See my comments below...... At 09:37 AM 1/4/02, bergenpeak wrote: >Question from Chappel's book (ICRC, Chapter 11, page 269). Is >generic as well. About IPX framing options. ICRC shows four >different ways to frame IPX on ethernet: > >Cisco name frame format >----- ----- >novell-ether 802.3 IPX >sap 802.3 802.2_LLC IPX >arpa ethernet IPX >snap 802.3 802.2_LLC SNAP IPX > >I understand "arpa" format to be where "ethernet" format >is where the 2 bytes following the SRC MAC is a type field. > >"sap" and "snap" format is where these 2 bytes are a length field >and are minimally followed by an 802.2 LLC. > >My question is about the "novell-ether" format. This format >shows an 802.3 "header" but no field for a type value.
Yes, that is correct. Novell started shipping their network operating system before it was clear that 802.3 should be used with 802.2. Some people claim that Novell was suffering from grandiosity and figured there was no need to identify the next layer because it would always be IPX. (Novell did almost corner the client/server market). I think they just either made a genuine mistake or had a different view of how it would work. They figured the packet would go to the network operating system which could then figure out if the packet was for it or for some other protocol, such as IP. > Is >this correct that there is no explicit type field in the >"novell-ether" format? It's true! >Is the DST MAC used to identify this as >a Novel frame, and hence no type field is necessary? No, it's not the DST MAC that is used. Luckily the first two bytes of an IPX header are almost always 0xFFFF. That's the IPX checksum, which Novell didn't use. So routers, Sniffers, and other applications can rather easily recognize a Novell-Ether frame. When using this frame format, you cannot use the IPX checksum feature. The frame format is slowly disappearing and with the newer frame formats, you can use the IPX checksum. And this is the truth. (Many books get this wrong. You can trust Laura Chappell on this though. She's a Novell guru.) Priscilla >Thanks ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30962&t=30921 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
