IBM BC-201 manual STUN and BSTUN, STUN Networks, BSTUN Features, page, BC-211

Overview of IBM Networking

STUN and BSTUN

Figure 88 VDLC Interaction with Higher-Layer Protocols

SNASw

DLSw+

Data-link users

			CLSI
Token	VDLC	Ethernet	Data-link controls
Ring
			51909

The higher-layer protocols make no distinction between the VDLC and any other data-link control, but they do identify the VDLC as a destination. In the example shown in , SNASw has two ports: a physical port for Token Ring and a logical (virtual) port for the VDLC. In the case of the SNASw VDLC port, when you define the SNASw VDLC port, you can also specify the MAC address assigned to it. That means data going from DLSw+ to SNASw by way of the VDLC is directed to the VDLC MAC address. The type of higher-layer protocol you use determines how the VDLC MAC address is assigned.

STUN and BSTUN

The Cisco IOS software supports serial tunnel (STUN) and block serial tunnel (BSTUN). Our BSTUN implementation enhances Cisco 2500, 4000, 4500, 4700, 7200 series routers to support devices that use the Binary Synchronous Communication (Bisync) data-link protocol and asynchronous security protocols that include Adplex, ADT Security Systems, Inc., Diebold, and asynchronous generic traffic. BSTUN implementation is also supported on the 4T network interface module (NIM) on the Cisco 4000 and 4500 series routers. Our support of the bisync protocol enables enterprises to transport Bisync traffic and SNA multiprotocol traffic over the same network.

This section contains the following topics:

•STUN Networks, page 211

•STUN Features, page 212

•BSTUN Networks, page 215

•BSTUN Features, page 215

STUN Networks

STUN operates in two modes: passthrough and local acknowledgment. Figure 89 shows the difference between passthrough mode and local acknowledgment mode.

The upper half of Figure 89 shows STUN configured in passthrough mode. In passthrough mode, the routers act as a wire and the SDLC session remains between the end stations. In this mode, STUN provides a straight passthrough of all SDLC traffic, including control frames.

The lower half of Figure 89 shows STUN configured in local acknowledgment mode. In local acknowledgment mode, the routers terminate the SDLC sessions and send only data across the WAN. Control frames no longer travel the WAN backbone networks.

	Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02		BC-211