Description

SRX series high end product have the first 5 UDP packets out of order. This is product limitation.

Symptoms

First 5 UDP packets are out of order with high end SRX devices, both SPC2 and SPC3. 

Solution

This is a product limitation and occurs since day 1.

When a packet comes to flow, it will create a pending session and run first path process if a session isn't already created. The following packets will hit the pending session and queue on the pending queue. All queued packets will be flushed out and re-run flow fast-path once session creation is done. Because of multi-thread processing, there are two cases the packet order might be changed:

  1. Packets may be queued to a session pending queue out of order

  2. After all queued packets are flushed, flow fast-path processing may complete out of order.

The issue only occurs for the first several packets that hit the pending session. Once the session is valid, Packet-Ordering-Thread will send the packet out in order.