IST2246I

Explanation
  This unsolicited message is issued at 30 second
intervals as long as data flow  continues to be stalled for an RTP
pipe. 
 In the message text: puname
The name of the HPR PU.
cpname
The name of the CP at the other end of the pipe. 

System action
 HPR continues to wait for the RTP partner to
acknowledge receipt of the network layer packets (NLPs) identified
as causing the transmission stall. When all of those NLPs are acknowledged,
the transmission stall is considered  alleviated and message IST2247I
is issued.

Operator response
 Perform the following steps to alleviate
the transmission stall:  
 If the RTP pipe traverses EE and the following conditions are
true, verify that the firewalls are configured to allow ICMP errors
to flow on all hops of the connection: Path MTU discovery is enabled for either IPv4 or IPv6 EE connections.
See the PMTUD start option information
in z/OS Communications Server: SNA Resource Definition
Reference.
Firewalls are used in the configuration.

 If the firewalls are not allowing ICMP errors to flow, this
could be the cause of the transmission stall.  Disable path MTU discovery
for EE connections until the firewalls are configured to allow ICMP
errors to flow:  Issue the MODIFY procname,VTAMOPTS,
PMTUD=NO command to temporarily disable path MTU discovery.
Contact the system programmer to permanently disable path MTU
discovery for IPv4 and IPv6 EE connections.

If the transmission stall persists, force an RTP path switch by
issuing the MODIFY procname,RTP, ID=rtp_pu_name
command.
If the RTP path switch does not relieve the transmission stall,
consider ending the stalled sessions by issuing the VARY procname,INACT,ID=rtp_pu_name,TYPE=FORCE
command to deactivate the HPR PU.  If you want VTAM® to automatically end stalled RTP pipes
after a specified amount of time, use the HPRSTALL start option. See
the HPRSTALL start option information
in z/OS Communications Server: SNA Resource Definition
Reference.

System programmer response
 If you want path MTU discovery for
IPv4 and IPv6 Enterprise Extender  connections permanently disabled,
specify PMTUD=NO in the appropriate ATCSTRxx  VTAM start list.

User response
 Not applicable.

Problem determination
 If transmission stalls are prevalent
and persistent, contact VTAM support
for  instructions about gathering documentation for problem determination.
 If you have access to IBMLink, search for known problems with similar
symptoms.
If no applicable matches are found, or if you do not have access
to IBMLink,
obtain a diagnostic dump for this error and report the problem to IBM®. If you have access to IBMLink, the
problem can be reported to IBM using
the Electronic Technical Report (ETR) option on IBMLink.

Source
 z/OS® Communications
Server SNA

Module
 You can display the module that issues a SNA message
in the message by setting the MSGMOD start option to YES.  See Adding the originating module to the message text for more information about the MSGMOD
start option.

Routing code
 2

Descriptor code
 4

Automation
 Not applicable.

Example
  IST2246I XMIT STALL CONTINUES FOR RTP CNR0002F TO NETA.SSCP1A