Cisco 2651 router

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Feb 29th, 2008
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I have a Cisco 2651 router running IOS 12.2(10r)1. I'm trying to determine if there is a bottleneck at the router itself or on my local segment. Are there are utilites on the router or out there to easily troubleshoot the problem?

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Edison Ortiz Fri, 02/29/2008 - 21:45
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As the packets come into the router, you will have values under the interface such as packets input and input bytes.


This value must match or the value must be very close to the packets output and output bytes on the exiting interface.


If the packets are very close in value, then the router is forwarding the traffic as it's received and you don't have a bottleneck at the router.



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Sean McCoy Mon, 03/03/2008 - 05:50
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Edison-


Can I view both the packet input, input bytes, packet output and output bytes through an IOS command?


Sean

Edison Ortiz Mon, 03/03/2008 - 06:13
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Yes, the command is show interface


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Sean McCoy Mon, 03/03/2008 - 06:35
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Edison-


Do these seem like normal numbers?


271753779 packets input, 7005960250 cells, 329527459615 bytes

194194777 packets output, 1334663195 cells, 62280919022 bytes



Joseph W. Doherty Sat, 03/01/2008 - 11:17
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You didn't describe whether your using the 2651 for pure LAN routing or whether it's a WAN router.


The distinction can be important because often the software based routers can be overloaded with heavy LAN-to-LAN traffic. An easy thing to also check is whether the CPU is often very high. (The in/out counters Edison suggests looking at will tell if packets are being lost within the router.)


Something else easy to check are error counters on the interfaces. Most should be zero or very low.


As a WAN router, often bottlenecks form as typical LAN bandwidth is reduced to typical WAN bandwidth. An easy thing to check is whether you see a high percentage of "output drops". Ideally, you also need to see the "output drops" on the device providing traffic to your router to easily determine whether you have an inbound bottleneck.


The above is not all inclusive but might quickly and easily identify some of the more common performance trouble areas that can be identified looking at router stats.

Sean McCoy Mon, 03/03/2008 - 05:47
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Joseph-


The 2651 in my environment is a LAN router. The serial side of the router is an ATM interface which connects to a PTP back to a 7206VXR at my main site. How would I monitor (or view)the output drops? Thanks for your response.


Sean

Joseph W. Doherty Mon, 03/03/2008 - 16:04
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Output drops should be visible as one of the counters when you issue a show interface.


If you're using ATM, insure your ATM settings truly agree with the link's configuration if using something like VBR. If they don't, and you're faster, the provider can drop ATM cells which in turn will result in lost of packets. This one can be a bit difficult to find depending where the cells are being dropped. TCP's performance will slow as it recovers lost packets. Tracking one side's output packets against the far side's input packets will show the loss. Your interface's ATM SAR might also register missing cells when it attempts to reconstruct the packet.


The 2651 is quite capable for dealing with the bandwidth of the WAN circuits you're likely to attach to it. (I.e. it's fine for LAN to WAN or the converse.) It can lack performance for higher speed (e.g. 100 Mbps) LAN to LAN routing.

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