Physical and Data Link Layers - Frame Encapsulation

By Dan DiNicolo, June 2nd, 2006 Posted in CCNA Study Guide Chapter 04. Subscribe to our RSS Feed

NetWare protocols can run over a variety of different network technologies, similar to TCP/IP. For the purpose of keeping things simple, in this section we’ll concentrate on Ethernet. However, IPX can also be run over Token Ring, FDDI, ATM and a variety of WAN technologies. If you recall, Novell originally defined the 802.3 frame type to be used over Ethernet networks. These frames lacked a Type field, since all 802.3 frames were assumed to be destined for IPX at the Network layer. The 802.3 frame type is commonly referred to as Novell Ethernet 802.3 or Ethernet Raw. Different versions of NetWare use different Ethernet frame types as their default for encapsulating IPX packets. In NetWare 3.11 and earlier versions, the default frame type was 802.3. Beginning with Netware 3.12, the default frame type was changed to 802.2.

This presents a technical challenge, since different frame types are not interoperable. As such, a system configured to use only 802.3 frames cannot communicate with a system in the same broadcast domain that uses only 802.2 frames.

To help overcome these limitations, a Cisco router can be configured to use more than one Ethernet encapsulation type for IPX on a single interface. This allows a router to communicate with systems using different frame types. We’ll look at the actual configuration of IPX on a router in Chapter 8. For now, it is sufficient to know the different frame types support by Cisco, and the terms used to describe them.

• novell-ether. Refers to 802.3 frames that lack an LLC header.
• sap. Refers to the IEEE standard Ethernet frame with an 802.2 LLC header.
• arpa. Refers to the Ethernet II frame type.
• snap. Refers to the Ethernet SNAP frame type.

Written by Dan DiNicolo - Visit Website

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