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SDLLC is a software feature that enables a device on a Token Ring to communicate with a device on a serial link by translating between LLC2 and SDLC at the link layer. SDLLC is proprietary to Cisco Systems. A major difference between SDLLC and the SDLC Serial Tunneling (STUN) feature, which is covered in the "Configuring STUN and SDLC Local Acknowledgment" chapter, is that when configured for SDLLC, the router acts as an SDLC station; in contrast, when configured for STUN, the router functions as a passthrough through which SDLC frames can be transferred between two SDLC devices.
For a complete description of the commands mentioned in this chapter, refer to the "SDLLC commands" chapter of the Router Products Command Reference publication. For historical background and a technical overview of SDLLC, see the Internetworking Technology Overview publication.
Figure 1-1 illustrates how SDLLC provides link-level support for SNA communication.
As Figure 1-1 shows, SNA uses SDLC and LLC2 as link layer protocols to provide a reliable connection. The translation function between these industry standard protocols takes place in the proprietary Cisco software.
The SDLLC software allows a 37x5 front-end processor (FEP) on a Token Ring to communicate with a 3x74 cluster controller connected to a serial line in three basic topologies as follows:
In all of these topologies, each IBM end node (the FEP and cluster controller) has no indication that its counterpart is connected to a different medium running a different protocol. The 37x5 FEP responds as if the 3x74 cluster controller were communicating over a Token Ring, whereas the 3x74 responds as though the 37x5 FEP were communicating over a serial line. That is, the SDLLC software provides translation between the two media to be transparent to the end nodes.
Central to Cisco's SDLLC implementation is the concept of a virtual Token Ring device residing on a virtual Token Ring. Because the Token Ring device expects the node with which it is communicating also to be on a Token Ring, each SDLLC device on a serial line must be assigned an SDLLC virtual token ring address (SDLLC VTRA). Like real Token Ring addresses, SDLLC VTRAs must be unique across the network.
In addition to the SDLLC VTRA, an SDLLC virtual ring number (SDLLC VRN) also must be assigned to each SDLLC device on a serial line. (The SDLLC VRN differs from the virtual ring group numbers that are used to configure RSRB and multiport bridging.)
As part of its VTAM configuration, the IBM node on the Token Ring has knowledge of the SDLLC VTRA of the serial device with which it communicates. The SDLC VTRA and the SDLLC VRN are a part of the SDLLC configuration for the router's serial interface. When the Token Ring host sends out explorer packets with the SDLLC VTRA as the destination address in the MAC headers, the router configured with that SDLLC VTRA intercepts the frame, fills in the SDLLC VRNA and the bridge number in the Routing Information Field (RIF), and then sends the response back to the Token Ring host. A route is then established between the Token Ring host and the router. After the router performs the appropriate frame conversion, it uses this route to forward frames to this serial device.
IBM nodes on Token Ring media normally use frame sizes greater than 1 KB, whereas the IBM nodes on serial lines normally limit frame sizes to 265 or 521 bytes. To reduce traffic on backbone networks and provide better performance, Token Ring nodes should send frames as large as possible. As part of the SDLLC configuration on the router's serial interface, the largest frame size the two media will support should be selected. The router can fragment the frames it receives from the Token Ring device before forwarding them to the SDLC device; however, it does not assemble the frames it receives from the serial device before forwarding them to the Token Ring device.
SDLCC maintains a dynamic Routing Information Field (RIF) cache. SDLLC caches the entire RIF, that is, the RIF from the source station to destination station. The cached entry is based on the best path at the time the session began. SDLLC uses the RIF cache to maintain the LLC2 session between the router and the host FEP. SDLLC does not age these RIF entries. Instead, SDLLC places an entry in the RIF cache for a session when the session begins and flushes the cache when the session terminates. You cannot flush these RIFs, because if you flushed the RIF entries randomly, the router would not be able to maintain the LLC2 session to the host FEP.
You can perform the following tasks to configure SDLLC:
Configuration examples appear at the end of this section. For more information about any of the commands mentioned in the following sections, unless otherwise indicated, refer to the "SDLLC Commands" chapter of the Router Products Command Reference.
The 37x5 and 3x74 are connected to the same router. In this configuration, the LLC2 session extends from the 37x5 FEP across the Token Ring to the router. The SDLLC session extends from the router across the serial line to the 3x74 cluster controller. The SNA session extends across the Token Ring and the serial line to provide an end-to-end connection. The router is configured with source-route bridging (SRB).
To configure SDLLC with direct connection you must perform the following tasks:
For an example of how to configure SDLLC with direct connection, see the "Example of SDLLC with Direct Connection" later in this chapter.
The interfaces you will configure for SDLLC media translation are the serial interfaces that connect to the serial lines linking the remote SDLC devices. To configure them, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Enable SDLLC media translation on a serial interface. | sdllc traddr xxxx.xxxx.xx00 lr bn tr |
The XID value you define on the router must match that of the IDBLK and IDNUM system generation parameters defined in VTAM of the Token Ring host to which the SDLC device will be communicating. To define XID on the router, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Specify the XID value appropriate for the SDLC station to match VTAM values. | sdllc xid address xxxxxxxx |
The Token Ring host is always kept in a state ready to accept a connection from the remote serial device. The remote serial device is responsible for initiating connections. The advantage of this scheme is that the serial device can communicate with the Token Ring host whenever it chooses without requiring personnel to be on the host site.
The router actually initiates the connection on behalf of the serial device. To initiate connections, both the MAC address of the Token Ring host and the SDLC line address are required. You must configure the router to define the Token Ring host as the partner of the serial device. To do so perform the following task:
| Task | Command |
|---|---|
| Enable connections for SDLLC. | sdllc partner mac-address sdlc-address |
A router need not directly connect the two IBM end nodes, A 37x5 FEP on a Token Ring and a 3x74 cluster controller connected to a serial line can be connected to different routers. However, the router to which the 3x74 is connected must be configured with SDLLC. The routers communicate via RSRB using direct encapsulation, RSRB over an FST connection, or RSRB over a TCP connection. RSRB transports packets between Router A and Router B, while Router B performs all conversion between the LLC2 and SDLC protocols by means of the SDLLC software.
To configure the router for SDLLC with RSRB you must perform all the tasks in the "SDLLC with Direct Connection" section earlier in this chapter. In addition, you must perform one of the following sets of tasks. For more information about configuring RSRB, see the "Configuring Source- Route Bridging" chapter in this manual and the "Source-Route Bridging Commands" chapter in the Router Products Command Reference publication.
For an example of how to configure SDLLC with RSRB, see "Example of SDLLC with RSRB (Multiple 3x74s)" later in this chapter.
To configure SDLLC with RSRB using direct encapsulation, perform the following tasks in global configuration mode:
| Task | Command |
|---|---|
| Define a ring group. | source-bridge ring-group ring-group |
| Define a remote peer. | source-bridge remote-peername ring-group interface interface-name [mac-address] |
To configure SDLLC with RSRB over an FST connection, perform the following tasks in global configuration mode:
To configure SDLLC with RSRB over a TCP connection, perform the following tasks in global configuration mode:
| Task | Command |
|---|---|
| Define a ring group. | source-bridge ring-group ring-group |
| Define a remote peer. | source-bridge remote-peername ring-group tcp ip-address |
RSRB can be configured for only Local Acknowledgment with RSRB using IP encapsulation over a TCP connection. Configuring SDLLC Local Acknowledgment can reduce timeouts and keepalive traffic on the connection.
If LLC2 Local Acknowledgment is configured, it must be configured on the serial interface of the router on the 3x74 cluster controller side of the connection and on the Token Ring interface of the router on the 37x5 FEP side of the connection. Whether or not Local Acknowledgment is configured, the SNA session extends end-to-end and the SDLC session extends from the router configured with the serial interface to the 3x74 cluster controller. However, the LLC2 session extends from the 37x5 FEP to the router with the Token Ring interface configured. The LLC2 session is locally terminated at that router. A TCP session is then established across the WAN to router on the 3x74 side of the connection.
To configure the router for SDLLC with RSRB and Local Acknowledgment you must perform all the tasks in the "Configure SDLLC with Direct Connection" section earlier in this chapter. In addition, you must perform the following tasks in global configuration mode:
Local Acknowledgment is not supported when the LLC2 device is attached to an Ethernet rather than to a Token Ring.
For an example of how to configure SDLCC with RSRB and Local Acknowledgment, see "Example of SDLLC with RSRB and Local Acknowledgment" later in this chapter.
For more information about configuring RSRB and Local Acknowledgment, see the "Configuring Source-Route Bridging" chapter in this manual and the "Source-Route Bridging Commands" chapter in the Router Products Command Reference publication.
SDLLC support over Ethernet combines Translational Bridging with Ethernet support of 37x5 FEP connections. Figure 1-2 shows SDLLC with Ethernet and Translational Bridging. The 3x75 FEP is attached to Router A through Ethernet. The same router is configured for Translational Bridging, which translates Ethernet packets into Token Ring packets and passes them across the WAN to Router B connected to the 3x74 cluster controller via a serial line. The LLC2 session terminates at the Router B connected to the 3x74 cluster controller. In addition, Router B maintains an SDLC session from itself to the cluster controller.
To increase performance on connections involving SDLLC media translation, you can perform the following tasks:
Generally, the router and the LLC2 device with which it communicates should support the same maximum SDLC I-frame size. The larger this value, the better the line is used, thus increasing performance.
Faster screen updates to 3278-style terminals often result by configuring the Token Ring FEP to send as large an I-frame as possible and then allowing the router to segment the frame into multiple SDLC I-frames.
After the Token Ring FEP has been configured to send the largest possible I-frame, it is best to configure the router to support the same maximum I-frame size. The default is 516 bytes. The maximum value the router can support is 8144 bytes.
To set the largest LLC2 I-frame size, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Specify the largest I-frame size that can be sent or received by the designated LLC2 primary station. | sdllc ring-largest-frame value |
Generally, the router and the SDLC device with which it communicates should support the same maximum SDLC I-frame size. The larger this value, the better the line is utilized, thus increasing performance.
After the SDLC device has been configured to send the largest possible I-frame, you must configure the router to support the same maximum I-frame size. The default is 265 bytes. The maximum value the router can support must be less than the value of the LLC2 largest frame value defined using the sdllc ring-largest-frame command.
To set the largest SDLC I-frame size, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Set the largest I-frame size that can be sent or received by the designated SDLC station. | sdlc sdlc-largest-frame address value |
You can increase the data transfer rate by increasing the SDLC line speed. Use the clockrate command to increase the SDLC line speed on the serial interface. If possible, increase the link speed of the 3x74 to 19.2 kbps on older units, or to 64 kbps on new units.
To increase the SDLC line speed, perform the following tasks in interface configuration mode:
| Task | Command |
|---|---|
| Adjust the clock rate on the serial interface of the SCI and MCI cards to an acceptable bit rate. | clockrate speed |
For information about this command, refer to the "Interface Commands" chapter of the Router Products Command Reference publication.
In addition to adjusting the SDLLC parameters described in this section, you can improve performance on the connection by adjusting the LLC2 and SDLC parameters described in
the chapter "Configuring LLC2 and SDLC Parameters".
Finally, consider this suggestion for IBM host configuration. Change the default MAXOUT (window size) value. Widely used installation guides for IBM equipment show a MAXOUT value of 1 in the VTAM-switched major node for the 3174 PU. Changing this value to 7 improves the performance, because VTAM can send seven frames before requiring an acknowledgment.
This section covers how to monitor connections using SDLLC media translation, as follows:
Perform the following monitoring tasks in EXEC mode:
In show llc2 output, look for the LLC2 connections that correspond to the MAC addresses you assigned to the SDLLC interfaces using the sdllc traddr command. For information about these commands, see the "LLC2 and SDLC Commands" chapter in the Router Products Command Reference publication.
Use the examples in this section to help you understand how to configure SDLLC for your network. The examples provided are as follows:
Figure 24-3 shows a router configuration when the router directly connects the Token Ring and the serial line. The router is configured with SRB.
source-bridge ring-group 100
interface tokenring 0
source-bridge 111 1 100
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdllc traddr 0110.2222.3300 222 2 100
sdllc partner 4000.0122.0001 c1
sdllc xid c1 1720001
Figure 1-4 shows a router configuration when the router directly connects the Token Ring and the serial line but uses RSRB to create a virtual ring 100.
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.1.1
source-bridge remote-peer 100 tcp 131.108.2.2
interface tokenring 0
ip address 131.108.2.2 255.255.255.0
source-bridge 111 1 100
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdllc traddr 0110.2222.3300 8 1 100
sdllc partner 1000.5a7d.8123 c1
sdllc xid c1 17200c1
In Figure 1-5, SDLLC with RSRB connects an FEP and a single 3x74 cluster controller. The host wants to communicate with a single 3174 that its front end processor (FEP) sees on a Token Ring. However, the 3x74 seen by the FEP is in fact SDLC device c1 connected by means of a serial link through a remote router.
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.2
interface tokenring 0
ip address 131.108.1.1 255.255.255.0
source-bridge 10 1 100
interface ethernet 0
ip address 131.108.2.1 255.255.255.0
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.1.1
source-bridge remote-peer 100 tcp 131.108.2.2
interface tokenring 0
ip address 131.108.2.2 255.255.255.0
source-bridge 1 1 100
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdllc traddr 0110.2222.3300 8 1 100
sdllc partner 1000.5a7d.8123 c1
sdllc xid c1 17200c1
In the setup shown in Figure 1-6, Router A needs no SDLLC configuration, Router B has the SDLLC configuration and supports multipoint on the SDLC link with a Modem-Sharing Device (MSD), and Router C is also configured with SDLLC.
For information about the NCP and VTAM system generation (sysgen) parameters that are used in this configuration see the "NCP and VTAM Sysgen Parameters" section later in this chapter.
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1
source-bridge remote-peer 100 tcp 131.108.2.2
source-bridge remote-peer 100 tcp 131.108.2.3
interface tokenring 0
ip address 131.108.1.1 255.255.255.0
source-bridge 10 1 100
interface ethernet 0
ip address 131.108.2.1 255.255.255.0
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1
source-bridge remote-peer 100 tcp 131.108.2.2
source-bridge remote-peer 100 tcp 131.108.2.3
interface ethernet 0
ip address 131.108.2.2 255.255.255.0
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdllc traddr 0110.2222.3300 7 1 100
sdllc partner 1000.5a7d.8123 c1
sdllc xid c1 17200c1
interface serial 1
encapsulation sdlc-primary
sdlc address c2
sdllc traddr 0220.3333.4400 7 1 100
sdllc partner 1000.5a7d.8123 c2 MUST MATCH TIC LOCADD, NOTE 2
sdllc xid c2 17200c2 MUST MATCH VTAM IDBLK/IDNUM, NOTE 4
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1
source-bridge remote-peer 100 tcp 131.108.2.2
source-bridge remote-peer 100 tcp 131.108.2.3
interface ethernet 0
ip address 131.108.2.3 255.255.255.0
interface serial 0
encapsulation sdlc-primary
sdlc address c3
sdllc traddr 0110.2222.3300 9 1 100
sdllc partner 1000.5a7d.8123 c3 MUST MATCH TIC LOCADD, NOTE 2
sdllc xid c3 17200c3 MUST MATCH VTAM IDBLK/IDNUM, NOTE 4
The configuration shown in Figure 1-7 enables Local Acknowledgment for Router B, which means that the LLC session terminates at Router A. However, the LLC2 session between Router A and Router C is not locally acknowledged and terminates at Router C.
For information about the NCP and VTAM system generation (sysgen) parameters that are used in this configuration see the "NCP and VTAM Sysgen Parameters" section later in this chapter.
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1
source-bridge remote-peer 100 tcp 131.108.2.2 local-ack
source-bridge remote-peer 100 tcp 131.108.2.3
!
interface tokenring 0
ip address 131.108.1.1 255.255.255.0
source-bridge 1 1 100
!
interface ethernet 0
ip address 131.108.2.1 255.255.255.0
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1 local-ack
source-bridge remote-peer 100 tcp 131.108.2.2
source-bridge remote-peer 100 tcp 131.108.2.3
source-bridge sdllc local-ack
!
interface ethernet 0
ip address 131.108.2.2 255.255.255.0
!
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdllc traddr 4000.3174.0b0d 7 1 100
sdllc partner 1000.5a7d.8123 c1 MUST MATCH TIC LOCADD, NOTE 2
sdllc xid c1 017200c1 MUST MATCH VTAM IDBLK/IDNUM, NOTE 4
!
interface serial 1
encapsulation sdlc-primary
sdlc address c2
sdllc traddr 0110.2222.3200 8 1 100
sdllc partner 1000.5a7d.8123 c2 MUST MATCH TIC LOCADD, NOTE 2
sdllc xid c2 017200c2 MUST MATCH VTAM IDBLK/IDNUM, NOTE 4
source-bridge ring-group 100
source-bridge remote-peer 100 tcp 131.108.2.1
source-bridge remote-peer 100 tcp 131.108.2.2
source-bridge remote-peer 100 tcp 131.108.2.3
!
interface ethernet 0
ip address 131.108.2.3 255.255.255.0
!
interface serial 0
encapsulation sdlc-primary
sdlc address c3
sdllc traddr 4000.3174.0c00 9 1 100
sdllc partner 1000.5a7d.8123 c3 MUST MATCH TIC LOCADD, NOTE 2
sdllc xid c3 017200c3 MUST MATCH VTAM IDBLK/IDNUM, NOTE 4
The sample system generation (sysgen) parameters in this section show typical NCP and VTAM values that correspond with the Router A, Router B, and Router C configurations shown in
Figure 1-6 and Figure 1-7.
IBM's ACF/NCP uses a function called NTRI (NCP/Token Ring Interconnection) to support Token Ring-attached SNA devices. NTRI also provides translation from Token Ring-attached SNA devices (Physical Units) to switched (dial-up) devices. VTAM provides the resolution for these devices in a Switched Major Node. VTAM treats these devices on NTRI logical lines as switched devices. (For more information consult IBM documentation NCP/SSP/EP Resource Definition Reference, SC30-3448-04.)
Using SDLLC, the Cisco router translates SDLC leased line protocol into Token Ring LLC2 protocol, then the NTRI function in ACF/NCP translates Token Ring LLC2 protocol into an SNA switched protocol.
***************************************************************** *** SAMPLES BASED ON ACF/NCP V5 R4.
*** NOT ALL NCP PARAMETERS ARE SHOWN
*****************************************************************
* *****************************************************************
* OPTIONS DEFINITION STATEMENT
*****************************************************************
NCPOPT OPTIONS NEWDEFN=YES NTRI GENERATION, MUST BE FIRST STMT
*
*****************************************************************
* BUILD MACRO
*****************************************************************
NCPBU BUILD LOCALTO=1.5, NTRI ACK TIMER FOR LOCAL TOKEN RINGS
REMOTTO=2.5, NTRI ACK TIMER FOR REMOTE TOKEN RINGS
USED IN SDLLC CONFIGURATIONS, NOTE 1
*
*****************************************************************
* DYNAMIC RECONFIGURATION POOL SPACE
*****************************************************************
DRPOOL LUDRPOOL NUMTYP2=50 RESERVE 50 LUS ON PU. T2 PUS
*
*****************************************************************
* PHYSICAL GROUP FOR NTRI TIC #1, DEFINITIONS FOR THE TOKEN RING
* ADAPTER TO ESTABLISH PHYSICAL CONNECTIVITY
*****************************************************************
EPHYG GROUP ECLTYPE=PHYSICAL
*
EPHYL LINE ADAPTER=TIC2, TYPE OF ADAPTER
ADDRESS=(16,FULL), INTERNAL FEP TIC ADDRESS
PORTADD=0,
LOCADD=10005a7d8123, TIC ADDRESS, NOTE 2
RCVBUFC=1440,
MAXTSL=2012,
TRSPEED=16 TOKEN RING SPEED
*
EPHYPU PU
*
EPHYLU LU ISTATUS=INACTIVE
*
*****************************************************************
* NTRI PERIPHERAL LOGICAL LINE GROUP, LINE AND PU PAIRS ARE
* GENERATED BY THE AUTOGEN PARAMETER.
*****************************************************************
ELOGG GROUP ECLTYPE=LOGICAL,
PHYPORT=0,
CALL=INOUT,
AUTOGEN=3 ONE PER SDLLC CONTROLLER,
NOTE 3
*****************************************************************
*****************************************************************
* VTAM SWITCHED MAJOR NODE, BASED ON ACF/VTAM V3 R4.
* THE CODING BELOW SUPPORTS DIAL IN OPERATION ONLY. TYPICALLY,
* NTRI IMPLEMENTATIONS USE ONLY DIAL IN. IF DIAL OUT FROM AN
* APPLICATION IS REQUIRED, PATH MACROS MUST BE USED. CONSULT
* THE APPROPRIATE VTAM INSTALLATION REFERENCE MANUAL.
*****************************************************************
VSWITCH VBUILD TYPE=SWNET
*
VPU1 PU ADDR=13, COULD BE ANYTHING (NOT USED)
IDBLK=017, XID PARM, NOTE 4
IDNUM=200c1, XID PARM, NOTE 4
MAXOUT=7,
MAXDATA=265,
MODETAB=AMODETAB,
DLOGMOD=US327X,
PUTYPE=2,
USSTAB=USS327X
*
VLU1A LU LOCADDR=2,
VLU1B LU LOCADDR=3
*
VPU2 PU ADDR=13, COULD BE ANYTHING (NOT USED)
IDBLK=017, XID PARM, NOTE 4
IDNUM=200c2, XID PARM, NOTE 4
MAXOUT=7,
MAXDATA=265,
MODETAB=AMODETAB,
DLOGMOD=US327X,
PUTYPE=2,
USSTAB=USS327X
*
VLU2A LU LOCADDR=2,
VLU2B LU LOCADDR=3
*
VPU3 PU ADDR=13, COULD BE ANYTHING (NOT USED)
IDBLK=017, XID PARM, NOTE 4
IDNUM=200c3, XID PARM, NOTE 4
MAXOUT=7,
MAXDATA=265,
MODETAB=AMODETAB,
DLOGMOD=US327X,
PUTYPE=2,
USSTAB=USS327X
*
VLU3A LU LOCADDR=2,
VLU3B LU LOCADDR=3
*
In these sample definitions:
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