IBM BC-203 manual DLSw+, BC-206

Page 4

Overview of IBM Networking

DLSw+

Note As previously stated, local acknowledgment for LLC2 is meant only for extreme cases in which communication is not possible otherwise. Because the router must maintain a full LLC2 session, the number of simultaneous sessions it can support before performance degrades depends on the mix of other protocols and their loads.

The routers at each end of the LLC2 session execute the full LLC2 protocol, which can result in some overhead. The decision to turn on local acknowledgment for LLC2 should be based on the speed of the backbone network in relation to the Token Ring speed. For LAN segments separated by slow-speed serial links (for example, 56 kbps), the T1 timer problem could occur more frequently. In such cases, it might be wise to turn on local acknowledgment for LLC2. For LAN segments separated by a FDDI backbone, backbone delays will be minimal; in such cases, local acknowledgment for LLC2 should not be turned on. Speed mismatch between the LAN segments and the backbone network is one criterion to be used in the decision to use local acknowledgment for LLC2.

There are some situations (such as host B failing between the time host A sends data and the time host B receives it) in which host A would behave as if, at the LLC2 layer, data was received when it actually was not, because the device acknowledges that it received data from host A before it confirms that host B can actually receive the data. But because both NetBIOS and SNA have error recovery in situations where an end device goes down, these higher-level protocols will resend any missing or lost data. These transaction request/confirmation protocols exist above LLC2, so they are not affected by tight timers, as is LLC2. They also are transparent to local acknowledgment.

If you are using NetBIOS applications, note that there are two NetBIOS timers—one at the link level and one at the next higher level. Local acknowledgment for LLC2 is designed to solve session timeouts at the link level only. If you are experiencing NetBIOS session timeouts, you have two options:

Experiment with increasing your NetBIOS timers.

Avoid using NetBIOS applications on slow serial lines.

In a configuration scenario where RSRB is configured between Router A and Router B and both routers are not routing IP, a Host connected to router A through Token Ring (or other LAN media) has no IP connectivity to router B. This restriction exists because IP datagrams received from the Host by Router A are encapsulated and sent to router B where they can only be de-encapsulated and source-bridged to a Token Ring. In this scenario, IP routing is recommended. To enable the Host to reach Router B in this scenario, IP routing should be enabled on Router A’s Token Ring interface to which the Host is attached.

DLSw+

Data-Link Switching Plus (DLSw+) is a method of transporting SNA and NetBIOS. It complies with the DLSw standard documented in RFC 1795 as well as the DLSw Version 2 standard. DLSw+ is an alternative to RSRB that addresses several inherent problems that exist in RSRB, such as:

SRB hop-count limits (SRB’s limit is seven)

Broadcast traffic (including SRB explorer frames or NetBIOS name queries)

Unnecessary traffic (acknowledgments and keepalives)

Data-link control timeouts

Cisco IOS Bridging and IBM Networking Configuration Guide

BC-206

Image 4
Contents Overview of IBM Networking BC-203Rsrb BC-204Configuration Considerations BC-205DLSw+ BC-206DLSw Version 2 Standard DLSw StandardBC-207 DLSw+ Features Enhanced Peer-on-Demand Routing FeatureIP Multicast UDP UnicastLocal Acknowledgment BC-209BC-210 LLC2 Session Without Local AcknowledgmentBC-211 DLSw+ Support for Other SNA Features BC-212Stun Networks Stun and BstunBC-213 Stun Features BC-214BC-215 BC-216 StunBstun Features LLC2 and Sdlc ParametersBstun Networks BC-217Cisco’s Implementation of LLC2 BC-218Cisco’s Implementation of Sdlc IBM Network Media TranslationBC-219 Virtual Token Ring Concept Sdllc Media Translation FeaturesBC-220 Resolving Differences in LLC2 and Sdlc Frame Size Maintaining a Dynamic RIF CacheOther Considerations BC-221Qllc Conversion BC-222Cisco’s Implementation of Qllc Conversion BC-223Comparing Qllc Conversion to Sdllc BC-224Other Implementation Considerations BC-225RFC 1490 Routed Format for LLC2 BNN BC-226RFC 1490 Bridged Format for LLC2 BAN BC-227BC-228 NciaNcia Client/Server Model Ncia ServerBC-229 BC-230 Ncia Server Client/Server ModelAdvantages of the Client/Server Model Extended ScalabilityMigration Support BC-231BC-232 AlpsDspu and SNA Service Point BC-233BC-234 Router Acting as a Dspu ConcentratorBenefits of SNASw SNA Switching ServicesBC-235 Reduced Configuration Requirements Scalable Appn NetworksIP Infrastructure Support Network Design SimplicityBranch Extender HPR Capable SNA Routing ServicesBC-237 Enterprise Extender HPR/IP BC-238Usability Features Dynamic CP Name Generation SupportDynamic SNA BTU Size Dlur Connect-OutManagement Enhancements LAN and IP-Focused Connection Types Trap MIB Support for Advanced Network Management AwarenessToken Ring, Ethernet, and Fddi Virtual Token RingDLC Switching Support for Access to Sdlc and Qllc Cisco Transaction ConnectionVirtual Data-Link Control Native IP Data-Link Control HPR/IPCtrc and Cics BC-243Ctrc and DB2 BC-244Benefits of Ctrc Cmcc Adapter HardwareBC-245 Channel Port Adapter Channel Interface ProcessorBC-246 Differences between the CIP and CPA Escon Channel Port AdapterParallel Channel Port Adapter BC-247Cmcc Adapter Features for TCP/IP Environments Common Link Access to WorkstationSupported Environments TCP/IP OffloadCisco Multipath Channel+ IP Host BackupBC-249 Cisco SNA Cmcc Adapter Features for SNA EnvironmentsBC-250 TN3270 Server Cisco Multipath ChannelBC-251 Telnet Server Functions SNA FunctionsBC-252 BC-253 BC-254