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RE: Ethernet Frame Types. [7:60071] posted 01/01/2003
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once again, many thx Priscilla - thats great.

-----Original Message-----
From: Priscilla Oppenheimer [mailto:nobody@xxxxxxxxxxxxxx]
Sent: 01 January 2003 21:05
To: cisco@xxxxxxxxxxxxxx
Subject: RE: Ethernet Frame Types. [7:60071]


Ken.Farrington@xxxxxxxxxxxxxxxxxxx wrote:
> 
> Hello again,
> 
> Is it possible to run any other encapsulation of Ethernet on a
> Cisco
> interface other than ARPA (Ethernet_II).

With IPX, it is possible to change the Ethernet frame type. IPX supports
four different frame types. Check this out:

Albany(config)#int e0
Albany(config-if)#ipx network 400 encapsulation ?
  arpa          Novell Ethernet_II
  hdlc          HDLC on serial links
  novell-ether  Novell Ethernet_802.3
  sap           IEEE 802.2 on Ethernet, FDDI, Token Ring
  snap          IEEE 802.2 SNAP on Ethernet, Token Ring, and FDDI

AppleTalk Ph. 2 doesn't use Ethernet II either, but it's not configurable.
It uses 802.3 with 802.2 and SNAP.

A few other protocols automatically don't use Ethernet II either, such as
CDP, BPDU, NetBEUI, and IS-IS.

Of course, if you're using VLANs, you can change the Ethernet encapsulation
to 802.1q or ISL, but the "real" Ethernet frame is still Ethernet II if
you're using IP.

If your concern is IP, then 99.999999% of IP implementations use Ethernet
II. Cisco always defaults to that. If, however, a Cisco router sees a data
stream from a host where IP uses 802.3 with 802.2, the router can handle
this. In order to make it work, you need to use the obscure "arp snap"
command. So, although you can't configure IP to use anything other than
Ethernet II, you can configure ARP to use SNAP for that 0.0000001% of cases
where a host is doing IP on top of 802.3 with 802.2.

You might enjoy my Ethernet lab scenario here:

http://www.troubleshootingnetworks.com/ethernet.html

Priscilla

> 
> Many thx
> 
> 
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