Giant Frame Errors

We have a Cisco 6509 IOS 12.2(17a)SX1 which has an interface (supervisor 720 card) which reports a large number of Giant Frame errors. We have tried setting the MTU size on the interface to 9126 but the Giant Frame errors persist at an alarming rate (1 in 10). Link is routed point to point link (ie not just switching over it) only doing ip traffic. There does not seem to be any noticeable impact on the network but I would like to find out what is causing the Giant Frames and how if at all we can stop them occurring. Any help/advice appreciated.

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How is the system on the other end configured?
You may want to try a sniffer to see what the packets actually look like. When we have network issues I use ethereal on a regular basis to see what is actually happening. Even though I’m not trained on this software, it has pointed me to a number of problems that would have been much harder to find via my other resources.

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  • Nazman
    We tried using Observer to sniff the traffic but I don't think it allowed us to see the Giant Frames as they were dropped or the nic on the laptop did not support it with Observer sniffer. May try ethereal but can't see it being any different.
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  • Astronomer
    I only know one person who has done sniffing on serial links. I sent David a question about this. I will have to wait to see if there is a response. In the meantime, I recommend you look at the configuration of the system sending the giant frames. rt
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  • Edwardzeng
    The Catalyst 6000 series and 7600 Optical Services Router (OSR) platform can support jumbo frame sizes as of release 6.1(1) of CatOS, and 12.1(1)E for Native IOS. However, this is dependent on the type of line cards that you use. There are generally no restrictions to enable the jumbo frame size feature. You can use this feature with trunking/non-trunking and channeling/non-channeling. The default MTU size is 9216 bytes after you enable jumbo frame support on the individual port. However, an Application Specific Integrated Circuit (ASIC) limitation requires that you limit the MTU size to 8092 bytes on these 10/100-based line cards
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