Connectivity Problems When Using VARSUBNETTING
And MPROUTE

 
 APAR Identifier ...... PQ53384      Last Changed ........ 01/10/22
 CONNECTIVITY PROBLEMS WHEN USING VARSUBNETTING AND MPROUTE
 
 Symptom ...... IN INCORROUT         Status ........... CLOSED  PER
 Severity ................... 1      Date Closed ......... 01/10/18
 Component .......... 5735FAL00      Duplicate of ........
 Reported Release ......... 420      Fixed Release ............ 999
 Component Name TCP/IP V2 FOR V      Special Notice
 Current Target Date ..              Flags
 SCP ...................
 Platform ............
 
 Status Detail: SHIPMENT - Packaged solution is available for
                           shipment.
 
 PE PTF List:
 
 PTF List:
 Release 420   : UQ58935 available 01/10/22 (1000 )
 
 Parent APAR:    PQ51454
 Child APAR list:
 
 ERROR DESCRIPTION:
 Customer has an OSA-device connected network.  Hosts on this
 network cannot reach other hosts that are connected to the VM
 host via a point-to-point connections.
 
 From reviewing the TCP/IP server configuration file, it's
 seen that VIPA and VARSUBNETTING support are in use, in
 conjunction with the MPROUTE server (running OSPF).
 
 A NETSTAT GATEWAY command shows that correct point-to-point
 pathways are established, and connectivity exists between the
 VM host and its peers for these connections.  However, hosts
 on the OSA-connected network experiences timeouts.
 
 Tracing shows that IPUP perceives the addresses for hosts on
 the OSA-connected network to be broadcast addresses:
 
   DTCIPU040I IP-up: forward datagram
   DTCIPU041I IP-up: discard broadcast packet
 
 LOCAL FIX:
 
 PROBLEM SUMMARY:
 ****************************************************************
 * USERS AFFECTED: All z/VM TCP/IP users                        *
 ****************************************************************
 * PROBLEM DESCRIPTION: Connectivity problems when remote       *
 *                      hosts try to connect thru z/VM TCP/IP   *
 *                      to other remote hosts.                  *
 ****************************************************************
 * RECOMMENDATION: APPLY PTF                                    *
 ****************************************************************
 When UpToIp (in TCIPUP) is processing inbound packets, it
 calls IsBroadcast to determine if the packet is a broadcast.
 The IsBroadcast function is using the BsdSubnetMask from
 WhichLink (the link the packet arrived on), and incorrectly
 flagging some packets as broadcast packets. UpToIp is
 discarding them, which causes connectivity failures.
 
 PROBLEM CONCLUSION:
 The IsBroadCast function has been changed to call GetNetInfo
 to determine the route for the incoming address.  The routing
 information found (including subnet mask) is then used to
 determine if this address is a broadcast address.
 
 TEMPORARY FIX:
 
 COMMENTS:
 
 MODULES/MACROS:   TCIPUP   TCPIP
 
 SRLS:      NONE
 
 RTN CODES:
 
 CIRCUMVENTION:
 
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