![[previous]](../../../graphics/l_arrow.gif){kind=icon}
![[next]](../../../graphics/r_arrow.gif){kind=icon}
This chapter describes how to configure your system to perform multicast data link switching (DLSw). Multicast DLSw allows easier scalability of large DLSw networks while reducing the number of configuration steps required. Multicast DLSw provides an enhancement to the RFC 1795-compliant DLSw described in the Configuring Data Link Switching for SNA and NetBIOS Networks chapter. Multicast DLSw provides the following enhancements:
With RFC 1795-compliant DLSw, each data link switch in partially meshed or fully meshed networks must be configured for one or more peers so that TCP connections can be established between the DLSw peers. With multicast DLSw, IP multicast addresses are used for exploration, which eliminates the requirement that DLSw peers must be configured.
With RFC 1795-compliant DLSw, each data link switch sends out broadcast CANUREACH_ex Switch-to-Switch Protocol (SSP) requests on every TCP connection. With multicast DLSw, only one multicast packet is sent out by a data link switch, which reduces WAN backbone traffic.
With RFC 1795-compliant DLSw, each data link switch has two TCP connections with each of its peers, whether or not a circuit is established between end systems through the DLSw peers. With multicast DLSw, TCP connections are brought up only if a circuit needs to be established between the data link switches. The TCP connections are brought down when all circuits using the connection have ended.
Before you configure multicast DLSw, MOSPF must be configured. For information, see the Configuring IP Multicast Routing chapter and the MOSPF Service Parameters chapter in Reference for Enterprise OS Software.
This section describes how to configure multicast DLSw for NetBIOS or SNA traffic. Multicast DLSw is useful in the following network topologies:
For configuration procedures for NetBIOS, see the next section. For configuration procedures for SNA client and server environments, see "Configuring Multicast DLSw for SNA Client and Server Environments" later in this chapter.
DVMRP is not supported with DLSw multicast.
This section describes how to configure multicast DLSw for NetBIOS meshed environments. In this configuration, DLSw bridge/routers can use the default multicast address for both transmit and receive traffic.
Before beginning this procedure, complete the following tasks:
Figure 251 is an example of a meshed NetBIOS environment. In the figure, four DLSw bridge/routers are participating in the multicast environment.
Figure 251 
DLSw Multicast Example (Meshed NetBIOS Environment)
To configure multicast DLSw as shown in the figure, follow these steps on each bridge/router:
1 . Set the DLSw mode on the bridge/router to multicast by entering:
SETDefault -DLSw MOde = Multicast
When configuring the bridge/router for multicast mode, you can also include the RouteInfo/NoRouteInfo parameter in the SETDefault command. This parameter applies only when DLSw is configured to operate under multicast mode and specifies whether DLSw loop detection passes along route information when sending a loop frame to a multicast address. The default is NoRouteInfo. For more information, see "Enabling DLSw Loop Detection" in the Configuring Data Link Switching for SNA and NetBIOS Networks chapter.
2 . Enable NetBIOS for DLSw by entering:
SETDefault -DLSw CONTrol = EnableNetBios
3 . Enable IP routing by entering:
SETDefault -IP CONTrol = Route
4 . Enable multicast IP routing by entering:
SETDefault -MIP CONTrol = Enable
5 . Enable OSPF on the DLSw port using:
SETDefault !<port> -OSPF CONTrol = Enable
6 . Enable multicast OSPF on the DLSw WAN port using:
SETDefault !<port> -MOSPF CONTrol = Enable
This section describes how to configure multicast DLSw for SNA client and server environments. In these configurations, one data link switch router is connected to an SNA host and a second data link switch router is connected to clients (PU2). You need to configure the appropriate multicast DLSw addresses on the client and the server routers.
Because you need to configure the multicast DLSw address on both sides, the benefit of using DLSw multicast for SNA client and server environments is limited. The primary benefit of using DLSw multicast instead of RFC 1795-compliant DLSw is that the TCP connections come up dynamically as needed and go down when the circuit becomes idle.
Before beginning this procedure, complete these tasks:
To configure multicast DLSw on the SNA client, follow these steps:
1 . Set the DLSw mode on the bridge/router to multicast by entering:
SETDefault -DLSw MOde = Multicast
2 . Delete the default multicast address by entering:
DELete -DLSw MulticastAddr DEFault
3 . Define the Class D multicast address that the client bridge/router will receive SNA traffic on using:
ADD -DLSw MulticastAddr <IP multicast address> SNA Rx
ADD -DLSw MulticastAddr 224.0.10.100 SNA Rx
4 . Define the Class D multicast address that the client bridge/router will transmit SNA traffic on using:
ADD -DLSw MulticastAddr <IP multicast address> SNA Tx
ADD -DLSw MulticastAddr 224.0.10.200 SNA Tx
5 . Enable IP routing by entering:
SETDefault -IP CONTrol = Route
6 . Enable multicast IP routing by entering:
SETDefault -MIP CONTrol = Enable
7 . Enable OSPF on the port using:
SETDefault !<port> -OSPF CONTrol = Enable
8 . Enable multicast OSPF on the port using:
SETDefault !<port> -MOSPF CONTrol = Enable
ADD -DLSw MulticastAddr 224.0.10.200 SNA Rx
ADD -DLSw MulticastAddr 224.0.10.100 SNA Tx
Figure 252 is an example of an SNA configuration in which multicast DLSw is used. Table 72 lists the commands to configure on each DLSw client and server bridge/router to allow multicast DLSw to work.
Figure 252 
DLSw Multicast Example (SNA Configuration)
This section describes how to customize the multicast DLSw configuration.
You can tune the retry interval and retry count for the number of times that the SSP frames sent on multicast are retried. The default retry interval is 3 seconds for SNA and 1 second for NetBIOS, and the default retry count is 0 (no retries). To change the retry interval and retry count, use:
SETDefault -DLSw McastRetry = <SNA | NetBios> <retry interval (1-5)> <retry count (0-5)>
You must also specify whether the change is for SNA or NetBIOS traffic.
You can also specify the number of minutes that a TCP connection between multicast DLSw peers will stay up without any circuit using the connection. To change the TCP idle time, use:
SETDefault -DLSw McastTcpIdle = <timer duration (1-255)>
The default is 3 minutes.
If you want to restore the default multicast address (224.0.10.0) on the bridge/router after previously configuring an address for multicasting purposes, enter:
ADD -DLSw MulticastAddr DEFault
When you specify DEFault, the traffic type defaults to ALL and the usage defaults to TxRx.
To disable DLSw multicast on the bridge/router, enter:
SETDefault -DLSw MOde = NoMulticast
The bridge/router stops sending out multicasts to DLSw stations on the network.