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can't keep the "show flows" up

Answered Question

When I telnet to vip with the specific port number. The "show flows" only can see it retains for 5 minutes. But I still see the connection is established on the servers. Is this someting relating the application software problem ? Because I have other application software, which works very similiar . When the connection is not displating in the "show flows", Is this meaning the connection dropping ? Please advise. Thanks in advance.


Wil


Correct Answer by Gilles Dufour about 14 years 5 months ago

Wil,


I'll try to keep it simple.

A flow is describes by a FCB (Flow Control Block).

The 'show flow' commands describe the info inside the FCBs


When a flow is idle for a predefine period of time (like 16 seconds for TCP), the

FCB is marked as reusable.

So at any given time the FCB info can be erased and replaced with new info.

The CSS can still use the FCB marked as reusable until its content is erased.


So, your connection could still be alive but the FCB has been marked to be reused and therefore you will end up losing the connection.

The 'show flow' only display the FCB that have not been marked as reusable.


The solution would be to increase the frequency of your heartbeat or use one of the command to increase the timeout on the CSS.


flow port

flow permanent


Gilles.

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Gilles Dufour Wed, 03/12/2003 - 08:27
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do you have any traffic going through the connection ?

If not, than the CSS will most probably timeout the connection and mark it for being reusable.

Once the flow disappears, if you type something in the telnet session, does it close the connection, does it send the data to the server, ... ?


You might want to use a sniffer to capture the full connection from start to end.


Gilles.

Gilles

Thank you for the respone. When the "show flows" disappears the telent session is still OK. We are sending the heart bit very 30 seconds. I guess my question is when "show flows" disappears, is that meaning the connection is cut ? If I extend the keepalive time, will it resolved the problems ? Thanks


-Wil

Correct Answer
Gilles Dufour Thu, 03/13/2003 - 03:53
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  • Cisco Employee,

Wil,


I'll try to keep it simple.

A flow is describes by a FCB (Flow Control Block).

The 'show flow' commands describe the info inside the FCBs


When a flow is idle for a predefine period of time (like 16 seconds for TCP), the

FCB is marked as reusable.

So at any given time the FCB info can be erased and replaced with new info.

The CSS can still use the FCB marked as reusable until its content is erased.


So, your connection could still be alive but the FCB has been marked to be reused and therefore you will end up losing the connection.

The 'show flow' only display the FCB that have not been marked as reusable.


The solution would be to increase the frequency of your heartbeat or use one of the command to increase the timeout on the CSS.


flow port

flow permanent


Gilles.

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