Pings dropping out, but I see a repeating pattern

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Jun 6th, 2008
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Good Morning. I hope someone can help me because I am at my wits ends.

On one of my WAN links I am experiencing a most unusual problem.


The campus is served by a Cisco router and a T1 that accesses the internet through my NOC just fine. However when they try to access my DMZ, they get timeouts. When doing ping testing, I find that the end users in that bldg can ping one particular IP on my ME 6524 (which was only installed 3 weeks ago) and will get exactly 59-60 successful replies followed by exactly 11 dropped replies, then it repeats. Meanwhile the entire time they are pinging www.yahoo.com cleanly.


Now both the connections to our DMZ and to the internet for this location route through our ME6524... it is just that there are two different IPs for the two different routes.


To make matters more interesting, when I ping the "problem" address from the inside interface of the router at the location in question I have no problems. As soon as I hook up something to the inside interface and then try the same ping test from that device (I used a laptop and crossover cable).. I get the 60 good pings replies followed by 11 drops.


I tried replacing the router. I also rebooted all equipment along the path.


I just don't know what else to do.

I shouldn't see a pattern to the dropouts.


Thank You,

Joe


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blubericisco Fri, 06/06/2008 - 06:10
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Have you checked for an IP address conflict for the "problem" address?


From the laptop, you could check your ARP table for the MAC address of the IP when it works, and check it again when it doesn't work. If the MAC changes when it doesn't work, then there's a conflict somewhere.

aijaz802 Fri, 06/06/2008 - 22:19
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Hi,


There might be speed/duplex mismatch. Please recheck and fix the speed/duplex settings on both ends.


Regards,

cisco_lad2004 Sun, 06/08/2008 - 08:46
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I have just skimed thru ur post, so apologies if I am out of synch.


If the drop rate is consistent, there could be protection somewhere in the path. Watch out for QOS policing dropping ICMP packets.


HTH


Sam

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