Thanks very much, cause I had the impression I hadn't understood anything
from my readings.
Best Regards,
Douglas
>>Great answer, but be careful with that "raw" term which to Novell people
>means the Ethernet raw format, aka ETHERNET_802.3, ask novell-ether, which
>is dest, src, length, immediately followed by the IPX header. The frame is
>only recognizable because an IPX header starts with an XNS checksum, which
>is FFFF. Novell didn't actually use the checksum when they borrowed XNS to
>create IPX.
>
>A "real" 802.3 frame has dest, src, length and an 802.2 header with DSAP
>and SSAP and maybe SNAP following. An Ethernet II frame has dest, src, type.
>
>Priscilla
>
>At 11:26 PM 5/25/01, R. Benjamin Kessler wrote:
>>Just getting started, there are probably some "easier" reads out there but
>>that book will definitely give you the goods on TCP/IP...
>>
>>Regarding your question/statement, you are accurate that the "raw" Ethernet
>>frame format has DA, SA, EtherType, Data, and FCS - to be a valid frame it
>>just has to be between 64 and 1518 bytes (if we're including the 4 bytes of
>>the FCS in our calculations) - notice that the top end number is not 1500 -
>>the common "max" MTU size for Ethernet-attached devices talking IP. MTU is
>>a function of L3, not L2.
>>
>>The IP header will indicate how many bytes of the Ethernet payload is
>>consumed by IP "stuff" - add this to the 14 bytes consumed by the
>>destination address (6), source address (6) and ethertype (2) to get the
>>total frame size (+ plus the trailing 4 bytes for the FCS). This statement
>>will be true unless adding all that up equals a number less than 60 (64
>>w/FCS) in which case the packet will be "padded" with 0's to make it a
legal
>>Ethernet packet.
>>
>>I think it is generally considered a good thing that packets aren't padded
>>to the full Ethernet size (or MTU) - it that were the spec, I'm thinking
>>that ATM would be a lot more popular as a LAN medium.
>>
>>Hope this helps.
>>
>>Ben
>>
>>
>>
>>-----Original Message-----
>>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
>>[EMAIL PROTECTED]
>>Sent: Friday, May 25, 2001 6:59 PM
>>To: [EMAIL PROTECTED]
>>Subject: Ethernet frame format [7:5996]
>>
>>
>>Dear Members List,
>>
>>I've just started the track for CCNA and, following all the repeated
advices
>>posted in this list, I started studing for Internetworking with TCP/IP, by
>>Douglas Comer.
>>
>>The ethernet frame format stablishes as necessary information for the frame
>>as DA, SA, Type, Data Area(variable from 46 to 1500 bytes) and a trailer
FCS
>>4 bytes.
>>
>>I don't see how can we have different frame sizes correctly received, since
>>there is no information about the specific lenght for every single frame,
>>taking in account the asynchrounous nature of this communication.
>>
>>I thought that the layer 3 would pad till the MTU was reached, but I saw a
>>trace on an ethernet network and I could see different frame sizes.
>>
>>Thanks in advance,
>>
>>Douglas Baltazar de Queiroz - Field Enginner
>>
>>---
>>UOL: o melhor da Internet.
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>FAQ, list archives, and subscription info:
http://www.groupstudy.com/list/cisco.html
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>
---
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