Will reducing the TCP 2msl value helps in reducing CPU utilization ?

Products

• ProxySG Software - SGOS

Issue/Introduction

Each TCP connection will have a timer of its own as it enters the TCP TIME_WAIT state. Once it completes the TCP TIME_WAIT period, it will be cleared from the TCP connections table. As the clearance is not a scheduled/batch process (i.e. not performed periodically), reducing this value might provide little relieve on CPU utilization.

If there are any CPU usage improvements as a result of changing this value, it might be the result of :

- keeping the connection open for a shorter period of time which would reduce the number of PCB entries which could slightly reduce the amount of time required to find a connection
- The local port will be held for a shorter period of time which would make it easier to find an open local port to bind to when initiating new connections.
 

SG200#configure terminal
SG200#(config)tcp-ip tcp-2msl ?
 <seconds>
SG200#(config)tcp-ip tcp-2msl 60
  ok
SG200#(config)exit

SG200#show tcp-ip
.....
  TCP 2MSL timeout:             60 seconds           <<<<< Default value
.....

Resolution

2msl has been reduced to 60 seconds default as of 7.2.1.1 and later. However, this is not automatically applied when upgrading devices.

Additional Information

Note: TCP Time_Wait in large numbers is normal behavior and does not inherently mean there's an issue, and should not be utilized as a cause for concern (As of 7.3.17.1 and later). TIME_WAIT connections can be reused when a SYN containing a higher sequence number is received