[e2e] Ethernet Encapsulation

[Tianbo Kuang]

Hi,

Craig Partridge wrote:

> In message <3BEAE744.B9C0CD03 at cpsc.ucalgary.ca>, Tianbo Kuang writes:
>
> >> So, if the length
> >> supplied by the link layer is is too short, the packet
> >> should be discarded.  If it is longer, the excess data is
> >> simply ignored.
> >
> >I thought the packets handed to IP layer by link layer are "clean" as the MAC
> >layer has CRC. The situation you mentioned can only be caused by an error of
> >higher layers. Am I wrong?
>
> I believe Ethernet specs used to permit padding to 16-bit boundaries.
> In general, link layers are permitted to pad (and, for instance, ATM does)

> Truncation indicates an error somewhere in the transmission path
> (not necessarily a higher layer -- it may have been a previous network
> hop, or even an bug in the sending or receiving Ethernet hardware).
> [I can't think of a case where truncation is not caused by error but
> others may remember odd cases]

So because Ethernet frame does not have a length field, the link layer has to
hand the padded frame to IP layer after ripping off the header and crc? What
about the ieee 802.3 who has a length field? Will it get rid of the padding by
itself?

--Tianbo