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New Member

a packet loss in Cisco3662 with using category5 cable.

hi, i'm a network engineer in japanese mobile phone company.

this week, we tested the throughput in cisco3662. we tested for 72hours with 50Kpps. we had one packet loss in 9 billion packets input/output. we consider cisco3662 itself has no problem. so, there may be a problem in the category 5 cable. is there any limitation in the category5 cable? does category 5 cable cause the packet loss?? i checked ieee802.3 CSMA/CD, but couldn't find any reference of the limitation. i really appreciate if anybody knows anything about this... thank you.

4 REPLIES
New Member

Re: a packet loss in Cisco3662 with using category5 cable.

All kinds of external interferance can cause a packet to get lost, even switching on the light can cause this. It is quite normal and normaly gets resolved by higher layer error correction. 1 in 9 billion is actualy very good.

Green

Re: a packet loss in Cisco3662 with using category5 cable.

Any fault in the cable would not show as a loss, it would show up as excessive re-transmissions. The higher-level protocols should recognize the dropped/lost frame and re-transmit.

A lost or dropped packet (L3) or frame (L2) could occur anywhere from the cable up to the internal buffering of the device, but the higher-level processes should identify the "gap" and ask for a re-send (or get a negative acknowledgement from the other end and do the re-transmit).

Bad (kinked, twisted, not meeting minimum bend radius, crushed jacket, bad termination ...) cables would show symptoms of high-speed intolerance (many re-transmits at 100 mbps, fewer or none at 10mbps).

Were there any other elevated parameters?

Scott

New Member

Re: a packet loss in Cisco3662 with using category5 cable.

thank you for answering my question.

i guess there is no limitation in ethernet cable.

there were also 130 output queue drops in the interface i tested.

one input drops and 130 output queue drops.

does this mean buffer got full??

Green

Re: a packet loss in Cisco3662 with using category5 cable.

More than likely, the buffer was full. Usually, that would mean that the system connected to that port was too slow (or too busy) to handle the traffic.

130 drops may or may not be a big deal, depending on what share of the traffic "130" represents. If it dropped 130 out of 1300 ... that's a big deal. If it dropped 130 out of 130 BILLION .... it's nothing to worry about.

Assuming that 130 is "too much:"

If that port connect so a server, you may want to investigate some upgrades / updates / enhancements to that server (i.e., better / faster NICS, better / more efficient OS, additional NICS ala Fast EtherChannel, etc0.

If that link goes to another switch, there may be something wrong with the other switch, or it's seriously oversubscribed or being bombarded with broadcasts / multicasts.

If that port goes to a router (and then out to the WAN), then there's not much else you can do aside from the usual recommendations: Reduce your WAN traffic to a minimum (efficient routing protocols or static routes), establish some QOS for the vital traffic, and monitor the WAN link closely to see where the bandwidth goes....then adjust things as necessary.

If that port goes to a router that is predominantly an inter-VLAN or internal subnet-subnet router (i.e., most or all high speed interfaces), then look at your processor load, review your Access-Lists and routing tables ....anything you can do to improve the efficiency is likely to help.

Good Luck

Scott

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