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Hi! I’m evaluating the opportunity to develop a small packet filtering components for Windows 95/98 due to some custom requirements on the basif of that I need to use very limited hardware resources.
It seems that Packet Filter driver is not able to correctly understand packets that are biggers than 1400 bytes.
Do you think that is possible this misfunctions ?
Thank you in advance for your support.
Gianandrea
It seems that Packet Filter driver is not able to correctly understand packets that are biggers than 1400 bytes.
Well, Ethernet packets can be up to 1514 bytes length and these packets can be processed by WinpkFilter even if they are of maximum size. What exactly problems have you met with processing large packets?
My trouble is related to manage udp traffic generated from a custom application that uses packet with size limit at 7900 byte. This type of traffic is not correctly received from packet filter driver, that is not able to understand source and destination port. So, it’s not possible to correctly manage this traffic.
I’ve seen that the value of 1514 bytes is indicated in the .H library. Do you think that is possible to change this value ? Which value do you suggest me? I’ve seen that packets are correctly managed also in the case that the size of packets is lightly bigger than 1514 bytes (my tests tell me that all is correctly done with a size up to 1573 bytes. Over this value the packet is not correctly received.
Thank you in advance for your support.
Gianandrea
1514 bytes is a network media limit for 802.3 Ethernet (actually it is 1518 bytes but two extra bytes exist only on the physical media and not visible by software). 14 bytes are used for Ethernet header, so maximum IP MTU is 1500 bytes. All IP packets above this size are fragmented by TCP/IP stack. In your case 7900 bytes UDP packet will be fragmented to 6 IP packets and only first fragment will contain UDP header. You can reconstruct the packet from fragments received from WinpkFilter driver if you need to do so.
Some modern network cards (Gigabit Ethernet) may support frames larger than 1514 bytes (9000 bytes “jumbo frames”). WinpkFilter driver can be extended to work with these larger frames (default on site build does not support them and limits MTU to normal 1514 bytes), but I don’t think this is your case, correct me if I’m wrong.
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