Delay in Ping reply

Unanswered Question
Jun 11th, 2010
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Hi All,

I have 2 Cisco 2811 routers which are connected back to back through 2 modems. In order to understand the time taken for the interface to come up, cable connected to Serial interface has been removed and plugged in again.

I have kept continuous ping from the LAN side of one router to the LAN side of remote router.

Observations of this testing are as follows:

If I plugin the cable to serial interface within 30 seconds of removal of cable, ping gets reply within 3 seconds of delay.

If I plugin the calbe to serial interface after spending 1 minute or more, the ping reply gets delayed by 35 to 40 seconds.

Please help me to understand the cause.

Thank you,

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bgandhi Fri, 06/11/2010 - 00:58
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Please explain in detail what are you trying to acheive.



nagabhushana.k Fri, 06/11/2010 - 02:38
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Hi Bhavesh,

Thank you very much for your reply.

My intention is to minimise the delay after reconnection regardless of time spent before reconnecting the cable, in other words, to minimize the delay of getting a reply or making the link up at minimal amount of time.

Let me elaborate a little bit more.

Case 1: I disconnect the cable and plug it back again within 30 seconds of disconnection. Within 3 to 4 seconds after reconnection, reply for ping starts from remote end.

Case 2: I disconnect the cable and plug it back after spending 1 or more minute. Now, I observe there is delay of 35 to 40 seconds after reconnection, before reply starts from remote end. Is it possible to reduce this time delay to minimal amount.


bgandhi Fri, 06/11/2010 - 03:00
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In both cases, you need to focus on following things.

1.) Keepalive times of interface - This would determine the duration for updating routing protocol and table to update

2.) Routing protocol timers -  This would determine convergence time.

Please tweak them to acheive desired results. However, both of them would impct router CPU if set very low.




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