ixp4xx IAL3.0 how to increase ethernet Rx maximum frame size

ixp4xx IAL3.0 how to increase ethernet Rx maximum frame size


I'm currently using IXP400 Intel Access Library version 3.0. How can I increase the ethernet Rx maximum frame size? Any help would be greatly appreciated.


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I had a look at the statistics collected by Intel Access Library and found that RxLargeFramesDiscards increases whenever I send it a large packet. My ethernet configuration is a little unusual as I have a switch connected to my ethernet port and the switch adds 4 bytes of frame header data to each ethernet packet.

I spend some time looking into Intel Access Library source code and found that the NPE is keeping count of the RxLargeFramesDiscards, which leads me to think the NPE is doing comparison of incoming packet size with a defined maximum size. Is it possible to increase the maximum size?

I have this same ethernet configuration (with 4 bytes added to ethernet frame) working with Intel Access Library version 2.4.


In the Intel ethernet driver, I added a line of code to call this function ixEthAccFilteringPortMaximumFrameSizeSet and set the frame size to some bigger number and that seem to fixed the dropping of large frames problem.

The question I have now is, what does this function actually do? Does the function change the maximum Tx frame size as well? I noticed there's ixEthAccFilteringPortMaximumRxFrameSizeSet and ixEthAccFilteringPortMaximumTxFrameSizeSet. Calling the Rx version seem to limit the NPE to accepting 64 bytes frames only. What's the difference between these 3 functions?


Hi JA,

some answersfor your questions.

ixEthAccFilteringPortMaximumFrameSizeSet() is a new function call in CSR3.0 which is the same function as ixEthDBFilteringPortMaximumFrameSizeSet() in CSR2.4.

Please refer to CSR 3.0 programming guide section Frame Size Filtering.

The maximum supported Ethernet frame size is 16,320 bytes. This value is set on a per-port basis using the IxEthAcc API. The maximum frame size for fast path support is only 1518.

Jason Zhu

if you have further questions about Intel IXP products, you can submit your questions here:


Which product selection should one chose when submitting a question ?
The ixp4xx CPU family is not listed.



For the IXPxxxx product line, you need to contract your local distributor to help you with submitting your questions for support.



Hello Thai,

I don't mean to be disrespectful, but Intel local distributors are hopeless. They're not able to help me on any of my problems, which is disappointing. Is there better support available? Maybe IXP4XX Intel Access Library engineers mailing list that I can subscribe to?


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