Subject: Re: Carry IP Packet in Ethernet Frame in IEEE 802.3 LLC EncapsulationFormat

From: Atul_Gharde <[email-masked]>
Date: Wed, 1 Aug 2001 19:57:45 +0530 (IST)

hi,
  this mail is in continuation of the thread started by Steinar Haug in
which he wrote that he hadn't ever seen or heard of any product use 802.3
LLC frame format to carry IP Packet in.
   i am confused . what did he mean to say ?
 Did he mean to say that all the recent implementations of carrying IP
packets in ethernet frame (DIX or 802.3 ?? ) don't use LLC at all. can
anybody specify the exact frame format ? 
 thanking in advance,

atul

---

From: [email-masked]
Date: Wed, 01 Aug 2001 18:33:03 +0200

> LLC frame format to carry IP Packet in.

You're digging up a rather old thread, but okay. I don't believe I said
what you claim here, I *did* say on 30. March 2000:

| > I never see or heard any product use 802.3 LLC frame format to carry IP
| > packet. But I am not sure I am correct. Does anyone knows that some product
| > does use the LLC frame to carry IP packets and why?
|
| Older HP-UX (300 & 400 series) systems could do this.

Notice I said that older HP-UX systems could do this. Thinking back (my
memory is a bit hazy here), I believe they actually could use *SNAP*
encapsulation, but not pure LLC.

> anybody specify the exact frame format ? 

As far as I know, all recent IP implementations use Ethertype 0x0800 to
carry IP. No SNAP or LLC. Thus you have a 14 byte Ethernet header (which
includes a 2 byte type field) and then up to 1500 bytes of IP, followed
by the Ethernet CRC.

Note that you could argue that Cisco ISL encapsulation uses the 802.3
LLC frame format - and in that case, there's a lot of IP in LLC traffic
today :-)

Note also that having a type field in bytes 13 and 14 of the Ethernet
frame is now an official part of 802.3.

Steinar Haug, Nethelp consulting, [email-masked]