolution". Use Name Resolution is found on the General tab of the TN3270 Properties dialog box. Use Name Resolution is required if access to TN3270 sessions is restricted through workstation names. It is not required if access to TN3270 sessions is restricted through a TCP/IP address or subnet. This option should be checked only if a domain name resolver is available on the network.

MORE INFORMATION

A Microsoft Network Monitor trace shows the Telnet client and SNA Server performing a three-way TCP handshake to initiate the session within 0.003 seconds. A delay in excess of 45 seconds occurred before the Telnet session was available to the client.

Here is an example of a three-way handshake to initiate a Telnet session.


Frame 1 TCP ....S., len:    4, seq:   4505720-4505723, ack:         0, win: 8192, src: 1147  dst:   23 (TELNET)  <BR/>

Frame 2 TCP .A..S., len:    4, seq:   2489546-2489549, ack:   4505721, win:16064, src:   23 (TELNET)  dst: 1147 <BR/>

Frame 3 TCP .A...., len:    0, seq:   4505721-4505721, ack:   2489547, win:16064, src: 1147  dst:   23 (TELNET)

Here is an example of the first two frames in the Telnet session. These frames will be delayed from the first three frames by 45 seconds or more.


Frame 4 TELNET To Client With Port = 1147 

Frame 5 TELNET To Server From Port = 1147

Additional query words:

Keywords : kbenv kbnetwork
Version : WINDOWS:3.0,3.0SP1,3.0SP2,3.0SP3,4.0,4.0SP1,4.0SP2
Platform : WINDOWS
Issue type : kbprb