RCSP Study Guide - Asymmetric Route Passthrough
Asymmetric route passthrough allows connections to be passed through and an entry to be placed into the AR table. The entry is placed in the table for a default of 24 hours.
For SYN retransmissions AR will be placed in AR table at first for 10 seconds. If AR is confirmed, the timeout is increased to the default (24 hours) with a reason code updated to SYN Rexmit (confirmed AR).
If a SYN/ACK is received after we stop probing then it is placed in the table for 5 minutes with a reason code of probe filtered (not AR). If AR passthrough is disabled and we detect AR, we will not pass through the connection. A warning message is still placed in the log.
However, the alarm is not raised and no email notifications are sent. Normal functionality would be to send a probe each time. However, adding a passthough rule for 24 hours is a better approach. Sending a probe out again will save on overhead of re-transmitting the probe.