Cisco Systems BC-109 Enable Token Ring LLC2-to-Ethernet Conversion, Enable 0x80d5 Processing

Configure Translation between SRB and Transparent Bridging Environments

Enable Token Ring LLC2-to-Ethernet Conversion

The Cisco IOS software supports the following types of Token Ring-to-Ethernet frame conversions using Logical Link Control, type 2 (LLC2) Protocol:

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Token Ring LLC2 to Ethernet Type II (0x80d5 processing)

Token Ring LLC2 to Ethernet 802.3 LLC2 (standard)

For most non-IBM hosts, Token Ring LLC2 frames can be translated in a straightforward manner into Ethernet 802.3 LLC2 frames. This is the default conversion in the Cisco IOS software.

However, many Ethernet-attached IBM devices use nonstandard encapsulation of LLC2 on Ethernet. Such IBM devices, including PS/2s running OS/2 Extended Edition and RT-PCs, do not place their LLC2 data inside an 802.3 format frame, but rather place it into an Ethernet Type 2 frame whose type is specified as 0x80d5. This nonstandard format is called 0x80d5, named after the type of frame. This format is also sometimes called RT-PC Ethernet format because these frames were first widely seen on the RT-PC. Hosts using this nonstandard 0x80d5 format cannot read the standard Token Ring LLC2 to Ethernet 802.2 LLC frames.

To enable Token Ring LLC2 to Ethernet LLC2 conversion, you can perform one or both of the following tasks:

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Enable 0x80d5 Processing

Enable Standard Token Ring LLC2-to-Ethernet LLC2 Conversion

Enable 0x80d5 Processing

You can change the Cisco IOS software’s default translation behavior of translating Token Ring LLC to Ethernet 802.3 LLC to translate Token Ring LLC2 frames into Ethernet 0x80d5 format frames. To enable this nonstandard conversion, use the following command in global configuration mode:

Command	Purpose
source-bridge enable-80d5	Change the Ethernet/Token Ring translation behavior to translate Token
	Ring LLC2 frames into Ethernet 0x80d5 format frames.

Enable Standard Token Ring LLC2-to-Ethernet LLC2 Conversion

After you change the translation behavior to perform Token Ring LLC2 frames into Ethernet 0x80d5 format frames, some of the non-IBM hosts in your network topology might use the standard Token Ring conversion of Token Ring LLC2 to 802.3 LLC2 frames. If this is the case, you can change the translation method of those hosts to use the standard translation method on a per-DSAP basis. The translation method for all the IBM hosts would still remain as Token Ring LLC2 to Ethernet 0x80d5 translation.

To define non-IBM hosts in your network topology to use the standard translation method while the IBM hosts use the nonstandard method, use the following command in global configuration mode:

Command	Purpose
source-bridge sap-80d5 dsap	Allow some other devices to use normal LLC2/IEEE 802.3 translation on
	a per-DSAP basis.

BC-122Bridging and IBM Networking Configuration Guide