Cell Relay Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: Ethertype in ATM Driver
In article <32B6F091.6B41@tid.es> David Castells i Rufas <dcr@tid.es> writes: > Now I am working with the Ethernet maximum packet size (MTU), which is > 1536. > All the documentation I have read indicate to use a MTU size of 9180. > If I used this MTU I could get a packet of 0x0806 bytes and therefore I > wouldn't be able to determine wether the packet was a ARP message or an > IP packet of length 0x0806. Since RFC1577 uses LLC/SNAP encapsulation, if you receive a packet over the network with 0x0806 in its length field it is most certainly an IP (or some other packet) of length 0x0806. All packets will start with 0xAAAA03 followed by the 5-byte SNAP. This 5-byte SNAP is 0x0000000800 for IP and 0x0000000806 for ARP. So you can always distiguish between IP and ARP. In other direction things may be more tricky. I don't know much about how NT's IP and ARP layers bind to drivers. Do they bind using "ethertypes"? If this is the case then a packet with 0x0806 in the length field is probably an ARP packet and can not be a packet of length 0x0806. The only way you will know the length of the packet is through the actual length of the data buffer passed to you. ----------------------------------------------------------------------- Alagu Periyannan Internet: alagu@apple.com Communications Products & Technology Apple Computer, Inc. |
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