Abstract

Routers and SNA: Improving the State of the Art

This October 1994 Data Communications lab test, conducted by Kevin Tolly of The Tolly Group and David Newman of Data Communications, evaluated routers designed to carry IBM SNA and NetBIOS traffic across routed enterprise WANs. The article focused on whether emerging router-based approaches, including Data Link Switching (DLSw) and vendor-specific alternatives, could make SNA and NetBIOS routing practical while preserving session stability and allowing network managers to prioritize mission-critical traffic.

The lab tested five SNA-aware routers from Cisco Systems, Crosscomm, Proteon, 3Com, and Wellfleet Communications. IBM was invited but did not participate. The products were evaluated for SNA routing, NetBIOS routing, IP/IPX/AppleTalk and other multiprotocol support, WAN-port capacity, routing throughput, prioritization behavior, and the ability to keep SNA sessions stable under congestion. The test environment used IBM PS/2 Model 76 PCs running CommManager/2 and LANStreamer Token Ring adapters, a NetWare server, an FTP server, Network General Expert Sniffer, Wandel & Goltermann analyzers, and simulated WAN links including T1 and 56Kbit/s conditions.

The results showed that SNA and NetBIOS routing had improved significantly. All five tested vendors demonstrated approaches for moving SNA traffic across routed backbones, and the lab found that DLSw and related technologies could prevent some of the session instability that historically made SNA routing difficult. The arrival of DLSw was an important development because it terminated LLC2 sessions locally and encapsulated SNA traffic across the WAN, reducing the impact of WAN congestion on end stations.

Cisco Systems’ Cisco 4500 received a Data Communications “Tester’s Choice” designation. The article cited the Cisco 4500’s strong all-around performance, support for SNA and NetBIOS routing, and especially its ability to handle routing and prioritization challenges more successfully than the other products tested. Proteon’s CNX 600 performed strongly in pure SNA throughput tests and, in some cases, ran slightly faster than the Cisco 4500. Wellfleet’s Backbone Link Node, 3Com’s NetBuilder II, and Crosscomm’s ILAN products also demonstrated useful SNA-aware routing capabilities, but the lab found more uneven behavior when prioritization, congestion, and mixed protocol traffic were introduced.

Prioritization was the most difficult area. The lab attempted to divide WAN bandwidth among SNA, NetBIOS, IP, and IPX traffic and then verified whether each router could maintain those allocations under load. Some products could protect SNA reasonably well, but the article warned that prioritizing both SNA and NetBIOS remained risky. In several cases, routers were unable to allocate bandwidth precisely, and in a few scenarios SNA sessions crashed outright. The lab concluded that prioritization worked best when policies were simple and when routers could clearly distinguish traffic classes.

Overall, the article concluded that router vendors had made major progress in supporting SNA and NetBIOS over routed WANs. DLSw and related mechanisms made the technology far more practical than earlier source-route bridging approaches, but the market was not yet fully mature. For enterprise buyers, the key lesson was that SNA-aware routing could reduce dependence on parallel networks and improve multiprotocol WAN integration, but products still needed careful testing for session stability, prioritization accuracy, and behavior under congestion.

Solutions Tested

Cisco Systems — Cisco 4500
Crosscomm — ILAN XL80 and ILAN XL20
Proteon — CNX 600
3Com — NetBuilder II
Wellfleet Communications — Backbone Link Node