Re: Concerns about changing TCP/IP keep alive time.

Hi Rob,

This parameter (TCPKEEPALV) controls how often (for each TCP connection) the system checks to see if the "other end" is still connected. (By 'other end', I mean the computer or other device to whom the TCP session is connected.)

Why might you want to set this to a higher number? Off the top of my head:

1) Wireless connections (or similar) where the 'other end' goes in an out of coverage areas. If the system sends a "keep-alive" (i.e. checks the status of the connection) while it's out of coverage area, IBM i will disconnect it. So setting this to a higher number reduces the disconnections, since it checks less frequently.

This would also apply to any network connection that's not always reliable (i.e. network goes up/down often)

2) To reduce network traffic. Sending a keep-alive obviously requires something to be sent over the network (though, it's not much.) If the system has thousands of TCP connections and the TCPKEEPALV value is set too low, this might result in a lot of extra network transmissions.

(However, with today's fast networks, I personally find this reason to be rather silly. It made sense historically, though.)


Why might you want to want to set TCPKEEPALV to a lower number?

1) Because it's taking the system too long to detect that a connection has been dropped. Checking the connection more frequently will detect abnormal disconnects much faster.

(That's the only reason I'm aware of -- but it's a biggie.)


Personally, I have mine set to TCPKEEPALV(2), and will protest loudly if someone tells me to make it higher.



On 2/23/2012 1:03 PM, rob@xxxxxxxxx wrote:

I recently got an update to a Domino ticket that went like this:
Looking at the current data from netstat the GDDATA system has 2872
sessions from LDAP in close2 status.
These are sessions that will Eventually close.

One thing we can do is drop the keep alive time.

This is the TCP parameter that limits how long a dead but not closed
session will hold the socket open.
The default is 2 hours, We could cut that to 15 minutes and drop the
CLO2 session count ,
And I confirmed that he wants me to change from
CHGTCPA TCPKEEPALV(255)
to
CHGTCPA TCPKEEPALV(15)

My dilemma is that I can't remember why I have it set to that on this one
lpar and I am hoping that this change will not adversely affect ftp or
anything. I am going to start documenting changes to system values and
such. That being said, any concerns about this change?


Rob Berendt