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Ethernet Encapsulation and 802.3

Can someone kindly explain why 802.3 encapsulation is used for certain things, while ethernet II is showing up on some other things?

Here is what I mean. I ran ethereal and watched some traffic.

All of the CDP and STP traffic was utilizing 802.3 framing. I also noticed something called "LLC" everytime I saw the 802.3 framing method being used. What is the correlation?
http://mvpbaseball.cc/8023.jpg

Most of the other traffic was framed with Ethernet II. I noticed the "LLC" was absent completely everytime the Ethernet II framing method was used.
http://mvpbaseball.cc/e2.jpg

Thanks

ASKER CERTIFIED SOLUTION

Don Johnston

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dissolved

ASKER

Why was CDP designed to use SNAP? And why was STP designed to use 802.3? Is there any real reason or is it just because the designers of these protocols felt like doing it that way.

Also, I have been noticing I have problems with my STP protocol. When a CRC is being run on the FCS, it is coming up incorrect: (did I say that right?)

http://mvpbaseball.cc/stp.jpg

Don Johnston

My understanding is that STP being an IEEE protocol, they decided on the IEEE version of Ethernet (802.3). As for why Cisco chose the SNAP frame for CDP... Not a clue. :-)

Regrading the errors on your BPDU's, yes, that is acceptable terminology. Is it just the BPDU's that are bad?

-Don

dissolved

ASKER

What are BPDUs? Ive been noticing a lot of chesk sum errors within all differnet tyeps of paclets. Dont know whats up with that.
thanks don

Don Johnston

BPDU's are Bridge Protocol Data Units. Those are what Spanning Tree Protocol (STP) frames are called. You mentioned STP problems and CRC errors and I assumed they were related.

If you're getting checksum/CRC/FCS errors on all your frames, the first thing I would check is if they're recent. Clear your counters and check again after 5, 10 and maybe 30 minutes. If you're still getting errors, is it on all interfaces? (probably not, but it doesn't hurt to ask). If not, it's probably a bad cable or connector... or noise.

-Don