Diameter Signaling Router (DSR): SCTP Maximum Segment Size Setting Under Connection Configuration Set Is Not Correctly Applied

Asset ID:	1-72-2283739.1
Update Date:	2017-07-05
Keywords:

Solution Type Problem Resolution Sure

Solution 2283739.1 : Diameter Signaling Router (DSR): SCTP Maximum Segment Size Setting Under Connection Configuration Set Is Not Correctly Applied

Applies to:

Oracle Communications Diameter Signaling Router (DSR) - Version DSR 7.1.2 and later
Tekelec

Symptoms

DSR is sending SCTP packets of more than configured "Maximum Segment Size" under "Connection Configuration Set".

Main Menu: Diameter -> Configuration -> Configuration Sets -> Connection Configuration Sets

Cause

The dsr logs showed that the setsockopt to set the "SCTP association failure retransmits" returned error

0526:065125.540 DCL-V DiameterTransport::setSock() - setsockopt(SCTP_ASSOCINFO) failed with errno=22 id=123 [24806/DiameterTransport.C:1429]

05/26/2017 09:51:25 (MME) dsr#22300{Connection Unavailable: Socket configuration failure}
.. GN_INFO/INF Connection ID=123, Peer Node FQDN=mme.epc.mnc123.mcc234.3gppnetwork.org, Errno=22
^^ [24558:DiameterLogs.C:311]

According to our code when one of the setsockopt fails then the code directly return and the remaining options of Connection Configuration Sets will also not set.

In this case setsockopt fails at parameter retransPathFailure so the parameters sctpMaxSegmentSize also fails to set.
Note: sctpMaxSegmentSize is below retransPathFailure in connection configuration set.

id=11 name=CCS retransInitialTimeout=200 retransMinTimeout=80 retransMaxTimeout=400 retransMaxTimeoutInit=0 retransPathFailure=2 retransAssocFailure=8 retransInitFailure=8 sackDelay=40 heartbeatInterval=30000 sctpSockSendSize=1000000 sctpSockRecvSize=1000000 burstMax=4 sctpNumInboundStreams=16 sctpNumOutboundStreams=16 sctpDatagramBundlingEnabled=Yes sctpMaxSegmentSize=1300 sctpFragmentationEnabled=Yes sctpDataChunkDeliveryOrdered=No provingTimeout=500 provingDwrsToSend=3 provingMode=Suspect tcTimer=30 twinitTimer=30 tdpxTimer=3 tcexTimer=3 nagleEnabled=Yes tcpSockSendSize=1000000 tcpSockRecvSize=1000000 tcpMaxSegmentSize=1024 tcpKeepAliveEnabled=No tcpKeepAliveIdleTime=1 tcpKeepAliveProbeInterval=1 tcpKeepAliveMaxCount=9 pendTransPerConn=1000 tcpCongAlgo=Cubic tcpWindowClamp=1000000 cexHostIpValidationEnabled=Yes mcl=4840

From the Connection Configuration Set we could also see that 'retransPathFailure is set to 2' and 'retransAssocFailure is set to 8'.

According to "RFC 4960 Section 8.2:Path failure", "retranAssocFailure should not be larger than the sum of retransPathFailure of all destination address".

In this case retransAssocFailure has a value greater than sum of retransPathFailure of multihomed association, so this is causing setsockopt to fail and hence all Parameters in connection configuration set below retransAssocFailure are also failing to set on the setsockopt.

RFC 4960
8.2. Path Failure Detection

Note: When configuring the SCTP endpoint, the user should avoid
having the value of ’Association.Max.Retrans’ larger than the
summation of the ’Path.Max.Retrans’ of all the destination addresses
for the remote endpoint. Otherwise, all the destination addresses
may become inactive while the endpoint still considers the peer
endpoint reachable. When this condition occurs, how SCTP chooses to
function is implementation specific

Solution

Set the retransPathFailure and retransAssocFailure in Accordance to RFC 4960 Sec 8.2 - Path Failure Detection.

In this case it was recommended to increase the value of "retransPathFailure" to 4

To change this login to Active SOAM GUI

Main Menu: Diameter -> Configuration -> Configuration Sets -> Connection Configuration Sets -> [Edit] and edit the Parameter "Number of Retransmits Triggering Path Failure".

A Bug# 26285863 has also been opened so that the SOAM GUI can correctly define the relationship between parameters retransPathFailure and retransAssocFailure

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