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To bind to an 802.2 address, the client sends a DL_BIND_REQ with the dl_sap field set to the SSAP. This is an even value in the range 0 to 254 (0x0 to 0xFE). The dl_xidtst_flg field may optionally have either or both of the DL_AUTO_XID or DL_AUTO_TEST bits set.
If the SSAP is 0xAA, then the client should follow the acknowledgment of the bind with a DL_SUBS_BIND_REQ with a 5-byte SNAP. The dl_subs_bind_class field should be set to DL_HIERARCHICAL_BIND. The message for enabling a SNAP is shown in Figure 14-2.
Figure 14-2 Message for enabling a SNAP
Attempting to perform a hierarchical subs_bind operation to any service access point (SAP) value other than 0xAA will cause an error.
After successfully binding to an 802.2 SAP, the client may enable a group SAP by sending a DL_SUBS_BIND_REQ with a 2-byte DLSAP containing the group SAP. Valid group SAPs are odd numbers in the range 1 to 253 (0x1 to 0xFD). In this case, the dl_subs_bind_class field should be set to DL_PEER_BIND. Note that SAP 255 (0xFF) is the global (broadcast) SAP and is always enabled. The message for enabling a group SAP is shown in Figure 14-3.
Figure 14-3 Message for enabling a group SAP
For a description of group and global SAPs, see ANSI/IEEE Standard 802.2-1985.
As a special case, a client may request that it receive all 802.2 packets that come in. It does so by sending a DL_SUBS_BIND_REQ with a 2-byte DLSAP set to 0. The dl_subs_bind_class field should be set to DL_PEER_BIND.
When sending packets to DLSAP 0xFF, it is ambiguous whether the packet is destined for an 802.2 global SAP or an IPX SAP. The ambiguity is resolved by declaring that only an IPX endpoint can send to another IPX endpoint and an IPX endpoint cannot send to a global SAP.