tcp keepalives

[teyobanilom]

I am not sure if "service tcp-keepalives-in" generates TCP keepalives for TCP sessions "to" this router anad "service tcp-keepalives-out" commands generates TCP keepalives for TCP session "from" this router.

Is this correct?

Secondly, if I execute the command on an production router, will it apply to already active TCP session or to new TCP sessions?

If it does not apply to already active TCP session, is there a way to reset an active connection besides totally re-starting the TCP session?

I have a RAS with remote users and some TCP session gets hang. I am aware of the of exec-timeout command. I am just exploring all posibilities to clear out a hung session.

Thanks all,

Boyet

[Richard Burts]

the documentation is pretty clear that keepalive-in applies to connection from some external device to the router and keepalive-out applies to connections from the router to some external device.

I use these commands on most of the routers that I configure and believe that they are very useful.

I do not know for sure if they apply to already active connections. If I were going to guess I would guess that they probably do get applied to already active sessions. And if you go ahead and configure it on your router and leave it in place then the question of already active sessions becomes a moot question. I know of no reason to remove them once configured.

HTH

Rick

[teyobanilom]

I was just hoping that I do not need to manually clear each hung TCP session if the command applies to already active sessions.

I was just wondering though how much network overhead does it introduce? I notice the Cisco keepalives are sent every 60 secs for an idle TCP session. I read somewhere that it is suppose to be 2 hours. Is there a way to control the frequency?

Thanks.

[teyobanilom]

Firstly, does anybody know how many keepalive is missed before the TCP session is cleared?

Secondly, what is the keepalive timer?

Thanks

[Richard Burts]

According to this documentation the keepalives are sent every minute and if 5 minutes goes by with no response the connection is broken down:

Set Up the TCP Keepalive Packet Service

The TCP keepalive capability allows a router to detect when the host with which it is communicating experiences a system failure, even if data stops being transmitted (in either direction). This is most useful on incoming connections. For example, if a host failure occurs while talking to a printer, the router might never notice, because the printer does not generate any traffic in the opposite direction. If keepalives are enabled, they are sent once every minute on otherwise idle connections. If five minutes pass and no keepalives are detected, the connection is closed. The connection is also closed if the host replies to a keepalive packet with a reset packet. This will happen if the host crashes and comes back up again.

Here is the URL:http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1826/products_configuration_guide_chapter09186a00800d9b68.html

HTH

Rick