0536 - IP Connection Excess Retransmits

An SCTP association has excessive retransmissions. The retransmission errors may cause a connection to congest and fail in the presence of a sufficiently high load.

Note:

IP Connection UAMs 0086 (Congested), 0535 (Restricted), and 0536 (Excess Retransmits) conditions can occur simultaneously. However, only one alarm per device can be displayed at a time. If two or more are present, the display of these alarms is prioritized as follows:

1. 0086 - IP Connection Congested (MSUs are being dropped)
2. 0536 - IP Connection Excess Retransmits (MSUs may be dropped. The EAGLE 5 ISS sustains a certain rate of dropped MSUs without triggering this alarm, then issues UIM 0536 when that rate is exceeded.)
3. 0535 - IP Connection Restricted (MSUs are being transmitted at reduced rate. A path of a multi-homed association has failed. )

Example

   RLGHNCXA21W 06-12-07 12:01:43 EST  EAGLE 35.6.0 
*  1111.0536 * IP7 assoc1234567890         IP Connection Excess Retransmits

Alarm Level: Minor

Recovery

This error may be due to:

• Misconfiguration or improper tuning of SCTP attributes to match the network conditions and traffic volumes

• Packet loss

• Excessive round-trip times

• The receive buffer of the SCTP peer being full for extended periods (probes by Eagle SCTP to update window size may result in discards by the peer)

• Timer settings that are too close in value

1. Use the following pass commands to aid in determining the cause of the error:
   • sctp - gives how many retransmits are occurring
   • assocrtt - gives round-trip time information on a per-association basis
   • netstat - gives information on interface and per-protocol statistics (IP, SCTP and others)
   • ping - gives information on reachability and round-trip times
2. If the error is due to configuration problems, correct the configuration.
3. If the number of retransmissions is within expected values, the alarm threshold can be changed.

   Note:

   Changing the threshold does not affect link traffic, it only affects the alarm trigger level.
   1. Use the rtrv-assoc:aname=xxxx command to determine the current retransmit threshold (RTXTHR) value.
   2. Use the chg-assoc:aname=xxxx command to change the retransmit threshold (RTXTHR) value. Increasing the value will make the alarm less likely to occur.

   Refer to the Commands Manual for additional information.

4. False retransmissions can occur if the RTO and SACK timer on either side of the connection are close in value. Refer to the SIGTRAN User Guide for more information about these timers.