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RTTO limit as reason of teardown in msg 6-302023: what does it mean?

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Oct 4th, 2010
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The end of a "%ACE-6-302023 Teardown TCP connection ..." message is supposed to indicate the reason why the connection was torn down: TCP Fins, TCP Reset, Idle Timeout, etc. But i nour case some connections are logged with the following reason: "RTTO Limit". This reason is not documented in the "Message Guide" publication. Here's an example of a message (with masked IP adresses):

Sep 30 08:19:41 ADMCTX %ACE-6-302023: Teardown TCP connection 0x27d451 for vlan2120:xx.yy.180.17/49371 (xx.yy.180.17/1148) to vlan1562:aa.bb.6.162/443 ( duration 0:00:41 bytes 127826 RTTO Limit

So my question is: what does "RTTO Limit" mean as a reason to terminate a connection?

We are using an ACE-20 module and this message has appeared with both versions A2(2.4) and A2(3.2).



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litrenta Mon, 10/04/2010 - 13:38
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this is failure due to expiration of retransmission time an d retra

nsmission cout.

the count is detremined by syn-retry count set in connection parameter map default is 4 so

ace sends packet (1)

does not get ack in 3 seconds

ace retransmits (2)

no ack for 6 seconds

ace retransmits (3)

no ack in 12 seconds

ace retransmits (4)

no ack in 24 seconds

rtto failure

If the first 9-12 response packet from the ACE to the 
client is dropped, then as expected after the RTO(after 3 
seconds), ACE starts to retransmit the first packet to the client. If 
the client won't ACK this packet also, then ACE retransmit this 
packet at an exponentially interval(like 6, 12, 24 and 48 seconds) 
for the "syn-retry" count times, and closes the connection by 
sending a RST.


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