user manual

Configuring Data-Link Switching Plus
Technology Overview
BC-283
Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02
UDP Unicast
DLSw Version 2 uses UDP unicast in response to an IP multicast. When address resolution packets
(CANUREACH_EX, NETBIOS_NQ_ex, NETBIOS_ANQ, and DATAFRAME) are sent to multiple
destinations (IP multicast service), DLSw Version 2 sends the response frames (ICANREACH_ex and
NAME_RECOGNIZED_ex) via UDP unicast.
UDP unicast uses UDP source port 0. However, some firewall products treat packets that use UDP source
port 0 as security violations, discarding the packets and preventing DLSw connections. To avoid this
situation, use one of the following procedures:
• Configure the firewall to allow UDP packets to use UDP source port 0.
• Use the dlsw udp-disable command to disable UDP unicast and send address resolution packets in
the existing TCP session.
Enhanced Peer-on-Demand Routing Feature
DLSw Version 2 establishes TCP connections only when necessary and the TCP connections are brought
down when there are no circuits to a DLSw peer for a specified amount of time. This method, known as
peer-on-demand routing, was recently introduced in DLSw Version 2, but has been implemented in Cisco
DLSw+ border peer technology since Cisco IOS Release 10.3.
Expedited TCP Connection
DLSw Version 2 efficiently establishes TCP connections. Previously, DLSw created two unidirectional
TCP connections and then disconnected one after the capabilities exchange took place. With DLSw
Version 2, a single bidirectional TCP connection establishes if the peer is brought up as a result of an IP
multicast/UDP unicast information exchange.
DLSw+ Features
DLSw+ is Cisco’s version of DLSw and it supports several additional features and enhancements.
DLSw+ is a means of transporting SNA and NetBIOS traffic over a campus or WAN. The end systems
can attach to the network over Token Ring, Ethernet, Synchronous Data Link Control (SDLC) Protocol,
Qualified Logical Link Control (QLLC), or Fiber Distributed Data Interface (FDDI). See the DLSw+
Design and Implementation Guide Appendix B, “DLSw+ Support Matrix,” for details. DLSw+ switches
between diverse media and locally terminates the data links, keeping acknowledgments, keepalives, and
polling off the WAN. Local termination of data links also eliminates data-link control timeouts that can
occur during transient network congestion or when rerouting around failed links. Finally, DLSw+
provides a mechanism for dynamically searching a network for SNA or NetBIOS resources and includes
caching algorithms that minimize broadcast traffic.
DLSw+ is fully compatible with any vendor’s RFC 1795 implementation and the following features are
available when both peers are using DLSw+:
• Peer groups and border peers
• Backup peers
• Promiscuous and on-demand peers
• Explorer firewalls and location learning
• NetBIOS dial-on-demand routing feature support