On Fri, Nov 28, 2003 at 07:47:10AM -0800, john g wrote:
> question about Layer 2 info displayed in ethereal
>
> difference between "IEEE 802.3" and "Ethernet II" ?
"IEEE 802.3" refers to packets in which the type/length field is a
length field; "Ethernet II" refers to packets in which the type/length
field is a type field.
> since i am capturing frames on a 10/100 ethernet the
> layer 2 info should have been "IEEE 802.3",
No. Whether a packet is shown as "IEEE 802.3" or "Ethernet II" doesn't
depend on the type of network you're capturing on; it depends on the way
the packet is encapsulated.
Given that IEEE Std 802.3 describes both the original "Ethernet II"
(DEC/Intel/Xerox, or "DIX", Ethernet, which I assume is called "Ethernet
II" because it was the successor to the 3Mb experimental Ethernet from
Xerox, which I think had 8-bit rather than 48-bit link-layer addresses)
encapsulation, with no length field in the packet, and the 802.x
encapsulation, with a length field (requiring an 802.2 LLC header except
for various unusual encapsulations such as Novell's raw 802.3
encapsulation of IPX), perhaps "IEEE 802.3" isn't the best term for the
length-field version of Ethernet packets; however, I don't know of any
better names.
> it is commonly understood that ethernet 10/100 is ieee
> 802.3 ? is that correct ?
There are IEEE 802.3 standards for 10Mb, 100Mb, 1000Mb, and 10000Mb
Ethernet, so, in that sense, 10Mb and 100Mb Ethernet are IEEE 802.3.
> only for some common cisco protocols like cdp packets
> the layer 2 shows up as ieee 802.3 ?
Cisco didn't get Ethernet type values for their protocols such as CDP;
instead, they used one of their own OUIs, and their own protocol
numbers, for those protocols. Therefore, on Ethernet, they're
encapsulated with length-field 802.3 headers plus an 802.2 header with
SNAP.
