[Top] [Prev] [Next] [Bottom]

Using the DLSw Protocol

This chapter describes the Nx Networks implementation of the Data Link Switching (DLSw) protocol. The DLSw protocol offers a wide range of functionality that enables you to integrate LAN-based SNA traffic into heterogeneous Wide Area Networks (WANs). This implementation of the DLSw protocol includes support of RFC 1795 (DLSw V1.0), handling both NetBIOS and SNA traffic.

The following sections explain how to configure your router for DLSw:

About DLSw

Setting Up DLSw

Sample DLSw Configuration 1

Sample DLSw Configuration 2

On Demand and Explicitly Configured TCP Sessions

Using DLSw Groups

Mixing PU2.0 and T2.1 Link Stations on Multipoint Lines

About DLSw

DLSw is essentially a forwarding mechanism for NetBIOS and SNA protocols over both SDLC and LLC2 data links. It relies on the Switch-to-Switch protocol (SSP) running over TCP/IP to provide a reliable transport of SNA traffic over the internet. DLSw does not provide full routing capabilities. Instead, it works by providing switching at the data link layer. Rather than bridging LLC2 frames, DLSw terminates the LLC2 connection locally and encapsulates only the Information (I) and Unnumbered Information (UI) frames in TCP frames. The router ships the TCP frames over the WAN link to a neighbor DLSw router for delivery to their intended end station addresses.

How DLSw Works

LLC2 and SDLC are connection-oriented protocols. DLSw gives these protocols the dynamic characteristics of routable protocols. Equally important, DLSw preserves the end-to-end reliability and control features that make LLC2 and SDLC effective for communication.

Problems Inherent in the Bridging Solution

Figure 1 illustrates the traditional approach to bridging LLC2 frames across WAN links. The problem with this approach is that network delays occur much more frequently in the WAN than on a LAN. Such delays can arise from simple network congestion, slower line speeds, or other factors. Each of these factors increases the possibility of a session timing out and of data failing to arrive at the destination.

In addition, LAN protocols like LLC2 use much shorter retransmit/response times than those designed for use in the WAN. This makes maintaining end-to-end connections across WAN links extremely difficult, causing session timeouts to occur.

The frequency of session timeouts is not the only problem. Another problem arises when data is delayed while crossing the WAN. When a sending station retransmits data that is not lost, but delayed, LLC2 end stations may end up receiving duplicate data. While this would seem to safeguard the data, it can lead to confusion of the LLC2 procedures on the receiving side. This may, in turn, lead to inefficient use of the WAN link.

Figure 1 Traditional Approach to Bridging Across WAN Links

Protocol Spoofing

To reduce the chance of session timeouts and to maintain the appearance of end-to-end connectivity for sending stations, DLSw works by terminating or spoofing LLC2 connections at the local router. When terminating the connection, the local router sends acknowledgments to the sending station. The acknowledgment tells the sender that data previously transmitted have been received, and prevents the station from retransmitting.

From this point forward, assuring that data gets through is the responsibility of the DLSw software. The software accomplishes this by encapsulating the data in routable IP frames, then transporting them (via TCP) to a DLSw peer. The neighbor DLSw router strips away the frame headers, determines the address of the data's intended recipient, and establishes a new LLC2 connection with that end station. Figure 2 illustrates this relationship between two DLSw neighbor routers.

Figure 2 Data Link Switching Over the Wide Area Network

SDLC Data Link Support

In addition to LAN data link support for SNA (LLC2) and NetBIOS, DLSw supports SDLC data link termination for SDLC-attached SNA devices. You can configure the router to act in either a primary or a secondary local link role. Support for SNA data link type is independent of the corresponding neighbor DLSw router; that is, the local router can have SDLC devices attached and the remote router's SNA devices can be on a Token Ring (LLC2).

Figure 3 SDLC Support

Primary and Secondary Link Roles

In Figure 3, if the DLSw router is in the primary link role, the router polls downstream SNA PU2.0 or T2.1 devices such as IBM 3174 cluster controllers or the AS/400, respectively. If the router is in the secondary link role, the adjacent (primary) station polls the router. An example of a local secondary link configuration is where the SDLC link connects the router to a Front End Processor (FEP), such as 3745. Another example is where the router is SDLC-attached to a T2.1/APPN device, such as an AS/400, and the T2.1 device acts as a primary link station.

You can configure the type of SNA node (PU2 or T2.1) for each SDLC link station. In addition to the link role consideration, the router uses the node type to determine whether or not to forward XID frames to the adjacent physical device.

For example, a local station configured with a PU2 node type on a local primary link does not forward NXID frames it receives to the actual attached device. Instead, the router generates the appropriate XID0 response using the configured IDNUM and IDBLK values directly. This feature isolates the actual physical device configuration from the IBM host's configuration parameters, and permits, for example, transparent substitution of a remote SDLC device for an existing local Token Ring configuration.

With T2.1 SDLC devices, on the other hand, the router explicitly forwards all XID frames end-to-end, allowing XID3 parameter negotiation support. Mixed node types may be supported on a single multidrop physical link.

Both SDLC link role configurations support multiple adjacent link stations (devices) on one physical link. In the case of SDLC secondary, you can configure the router for multiple stations, as one of several stations on the physical line, or both.

Negotiable Link Role

In addition, you can configure SDLC link role as negotiable. In Figure 3, the router allows SDLC XID frames to flow in both directions until the router determines the role of its adjacent link station, after which the local role dynamically resolves to the appropriate value. This feature is intended to primarily support end-to-end T2.1/APPN traffic, where the respective end station resolves its role dynamically, using XID3 frames. The router does not support dynamic role negotiation on multipoint links or dynamic T2.1 link station address resolution.

If you configure respective SNA T2.1 end stations for role negotiation, but configure the router with a non-negotiable link role (the role is primary or secondary), the router attempts to "bias" the role negotiation protocol such that the local link station role is resolved accordingly.

Group Poll Feature

In addition to the SDLC link role flexibility that DLSw offers, the router also supports the Group Poll (IBM GP3174) feature when you configure the router for local secondary multipoint, since the adjacent primary link station, typically an IBM mainframe, need only issue a single unnumbered poll to simultaneously address all stations suitably configured on the router.

Benefits of DLSw

Because DLSw terminates the LLC connection at the local router, it is especially effective at eliminating SNA session timeouts and reducing WAN overhead on shared circuits. The protocol has these main benefits:

Reduces the possibility of session timeouts by terminating LLC2, NetBIOS, and SDLC traffic at the local LAN.
Reduces WAN network overhead by eliminating the need to transmit Receive Ready (RR) acknowledgments over the WAN. DLSw confines the RRs to the LANs that are local to each DLSw router.
Provides flow and congestion control and broadcast control of search packets between DLSw routers and their attached end stations.
Increases Source Route Bridging (SRB) hop-count limits.
Allows protocol conversion from LLC2 to SDLC.
Supports NetBIOS traffic.

Setting Up DLSw

The following sections explain the procedures to follow to set up DLSw:

Configuration Requirements
Configuring Adaptive Source Route Bridging (ASRT) for DLSw, as needed.
Configuring IP for DLSw
Configuring SDLC Interfaces
Configuring DLSw

In addition, a sample DLSw configuration with explanatory notes begins on page 19.

Configuration Requirements

OpenROUTE software supports DLSw over IEEE 802.5 Token Ring, SDLC, Ethernet, and FDDI. To use DLSw, you must perform the following actions:

Configure ASRT, as needed
Configure IP
Configure OSPF and MOSPF, as needed
Configure SDLC devices, as needed
Configure DLSw

The sections that follow explain step-by-step how to complete these actions. Examples of actual DLSw configurations follow these procedures.

Configuring Adaptive Source Route Bridging (ASRT) for DLSw

Since the DLSw router appears as a bridge to attached end stations, you need to configure source route bridging. Note that in SDLC-only configurations, you do not need to set up ASRT.

Follow these steps to configure:

1. Enter protocol bridge at the Config> prompt to enter the bridging configuration module.

2. Enter enable bridge to enable bridging on the router. Each bridge must have a unique bridge address.

3. Enter add port to add a bridge port for each interface that DLSw will use. The display prompts you for an interface number and a port number.

4. Configure LAN interfaces.

For Token Ring interfaces:

Enter disable transparent to disable transparent bridging. Then, enter enable source routing to turn on source routing for the bridge port. You will be prompted for an SRB segment number.
For Ethernet or FDDI interfaces:

Enter enable transparent to enable transparent bridging on the bridge port.

5. If you are configuring the router for parallel DLSw and bridging paths, create a protocol filter against the SAPs (Service Access Points) you intend DLSw to use. If the router is performing bridging operations, plus forwarding packets via DLSw, it is essential to do this. If you do not, DLSw will both bridge and forward the packets it receives.

To create a SAP filter,

Enter add protocol-filter dsap 4 at the Bridge config> prompt.
Specify the bridge port to which the filter applies. The command tells the router to filter all traffic that has a DSAP of 4 on a designated port. (Note that this assumes you have chosen a SAP of 4 for DLSw traffic. Assigning a SAP is something you do during the DLSw configuration.)

6. Next, verify the ASRT configuration using the list bridge command. You do not have to do this, but it is a good idea to check the bridge configuration before proceeding.

7. Enable the DLSw protocol using the enable dls command.

Configuring IP for DLSw

You need to configure IP so the local DLSw router can form the TCP connection to its DLSw peer. To do this, proceed as follows:

1. At the Config> prompt enter protocol ip to display the IP configuration prompt.

2. Enter add address to assign the IP address to the hardware interface you are using to connect to the other DLSw peer.

3. Enable dynamic routing:

If you do not define static routes between DLSw neighbors, you must choose either OSPF or RIP as your routing protocol. Using OSPF is recommended, because it entails less network overhead than RIP.

To enable OSPF, enter protocol ospf at the Config> prompt. This brings you to the OSPF Config> prompt. To use DLSw group functionality, enable Multicast OSPF.

For more information on using OSPF, see OSPF in the Online Library.
To enable RIP, enter enable rip at the IP Config> prompt.

4. Enter set internal-ip-address to set the address for the router as a whole. The router uses the internal IP address when it connects via TCP with its DLSw peer.

Note: If you are using RIP, the router's internal IP address must match the IP address assigned to a hardware interface.

Configuring SDLC Interfaces

You must configure SDLC links if you intend to support SDLC over DLSw. This section explains how to access the SDLC configuration process and describes SDLC-related commands.

For more information on these commands, see Configuring and Monitoring SDLC Interfaces.

1. At the Config> prompt, enter set data-link sdlc to set the data-link protocol for the serial interface. The router prompts you for an interface number. To see a list of interface numbers, enter list devices at the Config> prompt.

2. At the Config> prompt, enter network to display the SDLC configuration prompt. The router prompts you for an interface number. Enter the following commands at this prompt.

3. Use the SDLC stations that you configure in DLSw or use the add station command to explicitly set up SDLC stations in the following situations:

The following defaults for SDLC stations are not satisfactory:

-Maximum BTU is maximum allowable by interface
-Tx and Rx Windows are 7 for MOD 8, 127 for MOD 128
The SNA devices on the link are of mixed node types.
You want to use the group poll feature.
You want greater flexibility and control by using the SDLC monitoring commands.

If you do not explicitly add SLDC stations, the router assumes the following:

The attached stations are of type PU2 if the router's link role is primary or secondary.
The attached stations are of type T2.1 if the router's link role is negotiable.

4. Change the link role to secondary or negotiable using the set link role command if primary, the default link role, is not satisfactory. Configuring the role values so that they are not conducive to each other and to the actual SNA devices in use can prevent successful link activation. Configure the link role as follows:

Specify secondary if the SDLC link is connected to an adjacent SDLC primary device, such as a FEP.
Specify negotiable if a T2.1 (APPN) device is attached and you anticipate XID3 exchange.

Connecting multiple T2.1 devices on a multidrop link by definition denotes that true link role negotiation is not being performed, and you should use a predefined link role on both the router and the T2.1 device(s).

It is not required that the respective T2.1 devices perform true end-to-end role negotiation when you configure the router's link as negotiable; the router senses the actual role, whether predetermined or not, and adjusts accordingly. Conversely, if you anticipate end-to-end T2.1 role negotiation and do not configure the router's link role as negotiable, the value you configure influences the role negotiation.

5. Set up group polling for secondary stations on the link if you wish. To set up a group poll, set a group poll address using the set link group-poll command and then use the add station and set station group-inclusion commands to include stations in the group poll list.

The router supports group polling only when the local link role negotiates to secondary. It also requires a corresponding configuration on the adjacent SDLC primary side of the link. This is typically an IBM mainframe running IBM's Network Control Program (NCP) software; if so, use the GP3174 keyword on the PU definition statement to designate group polling.

6. For RBX Series routers, set the cable type using the set cable command.

7. Enter list link to verify the SDLC configuration. To change any of the parameters, use the set commands described in Configuring and Monitoring SDLC Interfaces.

Configuring DLSw

Before you begin configuring DLSw, enter list device at the Config> prompt to list the interface numbers of different devices.

To configure the DLSw protocol, follow these steps.

1. At the Config> prompt, enter protocol dls. This brings you to the DLSw config> prompt.

2. Enter enable dls to enable DLSw in the router.

3. If your configuration is handling LLC2 or NetBIOS traffic, enter set srb to designate an SRB (Source Route Bridging) segment number for the DLS router.

This segment number should be the same for all DLSw routers, and unique in the SRB domain. The bridge uses this number in the Routing Information Field (RIF) when the router sends the frames on the LAN. The segment number is the key to preventing loops.

4. Enter open-sap for each SAP that you wish DLSw to switch. The router prompts for interface numbers. To open commonly used SNA SAPs (0, 4, 8, and C), specify SNA. To open the NetBIOS SAP, specify NB or F0. To open the LNM SAP, specify LNM or F4.

You do not need to open SAPs in a pure DLSw/SDLC router configuration.

Note: If you enable SAP List Filtering, you must open SAPs on the target DLSw router.

5. Use the add tcp command to add the IP address of each DLSw neighbor. You can also make this connection using multicast OSPF using the join-group command.

Note: A router can participate in a group only if its neighbor router is a platform based on OpenROUTE running DLSw. If you configure one DLSw router for a group, you must enable OSPF and MOSPF on all DLSw routers in the group.

6. For your DLSw configuration to support SDLC, you must add an SDLC link station using the add sdlc command.

Adding SDLC link stations requires knowledge of the device link station address, the optional NodeID field information (IDNUM and IDBLK), and the source and destination MAC addresses and SAPs for mapping to the corresponding remote SNA device.

The link station address is required, and must match the address of the actual physical device you are connecting.

See the add sdlc command for more information.

Sample DLSw Configuration 1

Following is a complete DLSw configuration based on the information shown in Figure 4. The DLSw router being configured (R1 in the diagram) supports one LLC and one SDLC connection to its DLSw neighbor (R2). The SDLC interface is configured with the router's link role as primary (local primary), and it is polling an SDLC PU2.0 device. The TCP connection between the two routers is over PPP.

Configuring R1 for DLSw requires all of the information shown. This information includes the following:

The internal IP addresses of R1 and R2.
The IP address of each port used to maintain the TCP connection between the routers.
The interface numbers assigned to the Token Ring and SDLC devices and used for the TCP connection.
The source route bridge segment number of the attached Token Ring.

Figure 4 Context Diagram for DLSw Configuration

A second DLSw configuration shown in Figure 5 follows this example. This configuration includes both primary and secondary SDLC stations.

Adding Physical Devices

If your router platform requires you to add devices, add one Token Ring and two serial devices. For example:

Config>add device token ring
Device Slot # (0-2) [0]? 
Adding device as interface 0 

Config>add device quad-serial
Device Slot # (0-2) [1]? 
Adding device as interface 1 

Config>add device quad-serial
Device Slot # (0-2) [2]? 
Adding device as interface 2

After adding devices, you can list the devices to verify that you have assigned them to the appropriate router interfaces.

Config>list device 
Token Ring: CSR 80000000, vector 68 
Ethernet1 (SCC Ethernet): CSR  81600, CSR2  80C00, vector 94
WAN1 (SCC Serial Line): CSR  81620, CSR2  80D00, vector 93

Note: The format of this information differs depending on the router platform.

Configuring the Token Ring Device

Next, configure Token Ring. The list command shown here is not required at this point or at any other time during configuration of the router.

Config>network 0
Token-Ring interface configuration TKR config>speed 16
TKR config>media stpTKR config>list
Token-Ring configuration: Packet size (INFO field): 2052 
Speed:                    16 Mb/sec 
Media:                    Shielded 

RIF Aging Timer:          120 
Source Routing:           Enabled 
MAC Address:              000000000000 
IPX interface configuration record missing TKR config>exit

Configuring the WAN Interface

Use interface 1 for the WAN (TCP/IP) link. (See Figure 4.) The router defaults to PPP as the data link for the WAN. You can change the data link to PPP, X.25, or Frame Relay.

Config>network 1
Circuit Configuration

Circuit Config <NET-1> sl
Serial Line ConfigurationSerial Config <WAN1> list
Line Discipline:               SyncMaximum network layer frame size: 2048
Speed:                            2048000
HDLC Data encoding:               NRZ
HDLC Idle State:                  Flag
Transmit delay counter:           0 units
Cable:                            V.35 DCE
Synchronous clocking:             Internal

If necessary, use the set hdlc commands to change any of these defaults.

Note: For RBX Series platforms, you must set the cable type using the set cable command.

SLC Config>exit

Configuring the SDLC Device

The next step is to configure SDLC on interface number 2.

Set the Data Link to SDLC

Set the data-link protocol for serial interface number 2 to SDLC.

Config>set data-link sdlc
Interface Number [0]? 2

Display the SDLC Configuration Prompt

To access the SDLC configuration, enter network and the number of the SDLC interface (in this case, 2).

Config>network 2
SDLC user configuration 
Creating a default configuration for this link 
SDLC 2 Config>

Add an SDLC Station (optional)

See Configuring SDLC Interfaces for information on when and how to add SDLC stations. To add an SDLC station, enter add station.

SDLC 2 Config>add station
Enter station address (in hex) [C2]?
Enter station name [SDLC_C2]?
Include station in group poll list ([Yes] or No):
Enter max packet size [2048]?
Enter receive window [7]?
Enter transmit window [7]?
Enter PU2 or T2.1 node type [PU2]?

Configure the SDLC Link

Enter list link to display the current configuration of the SDLC link.

SDLC 2 Config>list link
Link configuration for: LINK_2   (ENABLED)
Role:        PRIMARY          Type:        POINT-TO-POINT
Duplex:      FULL             Modulo:      8
Idle state:  FLAG             Encoding:    NRZ
Clocking:    EXTERNAL         Frame Size:  2048
Speed:       0                Group Poll:  00
Cable:        V.36 DTE

Timers:    XID/TEST response:  2.0 sec
           SNRM response:      2.0 sec
           Poll response:      0.5 sec
           Inter-poll delay:   0.2 sec
           RTS hold delay:     DISABLED
           Inter-frame delay:  DISABLED
           Inactivity timeout: 30.0 sec
  
Counters:  XID/TEST retry:  4
           SNRM retry:      6
           Poll retry:      10

If any SDLC link settings do not apply to the link role, the software ignores them.

You can change any of these settings using the SDLC configuration commands described in Configuring and Monitoring SDLC Interfaces.

For RBX Series routers, you must set the cable type. For example:

SDLC 2 config>set cable rs-232 dte

Configuring Protocols

This section describes how to configure IP, OSPF (or RIP), bridging, and the DLSw protocol.

Configure IP

This example shows the creation of a minimal IP configuration.

To configure IP, begin by entering protocol ip at the Config> prompt:

Config>protocol ip
Internet protocol user configuration

Assign an IP Address to the WAN Link

Add an IP address and assign it to interface 1, the WAN link configured earlier:

IP config>add address
Which net is this address for [0]? 1
New address [0.0.0.0]? 128.185.236.33
Address mask [255.255.0.0]? 255.255.255.0

Set the Internal IP Address

Set the internal IP address. This is the address that remote DLSw routers use to connect to the router you are configuring. If you select RIP as the routing protocol for IP, the internal IP address must match the IP address configured for an interface.

IP config>set internal-ip-address 128.185.236.49

Enter list to display the newly added information.

IP config>list all
Interface addresses 
IP addresses for each interface: 
intf 1  128.185.236.33  255.255.255.0 Network broadcast, fill 0
Internal IP address: 128.185.236.49 Routing Protocols

BOOTP forwarding: disabled 
Directed broadcasts: enabled 
ARP Subnet routing: disabled 
RFC925 routing: disabled 
OSPF: enabled 
Per-packet-multipath: disabled 
RIP: disabled 

IP config>exit

Configuring OSPF or RIP

This sample configuration uses OSPF rather than RIP. You can use either of these routing protocols. However, if you choose RIP, you cannot use DLSw group functionality.

The list all command displays the current OSPF configuration.

Config>protocol ospf
Open SPF-Based Routing Protocol configuration console
OSPF Config>list all
 
                  --Global configuration-- 
          OSPF Protocol:          Disabled 
          External comparison:    Type 2 
          AS boundary capability: Disabled 
          Multicast forwarding:   Disabled 
 
                 --Area configuration-- 
Area ID       AuType     Stub?   Default-cost Import-summaries?
0.0.0.0       0=None     No      N/A           N/A

Enable OSPF

The first step consists of enabling OSPF and estimating the number of external routes and OSPF routers.

OSPF Config>enable ospf
Estimated # external routes [0]? 100
Estimated # OSPF routers [0]? 25

Enable Multicast OSPF as Needed

Since this example implements DLSw Group Functionality, you must enable multicast OSPF, as shown:

OSPF Config>enable multicast
Inter-area multicasting enabled? [No]: N

Define the Interfaces That Use OSPF

Enter set interface for every physical IP interface that will use OSPF. This example assumes that the backbone is the OSPF area (0.0.0.0). At this point, only one IP interface has been defined.

OSPF Config>set interface 128.185.236.33
Attaches to area [0.0.0.0]? 
Retransmission Interval (in seconds) [5]? 
Transmission Delay (in seconds) [1]? 
Router Priority [1]? 

Hello Interval (in seconds) [10]? 
Dead Router Interval (in seconds) [40]? 
Type Of Service 0 cost [1]? 
Authentication Key []? 
Retype Auth. Key []? 
Forward multicast datagrams? [Yes]: 
Forward as data-link unicasts? [No]: 
IGMP polling interval (in seconds) [60]? 
IGMP timeout (in seconds) [180]? 
OSPF Config>

Check the OSPF Configuration

Following is the OSPF display after it has been configured. To see what has changed in the configuration, compare this display with the display of the default OSPF configuration shown in Configuring OSPF or RIP.

OSPF Config>list all
 
            --Global configuration-- 
     OSPF Protocol:          Enabled 
     # AS ext. routes:       100 
     Estimated # routers:    25 
     External comparison:    Type 2 
     AS boundary capability: Disabled 
     Multicast forwarding:   Enabled 
     Inter-area multicast:   Disabled 
                             --Area configuration-- 
Area ID      AuType       Stub? Default-cost Import-summaries?
0.0.0.0      0=None       No         N/A           N/A 
 
                        --Interface configuration-- 
IP address      Area     Cost  Rtrns  TrnsDly  Pri  Hello  Dead
128.185.236.33   0.0.0.0   1      5       1      1     10    40
 
                            Multicast parameters 
IP address    MCForward    DLUnicast    IGMPPoll    IGMPtimeout
128.185.236.33    On           Off          60           180 OSPF Config>exit

Configuring Bridging

DLSw requires SRB (Source Route Bridging) to run over a Token Ring interface. Conversely, transparent bridging is required for Ethernet or FDDI devices, but does not work if the attached device is Token Ring.

This example is based upon a Token Ring connection to the DLSw router. Begin by enabling the bridge as shown:

Config>protocol bridge
Adaptive Source Routing Transparent Bridge user configuration
Bridge config>enable bridge

Disable Transparent Bridging

The list port command shows that the port defaults to transparent bridging.

Bridge config>list port
Port Id (dec)    : 128: 1, (hex): 80-01 
Port State       : Enabled 
STP Participation: Enabled 
Port Supports    : Transparent Bridging Only 
Assoc Interface  : 0 
Path Cost        : 0 
+++++++++++++++++++++++++++++++++++++++++++

Begin by disabling transparent bridging on the Token Ring port. Port number one is port 1 on interface 0. In other words, port 1 is the logical bridge port for the physical interface set up for the Token Ring (see Figure 4).

Bridge config>dis transparent
Port Number [1]?
Bridge config>

Enable Source Route Bridging

Next, enable source route bridging for the Token Ring port as shown:

Bridge config>enable source
Port Number [1]?

Assign a Port Segment Number and Enable DLSw

Now, assign a segment number for the port. You only have to assign segment numbers when configuring a source route bridge device, such as Token Ring. In this example (see Figure 4) b0b is the hexadecimal number assigned to the Token Ring device.

Segment Number for the port in hex(1 - FFF) [1]? b0b
Bridge number in hex (1 - 9, A - F) [1]?

After assigning a segment number, enable DLSw for the bridge.

Bridge config>enable dls

Listing the bridge configuration confirms that you have configured bridging correctly.

Bridge config>list bridge         Source Routing Transparent Bridge Configuration
        ================================================

Bridge    Enabled             Bridge Behaviour: Unknown
                   +----------------------------+
-------------------| SOURCE ROUTING INFORMATION |------------------
                   +----------------------------+
Bridge Number:         01             Segments:             1
Max ARE Hop Cnt:       14             Max STE Hop cnt:     14
1:N SRB:               Not Active     Internal Segment: 0x000
LF-bit interpret:      Extended

                   +-------------------+
-------------------| SR-TB INFORMATION |-------------------------------
                   +-------------------+
SR-TB Conversion:	Disabled TB-Virtual Segment: 0x000  MTU of TB-Domain:  0

                   +------------------------------------+
-------------------| SPANNING TREE PROTOCOL INFORMATION |--------------
                   +------------------------------------+
Bridge Address:    Default        Bridge Priority:    32768/0x8000
STP Participation: IEEE802.1d

                   +-------------------------+
-------------------| TRANSLATION INFORMATION |-------------------------
                   +-------------------------+
FA<=>GA Conversion: Enabled        UB-Encapsulation:  Disabled
DLS for the bridge: Enabled

                   +------------------+
-------------------| PORT INFORMATION |--------------------------------
                   +------------------+
Number of ports added: 1
Port:   1      Interface:  0  Behaviour:    SRB Only   STP:  Enabled

Implementing Protocol Filtering

This is an important step that is often neglected when configuring DLSw.

Note: You only need to implement the filter described here if you configure parallel bridging and DLSw. Such is not the case in this example. The procedure for creating a SAP filter is provided for reference purposes only.

Since DLSw, rather than bridging, forwards traffic on SAPs (Service Access Points) 04, 08, 0C, add a special protocol filter to the bridging set up.

The filter prevents the bridge from forwarding, on other ports, packets that only DLSw should handle.

The command shown below creates a filter that works on all packets with a destination SAP of 4. The list command issued subsequently displays the filter characteristics.

Bridge config>add prot-filter dsap 4
Filter packets arriving on all ports?(Yes or [No]): yesBridge config>list prot-f dsap
Protocol Class: DSAP 
Protocol Type : 04 
Protocol State: FILTERED 
Port Map      : 1 
========================== 
No ETHER type Filter Records Associated 
No SNAP Filter Records Associated

Once the filtering you need is in place, exit the bridging configuration module.

Bridge config>exit

Configuring DLSw

The final step involves configuring the DLSw protocol. The list command below shows the defaults.

Config>protocol dls
DLSw protocol user configuration 
DLSw config>list dlsDLSw is                            ENABLED
LLC2 send Disconnect is            ENABLED
Automatic TCP connection           ALWAYS CONNECT

SRB Segment number                 000
MAC <-> IP mapping cache size      128
Max DLSw sessions                  1000
DLSw global memory allotment       141056
LLC per-session memory allotment   8192
SDLC per-session memory allotment  4096
NetBIOS UI-frame memory allotment  40960

Database age timer                 1200  seconds
Max wait timer for ICANREACH       20    seconds
Wait timer for LLC test response   15    seconds
Wait timer for SDLC test response  15    seconds
Join Group Interval                900   seconds
Neighbor priority wait timer       2.0   seconds

Enable DLSw and set the SRB segment number. The segment number is the virtual segment number that identifies DLSw in the RIF of all LLC frames.

DLSw config>enable dls
DLSw config>set srb 020

Configuring DLSw Groups and Static Sessions

You must define either a DLSw group or a static TCP session to connect to a neighbor DLSw router. This example defines both a group and a static (explicitly configured) TCP session.

Use the join command to join a DLSw group. You designate each group member as Client, Server or Peer. Client is the default.

Using the Join-Group Command

The join-group command executed for R1 (see Figure 4), designates this DLSw router as a Client in group 1. To join this group, R2 has to be added as a Server in group 1. All clients in a group locate and establish TCP connections for DLSw with servers within the same group.

DLSw config>join
Group ID (1-64 Decimal) [1]? 
Client/Server or neighbor Group member (C/S/P)- [C]?
Transmit Buffer Size (Decimal) [5120]?
Receive Buffer Size (Decimal)  [5120]? 
Maximum Segment Size (Decimal) [1024]?
Enable/Disable Keepalive (E/D)- [D]?
Neighbor Priority (H/M/L) [M]?
DLSw config>list group
Group Role				Xmit Bufsize  Rcv Bufsize  Max Segsize  Keepalive   Priority
1   CLIENT       5120        	 5120           1024														DISABLED       MEDIUM

Using the Add TCP Command

The add tcp command creates explicitly configured DLSw routes. The neighbor DLSw IP address added here is the internal IP address of the neighbor DLSw router (called R2 in Figure 4). You must also configure R2 with the neighbor IP address of R1.

DLSw config>add tcp
Enter the DLSw neighbor IP Address [0.0.0.0]? 128.185.122.234
Transmit Buffer Size (Decimal) [5120]?
Receive Buffer Size (Decimal)  [5120]? 
Maximum Segment Size (Decimal) [1024]?
Enable/Disable Keepalive? (E/D) - [D]?
Neighbor Priority (H/M/L) [M]? 
DLSw>list tcp
Neighbor  				  Xmit Bufsize  Rcv Bufsize  Max Segsize  Keepalive  Priority
--------  				   ------------  -----------  -----------  ---------  -------- 
128.184.122.234       5120             5120            1024         DISABLED      MEDIUM

Define Each SDLC Link Station

You must define each SDLC link station as shown.

DLSw config>add sdlc
Interface # [0]? 2
SDLC Address [C1]? 
Source MAC Address [000000000000]? 4000003174d1
Idblk in Hex (0-0xfff) [0]? 
Idnum in Hex (0-0xfffff) [0]? 
LLC Source SAP (0 for auto-assign) [0]? 
LLC Destination SAP [4]? 
Destination MAC Address [000000000000]? 400000000002DLSw config>list sdlc all
Net  Addr   Status    Idblk  Idnum   Source SAP/MAC    Dest SAP/MAC
 4    C1    Enabled    017   A0021   00 40000003174d1  04 40000000002

You must assign a unique source MAC address to each SDLC link station. For PU2 SDLC devices, the values configured for Idnum and Idblk must match those configured for this PU in the machine with which the SDLC device wants to establish a connection.

Open SAPs

Next, open SAPs on each bridging interface that performs DLSw switching.

SAP numbers 0, 4, 8, and C are commonly used SNA SAPs. To open all of these SAPs, use the SNA option with the open-saps command as shown. To open SAPs for NetBIOS, choose NB. To open SAPs for LNM, choose LNM. You can also enter SAPs individually by entering a hexadecimal number.

DLSw config>open-sap
Interface # [0]?
Enter SAP in hex (range 0-F4), 'SNA', 'NB' or 'LNM' [4]? sna
SAPs 0 4 8 C opened on interface 0

Following is the DLSw display after configuring.

DLSw config>list dlsDLSw is                            ENABLED
LLC2 send Disconnect is            ENABLED
Automatic TCP connection           ALWAYS CONNECT

SRB Segment number                 0030
MAC <-> IP mapping cache size      128
Max DLSw sessions                  3000
DLSw global memory allotment       60000
LLC per-session memory allotment   8192
SDLC per-session memory allotment  4096
NetBIOS UI-frame memory allotment  40960

Database age timer                 1200  seconds
Max wait timer for ICANREACH       20    seconds
Wait timer for LLC test response   15    seconds
Wait timer for SDLC test response  15    seconds
Join Group Interval                900   seconds
Neighbor priority wait timer       2.0   seconds

When you have finished configuring DLSw, exit the DLSw configuration environment and restart the router.

DLSw config>exit
Config>restart
Are you sure you want to restart the gateway? (Yes or [No]): yes

Sample DLSw Configuration 2

Figure 5 shows a sample DLSw configuration using both Token Ring-to-SDLC and SDLC-to-SDLC neighbor DLSw circuits. Router R1 is running LLC2 over the Token Ring, communicating with the IBM mainframe on the remote end via router R2. Router R1 is also configured for SDLC itself (local primary role), connecting the 3174 controllers shown. Router R2 is connected to the IBM mainframe via SDLC; the mainframe is primary and router R2 therefore has its link configured as secondary (local secondary link role).

Figure 5 Sample DLSw Configuration using Primary and Secondary SDLC Stations

Most of the steps for this configuration are the same as those in the previous section for Figure 4. This section describes only the differences in how to set up SDLC and DLSw for this configuration.

Notice that the Destination SAP (DSAP) on the SDLC local primary router (R1) is 0 (zero), which puts the station in passive mode and prevents the primary router from attempting to establish a session. The DSAP on the secondary router is not set to zero, allowing that router to initiate sessions.

Because the FEP must poll the secondary router before the router can engage in session establishment, if the primary router attempts to establish a session and the secondary router is not being polled by the FEP, the attempt fails. Therefore, configuring the primary and secondary stations so that only the secondary router establishes sessions can avoid delays in establishing sessions. See the add sdlc command for more information on configuring DSAPs.

Configuring Router R1

On Router R1, the primary SDLC router, you need to

1. Set the SDLC link to multipoint.

SDLC 2 Config>set link type multipoint

2. In the DLSw configuration, add an SDLC station for each of the 3174s. See the add sdlc command for more information.

DLSw config>add sdlc
Interface # [0]? 2
SDLC Address [C1]? 
Source MAC Address [000000000000]? 401AAB9200C1
Idblk in Hex (0-0xfff) [0]? 
Idnum in Hex (0-0xfffff) [0]? 
LLC Source SAP (0 for auto-assign) [0]? 04
LLC Destination SAP [4]? 0
Destination MAC Address [000000000000]? 0000C91202C1
DLSw config>add sdlc
Interface # [0]? 2
SDLC Address [C1]? 
Source MAC Address [000000000000]? 400000317582 
Idblk in Hex (0-0xfff) [0]? 
Idnum in Hex (0-0xfffff) [0]? 
LLC Source SAP (0 for auto-assign) [0]? 04
LLC Destination SAP [4]? 0 
Destination MAC Address [000000000000]? 400000000002

Configuring Router R2

On Router R2, the secondary SDLC router, you need to

1. Set the SDLC link role to secondary.

SDLC 1 Config>set link role secondary

2. In the DLSw configuration, add SDLC stations to interface 1 for each of the 3274s.

DLSw config>add sdlc
Interface # [0]? 1
SDLC Address [C1]? 
Source MAC Address [000000000000]? 0000C91202C1
Idblk in Hex (0-0xfff) [0]? 
Idnum in Hex (0-0xfffff) [0]? 
LLC Source SAP (0 for auto-assign) [0]? 04
LLC Destination SAP [4]? 
Destination MAC Address [000000000000]? 401AAB9200C1
DLSw config>add sdlc
Interface # [0]? 1
SDLC Address [C1]? 
Source MAC Address [000000000000]? 400000000002 
Idblk in Hex (0-0xfff) [0]? 
Idnum in Hex (0-0xfffff) [0]? 
LLC Source SAP (0 for auto-assign) [0]? 04
LLC Destination SAP [4]? 
Destination MAC Address [000000000000]? 400000317582

On Demand and Explicitly Configured TCP Sessions

DLSw can automatically re-establish TCP sessions both after a session breaks and at startup. The software accomplishes this through the use of two DLSw configuration or monitoring commands.

enable auto-tcp-reconnect
disable auto-tcp-reconnect

The enable auto-tcp-reconnect command allows preconfigured TCP sessions to establish themselves automatically upon start-up, and causes broken sessions to re-establish. This is the default behavior for the router.

Note: The enable auto-tcp-reconnect command only applies if you have explicitly added TCP neighbor addresses. TCP sessions created through group membership always reconnect.

If you disable the default using disable auto-tcp-reconnect, DLSw sessions are not established until they are needed, and broken TCP sessions do not re-establish themselves until they are needed again. TCP group connections re-establish themselves after the interval specified using set timers expires. This command is available within the DLSw configuration and monitoring modules.

Using DLSw Groups

You can use DLSw Group capability to designate groups of DLSw routers. Setting up groups can be extremely beneficial, as it reduces the need for long lists of static IP addresses and the cost associated with maintaining them. A DLSw router can be a member of up to 64 groups.

There are three types of groups: Client, Server, and Peer-to-Peer. Routers designated as Servers only form DLSw connections with Client routers; likewise, Client routers can only form connections with Servers. In Peer-to-Peer groups, all routers form connections with each other.

Setting Up DLSw Groups

You need to configure OSPF and MOSPF if you want to use the DLSw group feature. Configuring OSPF or RIP provides instructions on how to configure these protocols.

Assign OSPF Addresses to Hardware Interfaces

Begin by entering protocol ospf at the Config> prompt to enter the OSPF configuration module. Enter set interface to assign the OSPF address to the hardware interface you are using to connect to the other DLSw neighbor.

Issue the DLSw Join-Group Command

At the DLSw config> prompt, enter join-group. The router prompts you for a group number, transmit and receive buffer sizes, type of membership in the group, and the neighbor priority for the group.

DLSw config>join-groupGroup ID (1-64 Decimal) [1]? 4
Client/Server or neighbor Group member (C/S/P)- [C]?
Transmit Buffer Size (Decimal) [5120]?
Receive Buffer Size (Decimal)  [5120]? 
Maximum Segment Size (Decimal) [1024]?
Enable/Disable Keepalive (E/D)- [D]?
Neighbor Priority (H/M/L) [M]?
DLSw config>

Enable OSPF and Multicast OSPF

Enable the OSPF routing protocol and OSPF multicast routing at the OSPF config> prompt, as shown:

OSPF Config>enable ospf
Estimated # external routes [0]? 100
Estimated # OSPF routers [0]? 25
OSPF Config>enable multicast
Inter-area multicasting enabled? [No]: 
OSPF Config>

Mixing PU2.0 and T2.1 Link Stations on Multipoint Lines

OpenROUTE software suppors co-existence of SNA PU2.0 and T2.1 link stations on SDLC multipoint lines.

By default, the OpenROUTE software treats all SDLC link stations as if they are of the same type. That is, these stations all function as either T2.0 (secondary) or T2.1 (negotiable) nodes from the router's perspective.

To mix roles among the link stations on a single SDLC link, you must configure the router to support whichever remote nodes do not match the default. Link station defaults are as follows:

MaxBTU

The maximum allowed by the interface

Receive Window

7 for MOD 8, 127 for MOD 128

Transmit Window

7 for MOD 8, 127 for MOD 128

Role

Primary

MaxBTU	The maximum allowed by the interface
Receive Window	7 for MOD 8, 127 for MOD 128
Transmit Window	7 for MOD 8, 127 for MOD 128
Role	Primary

To assign mixed roles to remote link stations, enter set link role from the SDLC command process. The set link role enables you to configure a particular link station as primary, secondary, or negotiable. Use this command after adding the remote secondary with the add station command.

[Top] [Prev] [Next] [Bottom]