packet loss

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Dec 10th, 2007
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We just installed a new circuit from the telco and we are noticing packet loss whenever we do a stress test. (ping x.x.x.x source x.x.x.x repeat 3000 size 1500 data 0000). We are seeing about 5-8 packet being lost. Telco troubleshooted and made a change to the incoming cables from 2 wire to 4 wires. As per them they are not seeing any errors when tested anymore. We replaced the cables, and card on the router, and checked the DSU.

What we did notice if we input a mtu size of 1490 on the config the test is fine, however configuring mtu size is not company standard. We also have other sites with similar config as well as router model and they are fine. According to telco they are not aware of any mtu setting on their end, therefore they cannot make a change related to mtu.

For now we don't want to break company standard and configure mtu size, but as far as testing and obtaining no packet loss this is the only thing we could come up with that's giving us favourable results.

Any ideas on this little dilema would be greatly appreciated.


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cisco_lad2004 Mon, 12/10/2007 - 08:49
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on ur test path, clear counters, ping with and then do "sh interfaces te2/1 counters errors" and take a look at error types (specially "Giants").

I dont know how much bandwidth u have purchased, but take a look at interface load is case lines is maxed out.

check your CPU while testing.

Sam Thinking out loud :-)

1-If MTU mistmatch was an issue, you would have lost all packets.

2-If CoPP was configured by ur provider, you would have lost packets with small or large MTU.

3-ask provider to confirm MTU size at their end ( increasing it is not a problem).



kimrajsohan Mon, 12/10/2007 - 10:29
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I've attached a copy of the sh int command, cleared the counters etc, cpu seems to be ok. The bandwidth is a T1 sub rated to 128k.

according to the telco there is nothing for them to check/change relating to MTU size. We thought the DSU had a mtu setting but they said no. So far the only setting we can make is on the CE router.

this one is puzzling

cisco_lad2004 Mon, 12/10/2007 - 10:38
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have tested after this input?

Apart from 7 interface resets, all looks ok.

are u using MPLS? if so, you will require more than 1500Byte MTU due to label imposition.



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