Session Recovery Detection
When SSR routers peer, forward and reverse flows are established between devices as traffic flows from client to server through the routers. As failures occur in networks, the SSR communicates with its peers in an effort to preserve client to server communication across alternate available pathways. Traffic destined to flows that no longer exist result in a metadata response from the SSR. This response may falsely indicate that the SSR is listening and responding to wayports - which it does not.
An alternate approach to SSR communication for session recovery has been created,
session-recovery-detection. The feature has two modes, the default
packet-based detection, and
inactivity-based detection which has a configurable timeout. When inactivity-based detection is enabled, the originating node monitors activity on the flow. If no activity is detected for the specified time, the originator will add an additional metadata attribute called
session-health-check to the next packet. The
session-health-check attribute is validated by the receiving node. If the flow on the receiving node does not exist, it generates an
enable-metadata message back to the originator.
The activity is monitored for both forward and reverse flows, and if forward flow is deemed to be idle, the
session-health-check attribute will be generated for the reverse traffic.
How It Works
The following configuration parameter is available under Authority:
Session Recovery Detection
Session Recovery Detection has two modes:
inactivity-basedThis has a configurable
inactivity-timeoutwith a default of 5 seconds.
Because this feature uses a request/response mechanism, all SSR's using this feature must be upgraded.
Show Stats Commands
show stats commands provide insight into session information. For additional details, select the link for each stat.
show stats packet-processing action failure metadata session-health-check-buffer-allocation
show stats packet-processing action failure metadata session-health-check-timeout
show stats packet-processing action failure metadata session-health-check-timeout-forward-pinhole-flow
show stats packet-processing action failure metadata session-health-check-timeout-reverse-pinhole-flow
show stats packet-processing action success metadata added-session-health-check
show stats packet-processing action success metadata generated-session-health-check-acknowledgement
show stats packet-processing action success metadata received-session-health-check-acknowledgement
show stats packet-processing action success metadata received-stale-session-health-check-acknowledgement
show stats packet-processing action success metadata sent-session-health-check-acknowledgement
show stats service-area received reverse-packets-for-stuck-pinhole-session