IP Connection Excess Retransmits

Asset ID:	1-72-2096500.1
Update Date:	2017-06-29
Keywords:

Solution Type Problem Resolution Sure

Solution 2096500.1 : IP Connection Excess Retransmits

Applies to:

Oracle Communications EAGLE (Hardware) - Version EAGLE 3x.x and later
Information in this document applies to any platform.

Symptoms

For some UAMs 0536 the IP Connection exceeds retransmits.

Cause

The issue comes from the router in-between the Eagle and the Far end

The SCTP statistics show :

1. Duplicate TSNs which means the MSS does not receive some Eagle packets
2. Gaps Ack block which means some packets are lost
3. some "RTO between RMIN and RMAX inclusive" which means that retransmissions occurred
4. Some retransmissions

There is likely an issue with the router which is leading to some packet losses.

  dup tsns rcvd                       = 7
  sacks rcvd                          = 29393359
  gap ack blocks rcvd                 = 991654
  heartbeat requests rcvd             = 124245
  heartbeat acks rcvd                 = 2010263
  heartbeat requests sent             = 2010347
  ip datagrams sent                   = 90615354
  ip datagrams with data chunks sent = 53645209
  data chunks sent                    = 66727251
  retransmit data chunks sent         = 372096
  sacks sent                          = 34913212
  send failed                         = 0
  retransmit timer count              = 40256
  consecutive retransmit timeouts     = 1
  RTO between RMIN and RMAX inclusive = 4
  RTT greater than RMAX               = 0
  fast retransmit count               = 317169

Solution

Also, the far end is using the secondary path to exchange with both the primary and secondary IPs of the Eagle.
It is not a proper way of working, no loadsharing should be done on the paths of a multi-homed association.
The primary path should be used for the data packets exchanges, and the secondary path should be kept as a backup path in case of any issue and therefore should only exchange Heartbeat packets.

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