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LLC2 (IEEE 802.2) type 2 provides connection-oriented service and is widely used in LAN environments, particularly among IBM communication systems connected by Token Ring. Our router supports LLC2 connections over Ethernet, Token Ring, and FDDI.
The LLC2 commands provide operations that support the following features:
SDLC is used as the primary Systems Network Architecture (SNA) link-layer protocol for wide-area network (WAN) links. SDLC defines two types of network nodes: primary and secondary. Primary nodes poll secondary nodes in a predetermined order. Secondaries then transmit if they have outgoing data. When configured as primary and secondary nodes, routers are established as SDLC stations.
The SDLC commands described in this chapter pertain to routers configured as SDLC stations. This is in contrast to a router configured for SDLC Transport where the router is not configured as an SDLC station, but acts as an intermediary, passing SDLC frames between two SDLC stations across a mixed-media, multiprotocol environment.
The SDLC commands support the following features:
Use the commands in this chapter to adjust the router's LLC2 and SDLC parameters. For LLC2 and SDLC parameter configuration information and examples, refer to the " Configuring LLC2 and SDLC" chapter of the Router Products Configuration Guide.
Use the encapsulation sdlc-primary interface configuration command to configure the router as the primary SDLC station.
encapsulation sdlc-primaryThis command has no arguments or keywords.
None
Interface configuration
The encapsulation sdlc-primary or encapsulation sdlc-secondary command must be used to configure an SDLC interface. To use the encapsulation sdlc-primary command, first select the interface on which you want to enable SDLC. Then establish the router as a primary station. Next, assign secondary station addresses to the primary station using the sdlc address command.
SDLC defines two types of network nodes: primary and secondary. Primary nodes poll secondary nodes in a predetermined order. Secondaries then transmit if they have outgoing data. When configured as primary and secondary nodes, our routers are established as SDLC stations.
In the IBM environment, a front-end processor (FEP) is the primary station and establishment controllers (ECs) are secondary stations. In a typical scenario, an EC may be connected to dumb terminals and to a Token Ring network at a local site. At the remote site, an IBM host connects to an IBM FEP, which can also have links to another Token Ring LAN. Typically, the two sites are connected through an SDLC leased line.
If a router is connected to an EC, the router takes over the function of the FEP, and must therefore be configured as a primary SDLC station. If the router is connected to a FEP, the router takes the place of the EC, and must therefore be configured as a secondary SDLC station.
The following example shows how to configure interface serial 0 on your router to have two SDLC secondary stations attached to it through a modem-sharing device (MSD) with addresses C1 and C2:
! enter a global command if you have not already
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdlc address c2
encapsulation sdlc-secondary
sdlc address
show interfaces
Use the encapsulation sdlc-secondary interface configuration command to configure the router as a secondary SDLC station.
encapsulation sdlc-secondaryThis command has no arguments or keywords.
None
Interface configuration
An encapsulation sdlc-primary or encapsulation sdlc-secondary command must be used to configure an SDLC interface. To use the encapsulation sdlc-secondary command, first select the interface on which you want to enable SDLC. Then establish the router as a secondary station. Next, assign secondary station addresses to the primary station using the sdlc address command.
SDLC defines two types of network nodes: primary and secondary. Primary nodes poll secondary nodes in a predetermined order. Secondaries then transmit if they have outgoing data. When configured as primary and secondary nodes, our routers are established as SDLC stations.
In the IBM environment, a front-end processor (FEP) is the primary station and establishment controllers (ECs) are secondary stations. In a typical scenario, an EC may be connected to dumb terminals and to a Token Ring network at a local site. At the remote site, an IBM host connects to an IBM FEP, which can also have links to another Token Ring LAN. Typically, the two sites are connected through an SDLC leased line.
If a router is connected to an EC, the router takes over the function of the FEP, and must therefore be configured as a primary SDLC station. If the router is connected to a FEP, the router takes the place of the EC, and must therefore be configured as a secondary SDLC station.
The following example shows the use of this command:
!
interface serial 0
encapsulation sdlc-secondary
!
encapsulation sdlc-primary
sdlc address
show interfaces
Use the llc2 ack-delay-time interface configuration command to set the amount of time the router waits for an acknowledgment before sending the next set of information frames.
llc2 ack-delay-time milliseconds| milliseconds | Number of milliseconds (ms) the router allows incoming information frames to stay unacknowledged. The minimum is 1 ms. The maximum is 60000 ms. |
3200 ms
Interface configuration
Upon receiving an information frame, each LLC2 station starts a timer. If the timer expires, an acknowledgment will be sent for the frame, even if the llc2 ack-max number of received frames has not been reached. Experiment with the value of the llc2 ack-delay-time command to determine the configuration that balances acknowledgment network overhead and quick response time (by receipt of timely acknowledgments).
Use this command in conjunction with the llc2 ack-max command to determine the maximum number of information frames the router can receive before sending an acknowledgment.
In the following example, the router allows a 100-ms delay before I-frames must be acknowledged:
! enter a global command, if you have not already
interface tokenring 0
! sample ack-max command
llc2 ack-max 3
! allow a 100 millisecond delay before I-frames must be acknowledged
llc2 ack-delay-time 100
At time 0, two information frames are received. The llc2 ack-max amount of three has not been reached, so no acknowledgment for these frames is sent. If a third frame, which would force the router to send an acknowledgment, is not received in 100 ms, an acknowledgment will be sent anyway, because the llc2 ack-delay timer expire. At this point, because all frames are acknowledged, the counter for the ack-max purposes will be reset to zero.
llc2 ack-max
show llc2
Use the llc2 ack-max interface configuration command to control the maximum amount of information frames the router can receive before it must send an acknowledgment.
llc2 ack-max packet-count| packet-count | Maximum number of information frames the router will receive before sending an acknowledgment. The minimum is 1. The maximum is 127. |
3
Interface configuration
An LLC2-speaking station can send only a predetermined number of frames before it must wait for an acknowledgment from the receiver. If the receiver waits until receiving a large number of frames before acknowledging any of them, and then acknowledges them all at once, it reduces overhead on the network.
For example, an acknowledgment for five frames can specify that all five have been received, as opposed to sending a separate acknowledgment for each frame. To keep network overhead low, make this parameter as large as possible.
However, some LLC2-speaking stations expect this to be a low number. Some NetBIOS-speaking stations expect an acknowledgment to every frame. Therefore, for these stations, this number is best set to 1. Experiment with this parameter to determine the best configuration.
In the following example, the router is configured to receive up to seven frames before it must send an acknowledgment. Seven frames is the maximum allowed by SNA before a reply must be received:
! enter a global command, if you have not already
interface tokenring 0
! receive up to seven frames before sending an acknowledgment
llc2 ack-max 7
! sample delay-time command
llc2 ack-delay-time 100
llc2 ack-delay-time
llc2 local-window
show llc2
Use the llc2 idle-time interface configuration command to control the frequency of polls during periods of idle time (no traffic).
llc2 idle-time milliseconds| milliseconds | Number of milliseconds (ms) that can pass with no traffic before the LLC2 station sends a Receiver Ready frame. The minimum is 1 ms. The maximum is 60000 ms. |
10000 ms
Interface configuration
Periodically, when no information frames are being transmitted during an LLC2 session, LLC2 stations are sent a Receiver Ready frame to indicate they are available. Set the value for this command low enough to ensure a timely discovery of available stations, but not too low, or you will create a network overhead with too many Receiver Ready frames.
In the following example, the router waits 20000 ms before sending a Receiver Ready ("are you there") frame:
! enter a global command, if you have not already
interface tokenring 0
! wait 20000 ms before sending receiver-ready frames
llc2 idle-time 20000
llc2 tbusy-time
llc2 tpf-time
show llc2
Use the llc2 local-window interface configuration command to control the maximum number of information frames the router sends before it waits for an acknowledgment.
llc2 local-window packet-count| packet-count | Maximum number of information frames that can be sent before the router must wait for an acknowledgment. The minimum is 1. The maximum is 127. |
7
Interface configuration
An LLC2-speaking station can send only a predetermined number of frames before it must wait for an acknowledgment from the receiver. Set this number to the maximum value that can be supported by the stations with which the router communicates. Setting this value too large can cause frames to be lost, because the receiving station may not be able to receive all of them.
In the following example, the router will send as many as 30 information frames through the tokenring 1 interface before it must receive an acknowledgment:
! enter a global command, if you have not already
interface tokenring 1
llc2 local-window 30
llc2 ack-max
show llc2
Use the llc2 n2 interface configuration command to control the amount of times the router retries sending unacknowledged frames or repolls remote busy stations.
llc2 n2 retry-count| retry-count | Number of times the router retries operations. The minimum is 1. The maximum is 255. |
8
Interface configuration
An LLC2 station must have some limit to the number of times it will resend a frame when the receiver of that frame has not acknowledged it. After the router is told that a remote station is busy, it will poll again based on the retry-count value. When this retry count is exceeded, the LLC2 station terminates its session with the other station. Set this parameter to a value that balances between frame checking and network performance.
In the following example, the router will resend a frame up to four times through interface tokenring 1 before it must receive an acknowledgment. Because you generally do not need to change the retry limit, this example shows you how to reset the limit to the default of 8:
! enter a global command, if you have not already
!
interface tokenring 1
! retry value of 8
llc2 n2 8
llc2 t1-time
llc2 trej-time
llc2 tbusy-time
show llc2
Use the llc2 t1-time interface configuration command to control the amount of time the router will wait before resending unacknowledged information frames.
llc2 t1-time milliseconds| milliseconds | Number of milliseconds (ms) the router waits before resending unacknowledged information frames. The minimum is 1 ms. The maximum is 60000 ms. |
1000 ms
Interface configuration
Use in conjunction with the llc2 n2 command to provide a balance of network monitoring and performance. Ensure that enough time is allowed to account for the round trip between the router and its LLC2-speaking stations under heavy network loading conditions.
In the following example, the router will wait 4000 ms before resending an unacknowledged frame through tokenring 2:
! enter a global command, if you have not already
!
interface tokenring 2
! wait 4000 ms before retransmitting a frame through tokenring 2
llc2 t1-time 4000
llc2 n2
llc2 tpf-time
llc2 xid-retry-time
show llc2
Use the llc2 tbusy-time interface configuration command to control the amount of time the router waits until repolling a busy remote station.
llc2 tbusy-time milliseconds| milliseconds | Number of milliseconds (ms) the router waits before repolling a busy remote station. The minimum is 1 ms. The maximum is 60000 ms. |
9600 ms
Interface configuration
An LLC2 station has the ability to tell others that it is temporarily busy, so the other stations will not attempt to send any new information frames. The frames sent to indicate this are called Receiver Not Ready (RNR) frames. Change the value of this parameter only to increase the value for LLC2-speaking stations that have unusually long busy periods before they clear their busy status. Increasing the value will prevent the stations from timing out.
In the following example, the router will wait up to 12000 ms before attempting to poll a remote station through tokenring 0 to learn the station's status:
! enter a global command, if you have not already
!
interface tokenring 0
! wait 12000 ms before polling a station through tokenring 0
llc2 tbusy-time 12000
llc2 n2
llc2 idle-time
show llc2
Use the llc2 tpf-time interface configuration command to set the amount of time the router waits for a final response to a poll frame before resending the poll frame.
llc2 tpf-time milliseconds| milliseconds | Number of milliseconds (ms) the router waits for a final response to a poll frame before resending the poll frame. The minimum is 1 ms. The maximum is 60000 ms. |
1000 ms
Interface configuration
When sending a command that must receive a response, a poll bit is sent in the frame. This is the receiving station's clue that the sender is expecting some response from it, be it an acknowledgment of information frames or an acknowledgment of more administrative tasks, such as starting and stopping the session. Once a sender gives out the poll bit, it cannot send any other frame with the poll bit set until the receiver replies with a frame containing a final bit set. If the receiver is faulty, it may never return the final bit to the sender. Therefore, the sender could be waiting for a reply that will never come. To avoid this problem, when a poll-bit-set frame is sent, a transmit-poll-frame (TPF) timer is started. If this timer expires, the router assumes that it can send another frame with a poll bit.
Usually, you will not want to change this value. If you do, the value should be larger than the T1 time, set with the llc2 t1-time command. The T1 time determines how long the router waits for receipt of an acknowledgment before sending the next set of frames.
While you generally will not want to change the transmit-poll-frame time, this example sets the TPF time to 3000 ms. Because the TPF time should be larger than the LLC2 T1 time, this example shows the TPF time as double the LLC2 T1 time:
! enter a global command, if you have not already
!
interface tokenring 0
! send a poll bit set through tokenring 0 after a 3000 ms delay
llc2 tpf-time 3000
! wait 1500 ms for an acknowledgment before resending I-frames
llc2 t1-time 1500
llc2 t1-time
llc2 idle-time
llc2 n2
show llc2
Use the llc2 trej-time interface configuration command to control the amount of time a router waits for a correct frame after sending a reject (REJ) command to the remote LLC2 station.
llc2 trej-time milliseconds| milliseconds | Number of milliseconds (ms) the router waits for a resend of a rejected frame before sending a reject command to the remote station. The minimum is 1 ms. The maximum is 60000 ms. |
3200 ms
Interface configuration
When an LLC2 station sends an information frame, a sequence number is included in the frame. The LLC2 station that receives these frames will expect to receive them in order. If it does not, it can reject a frame and indicate which frame it is expecting to receive instead. Upon sending a reject, the LLC2 station starts a reject timer. If the frames are not received before this timer expires, the session is disconnected.
In the following example, the router will wait up to 1000 ms to receive a previously rejected frame before resending its reject message to the station that sent the frame:
! enter a global command, if you have not already
interface tokenring 0
! wait 1000 ms before resending a reject message through tokenring 0
llc2 trej-time 1000
llc2 n2
show llc2
Use the llc2 xid-neg-val-tim interface configuration command to control the frequency of exchange of identification (XID) transmissions by the router.
llc2 xid-neg-val-time milliseconds| milliseconds | Number of milliseconds (ms) after which the router sends XID frames to other LLC2-speaking stations. The minimum is 0 ms. The maximum is 60000 ms. |
0 ms
Interface configuration
Do not change the llc2 xid-neg-val-time parameter unless requested by your technical support representative.
LLC2-speaking stations can communicate exchange of identification (XID) frames to each other. These frames identify the stations at a higher level than the MAC address and also can contain information about the configuration of the station. These frames are typically sent only during setup and configuration periods when it is deemed that sending them is useful. The greatest frequency at which this information is transferred is controlled by this timer.
The following example shows how to reset the frequency of XID transmissions to the default of
0 ms:
! enter a global command, if you have not already
!
interface tokenring 0
! set the frequency of XID transmissions to 0
llc2 xid-neg-val-time 0
llc2 xid-retry-time
show llc2
Use the llc2 xid-retry-time interface configuration command to set the amount of time the router waits for a reply to exchange of identification (XID) frames before dropping the session.
llc2 xid-retry-time milliseconds| milliseconds | Number of milliseconds (ms) the router waits for a reply to XID frame before dropping a session. The minimum is 1 ms. The maximum is 60000 ms. |
60000 ms
Interface configuration
Set this value greater than the value of the T1 time, or the time the router waits for an acknowledgment before dropping the session. T1 time is set with the llc2 t1-time command.
The following example sets the router to wait up to 60000 ms for a reply to XID frames it sent to remote stations (which resets the value to its default):
! enter a global command, if you have not already
interface tokenring 0
! wait 60000 ms for a reply to XID frames
llc2 xid-retry-time 60000
llc2 xid-neg-val-time
llc2 t1-time
show llc2
Use the sdlc address interface configuration command to assign a set of secondary stations attached to the serial link. Use the no form of this command to remove an assigned secondary station.
sdlc address hexbyte| hexbyte | Hexadecimal number (base 16) indicating the address of the serial link. |
None
Interface configuration
Before using this command, first select the interface on which you want to enable SDLC. Then establish the router as a primary station with the encapsulation sdlc-primary command. Next, assign secondary station addresses to the primary station using the sdlc address command. The addresses are given in hexadecimal (base 16) and are given one per line.
The following example shows how to configure interface serial 0 to have two SDLC secondary stations attached to it through a modem-sharing device (MSD) with addresses C1 and C2:
interface serial 0
encapsulation sdlc-primary
sdlc address c1
sdlc address c2
encapsulation sdlc-primary
encapsulation sdlc-secondary
show interfaces
Use the sdlc fair-poll-timer interface configuration command to control the maximum time that a primary SDLC station can send output to a secondary SDLC station before polling for input. Use the no form of this command to retrieve the default value of 500 ms.
sdlc fair-poll-timer milliseconds| milliseconds | Number of milliseconds (ms) that the router has for uninterrupted sending of output. The minimum is 100 ms. The maximum is 10000 ms. |
500 ms
Interface configuration
As is typical for the primary station of an SDLC connection, output from the primary to any of the secondary stations is given a higher priority than receiving input from any of them. The fair-poll-timer indicates the maximum time that can elapse before output from the primary is no longer given that priority and the next poll of the next secondary station is attempted.
Increasing the poll-timer allows the user's screen to be updated more quickly, but may increase the amount of time it takes before the user receives data.
The following example specifies that the router can send output to any secondary station for
2000 ms through interface serial 4 before polling for input must begin:
! enter a global command, if you have not already
interface serial 4
no ip address
! use stun encapsulation
encapsulation stun
! establish stun group 4 on interface serial 4
stun group 4
stun sdlc-role primary
! send output for 2000 ms before polling for input must begin
sdlc fair-poll-timer 2000
sdlc poll-limit-value
sdlc poll-pause-timer
show interfaces
Use the sdlc frmr-disable interface configuration command to indicate that secondary stations on a particular serial link do not support Frame Rejects (FRMRs) or error indications. Use the no form of this command to specify that the secondary station does support FRMRs.
sdlc frmr-disableThis command has no arguments or keywords.
Support of FRMRs or error indications
Interface configuration
FRMRs are error indications that can be sent to an SDLC station indicating that a protocol error has occurred. Not all SDLC stations support FRMRs. If this command is enabled, when the router receives an error, it drops the line by sending a disconnect request to the remote station.
In the following example, the router is set to drop the serial line when it receives a protocol error:
!
interface serial 0
sdlc frmr disable
!
show interfaces
Use the sdlc holdq interface configuration command to control the maximum number of packets that can be held in a buffer before being transmitted to a remote SDLC station.
sdlc holdq address queue-size| address | SDLC address for which you are specifying a queue size. |
| queue-size | Router's local send window size. The minimum is 1. The maximum is none. |
12
Interface configuration
This command is particularly useful with the SDLLC feature that allows an LLC2-speaking SNA station on a Token Ring to communicate with an SDLC-speaking SNA station on a serial link. Frame sizes and window sizes on Token Rings are often much larger than those acceptable for serial links. The fact that serial links are often much slower than Token Rings often makes this problem worse. Therefore, temporary backlogs can exist in periods of high data transfer from the Token Ring station to the serial station. A buffer creates a holding place for backlogged frames awaiting transmission on the serial link. This command is specified for each SDLC address, and therefore, for each SDLC secondary station on the serial link.
The following example shows how to change the output hold queue length to 30 frames on an SDLC station of address c1 off serial 0:
! enter a global command, if you have not already
!
interface serial 0
! use SDLC encapsulation
encapsulation sdlc-primary
! establish address of SDLC station off serial 0 as c1
sdlc address c1
! change the output hold queue length to 30 frames on the SDLC station
sdlc holdq c1 30
show interfaces
Use the sdlc k interface configuration command to set the window size in order to control the maximum number of information frames a router receives before sending an acknowledgment.
sdlc k window-size| window-size | Router's local send window size. The minimum is 1 frame. The maximum is 7 frames. |
7 bits
Interface configuration
When the router is communicating with SDLC, it must have a parameter that controls the maximum number of information frames it will receive before the other end must stop sending and wait for an acknowledgment. The k parameter controls this window of acceptable frames. Use this command in conjunction with the sdlc n1 command to create a balance between frame checking and network performance.
In the following example, the router can send up to five frames before it must receive an acknowledgment:
! enter a global command, if you have not already
!
interface tokenring 0
!send up to 5 frames, then wait for acknowledgment
sdlc k 5
sdlc n1
show interfaces
Use the sdlc n1 interface configuration command to control the maximum size of an incoming frame.
sdlc n1 bit-count| bit-count | Number indicating bit size. Frames that exceed this size are rejected. The minimum is 1 bit. The maximum is 12000 bits. |
12000 bits
Interface configuration
Use with the sdlc k command to reduce network overhead while continuing to check frame transmission.
In the following example, the router rejects frames larger than 10000 bits:
! enter a global command, if you have not already
!
interface tokenring 0
! reject frames larger than 10000 bits
sdlc n1 10000
sdlc k
show interfaces
Use the sdlc n2 interface configuration command to determine the number of times that a router resends a frame before terminating the SDLC session.
sdlc n2 retry-count| retry-count | Number of retry attempts. When this number is exceeded, the SDLC station terminates its session with the other station. The minimum is 1. The maximum is 255. |
20 retries
Interface configuration
Use with the sdlc t1 command to reduce network overhead while continuing to check transmission.
In the following example, the router is set to drop an SDLC station after five unsuccessful attempts to receive an acknowledgment for a frame:
!
interface serial 0
sdlc n2 5
!
sdlc t1
show interfaces
Use the sdlc poll-limit-value interface configuration command to control how many times a single secondary station can be polled for input before the next station must be polled. Use the no form of this command to retrieve the default value.
sdlc poll-limit-value count| count | Number of times the router can poll one secondary station before proceeding to the next station. The minimum is 1. The maximum is 10. |
1
Interface configuration
As is typical for the primary station of an SDLC connection, if a secondary station sends its full possible window of input to the primary router, the router immediately will repoll the same secondary for more data in an attempt to capture the complete transaction at one time. The sdlc poll-limit-value command indicates how many times this can happen before the next station in the poll loop must be polled.
Increasing the value allows for smoother transaction processing but can delay polling of other stations or giving output to other stations.
The following example specifies that the router can be polled two times before the next station in the poll list must be polled:
! enter a global command, if you have not already
interface serial 4
no ip address
! use stun encapsulation
encapsulation stun
! establish stun group 4 on interface serial 4
stun group 4
stun sdlc-role primary
! poll the router up to two times before polling the next station
sdlc poll-limit-value 2
sdlc fair-poll-timer
sdlc poll-pause-timer
show interfaces
Use the sdlc poll-pause-timer interface configuration command to control how long the router pauses between sending each poll frame to secondary stations on a single serial interface. Use the no form of this command to retrieve the default value.
sdlc poll-pause-timer milliseconds| milliseconds | Number of milliseconds (ms) that the router waits before sending the poll frame to a single serial interface. This is a number in the range 1 to 10000. The default is 10 milliseconds. |
10 milliseconds
Interface configuration
As is typical for the primary station of an SDLC connection, the router generates polls periodically to each of the secondary stations to solicit their input. After polling each station on a single serial interface, the router will pause before beginning to poll the next station.
Because the secondaries cannot transmit data until they are polled, increasing this timer can increase response time to the users. However, making this parameter too small can flood the serial link with unneeded polls and require the secondary stations to spend wasted CPU time processing them.
In the following example, the router pauses 2000 ms before sending a series of poll frames through interface serial 4:
! enter a global command, if you have not already
interface serial 4
no ip address
! use STUN encapsulation
encapsulation stun
! establish stun group 4 on interface serial 4
stun group 4
!
stun sdlc-role primary
! wait 2000 ms before sending each series of poll frames
sdlc poll-pause-timer 2000
sdlc fair-poll-timer
sdlc poll-limit-value
show interfaces
Use the sdlc poll-wait-timeout interface configuration command when the router has been configured for Local Acknowledgment and some form of SDLC communication (SDLLC or STUN, for example), to specify the interval the router will wait for polls from a primary node before timing out that connection.
sdlc poll-wait-timeout interval| interval | Number of milliseconds (ms) the router will wait for a poll from the primary station before timing out the connection to the primary station. The minimum is 10 ms. The maximum is 64000 ms. |
10000 ms
Interface configuration
This command can be used on an interface that has been configured as a secondary node, but is not to be used on an interface that has been configured as a primary node.
In a locally acknowledged multidrop environment, the polls the primary node sends to the router can be delayed because the primary node is busy polling other secondary nodes. In such situations, this command can be used to extend the timeout, thus reducing the likelihood the router times out the connection to the primary node.
The following example specifies that the local router will wait an interval of 63000 ms for a poll from a primary station before timing out:
! sample stun peer-name global command
stun peer-name 150.136.134.86
! sample protocol-group command
stun protocol-group 4 sdlc
!
interface serial 0
! sample ip address command
no ip address
! sample encapsulation stun command
encapsulation stun
! place interface serial0 in previously defined STUN group 4
stun group 4
! must enter the next command to use the sdlc poll-wait-timeout command
stun sdlc-role secondary
! set timeout period for polls from primary station to 63000 ms.
sdlc poll-wait-timeout 63000
! list the addresses of the sdlc stations on the link
sdlc address C1
sdlc address C2
! provide stun route command
stun route address C2 tcp 150.136.134.58
stun route address C1 tcp 150.136.134.58
sdlc fair-poll-timer
sdlc poll-limit-value
sdlc poll-pause-time
Use the sdlc slow-poll interface configuration command to enable the slow-poll capability of the router as a primary SDLC station. Use the no form of this command to disable slow-poll capability.
sdlc slow-pollThis command has no arguments or keywords.
Disabled
Interface configuration
You can use this command to improve the performance of a multidropped SDLC configuration when one or more of the secondary stations are inactive.
When slow-poll is enabled, if the router acting as a primary station detects that a secondary SDLC station is not responding, it polls that secondary SDLC station less frequently. The router spends less time waiting for the inactive secondary station to respond, thereby minimizing the performance degradation on the active secondary SDLC stations on the multidropped line.
In the following example, the slow-poll capability is enabled for the router:
!
interface serial 0
sdlc slow-poll
!
sdlc fair-poll-timer
sdlc poll-limit-value
sdlc poll-pause-timer
show interfaces
Use the sdlc t1 interface configuration command to control the amount of time the router waits for an acknowledgment to a frame or sequence of frames.
sdlc t1 timeout| timeout | Number of milliseconds (ms) that the router waits. The minimum is 1 ms. The maximum is 64000 ms. |
3000 ms
Interface configuration
When an SDLC station sends a frame, it waits for an acknowledgment from the receiver that the frame has been received. The sending station cannot wait indefinitely for a response. When the frame is sent, a timer is started. To be consistent with the original specification of SDLC, this timer is called the T1 timer and is controlled by this parameter. If this timer reaches its limit before the acknowledgment is received, the router will try again and resend the frame.
In the following example, the router waits up to 4000 ms for a reply to a frame or sequence of frames:
! enter a global command, if you have not already
interface tokenring 0
sdlc t1 4000
sdlc n2
show interfaces
Use the show interfaces EXEC command to display the SDLC information for a given SDLC interface.
show interfacesThis command has no arguments or keywords.
EXEC
The following is sample output from the show interfaces command for an SDLC primary interface supporting the SDLLC function:
router# show interfaces
Serial 0 is up, line protocol is up
Hardware is MCI Serial
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation SDLC-PRIMARY, loopback not set
Timers (msec): poll pause 100 fair poll 500. Poll limit 1
[T1 3000, N1 12016, N2 20, K 7] timer: 56608 Last polled device: none
SDLLC [ma: 0000.0C01.14--, ring: 7 bridge: 1, target ring: 10
largest token ring frame 2052]
SDLC addr C1 state is CONNECT
VS 6, VR 3, RCNT 0, Remote VR 6, Current retransmit count 0
Hold queue: 0/12 IFRAMEs 77/22 RNRs 0/0 SNRMs 1/0 DISCs 0/0
Poll: clear, Poll count: 0, chain: p: C1 n: C1
SDLLC [largest SDLC frame: 265, XID: disabled]
Last input 00:00:02, output 00:00:01, output hang never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
Five minute input rate 517 bits/sec, 30 packets/sec
Five minute output rate 672 bits/sec, 20 packets/sec
357 packets input, 28382 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
926 packets output, 77274 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets, 0 restarts
2 carrier transitions
Table 1-1 shows the timer fields relevant to all SDLC connections.
| Field | Description |
|---|---|
| Timers (msec): | Lists the timers and their current values. |
| poll pause, fair poll, Poll limit | Current values of these timers, as described in the individual command sections in this chapter. |
| T1, N1, N2, K | Current values for these timers, as described in the individual command sections in this chapter. |
Table 1-2 shows other data given for each SDLC secondary station configured to be attached to this interface.
| Field | Description |
|---|---|
| addr | Address of this secondary SDLC station. |
| state is | Current state of this connection. The possible values are:
|
|
VS | Sequence number of the next information frame this station sends. |
| VR | Sequence number of the next information frame from this secondary that this station expects to receive. |
| Remote VR | Last frame transmitted by this station that has been acknowledged by the other station. |
| Current retransmit count | Number of times the current I-frame or sequence of I-frames has been retransmitted. |
| Hold queue: | Number of frames in hold queue/Maximum size of hold queue. |
| IFRAMEs, RNRs, SNRMs,
DISCs | Sent/received count for these frames. |
| Poll: | "Set" if this router has a poll outstanding to the secondary; "clear" if it does not. |
| Poll count: | Number of polls, in a row, given to this secondary station at this time. |
| chain: | Shows the previous (p) and next (n) secondary address on this interface in the round robin loop of polled devices. |
encapsulation sdlc-primary
encapsulation sdlc-secondary
sdlc fair-poll-timer
sdlc frmr-disable
sdlc holdq
sdlc n1
sdlc n2
sdlc poll-limit-value
sdlc poll-pause-timer
Use the show llc2 EXEC command to display the LLC2 connections active in the router.
show llc2This command has no arguments or keywords.
EXEC
The following is sample output from the show llc2 command:
router# show llc2
TokenRing0 DTE=1000.5A59.04F9,400022224444 SAP=04/04, State=NORMAL
V(S)=5, V(R)=5, Last N(R)=5, Local window=7, Remote Window=127
ack-max=3, n2=8, Next timer in 7768
xid-retry timer 0/60000 ack timer 0/1000
p timer 0/1000 idle timer 7768/10000
rej timer 0/3200 busy timer 0/9600
ack-delay timer 0/3200
CMNS Connections to:
Address 1000.5A59.04F9 via Ethernet2
Protocol is up
Interface type X25-DCE RESTARTS 0/1
Timers: T10 1 T11 1 T12 1 T13 1
The display includes a CMNS addendum, indicating LLC2 is running with CMNS. When LLC2 is not running with CMNS, the show llc2 command does not display a CMNS addendum.
Table 1-3 describes significant fields shown in the display.
| Field | Description |
|---|---|
| TokenRing0 | Name of interface on which the session is established. |
| DTE=1000.5A59.04F9, 400022224444 | Address of the station to which the router is talking on this session. (The router's address is the MAC address of the interface on which the connection is established, except when Local Acknowledgment or SDLLC is used, in which case the address used by the router is shown as in this example, following the DTE address and separated by a comma.) |
| SAP=04/04 | The other station's and the router's (remote/local) Service Access Point for this connection. The SAP is analogous to a "port number" on the router and allows for multiple sessions between the same two stations. |
| State=NORMAL | The current state of the LLC2 session. The possible values are:
|
|
V(S)=5 | Sequence number of the next information frame this station will send. |
| V(R)=5 | Sequence number of the next information frame this station expects to receive from the other station. |
| Last N (R)=5 | Last sequence number of this station's transmitted frames acknowledged by the remote station. |
| Local Window=7 | Number of frames this station may send before requiring an acknowledgment from the remote station. |
| Remote Window=127 | Number of frames this station can accept from the remote. |
| ack-max=3, n2=8 | Value of these parameters, as given in the previous configuration section. |
| Next timer in 7768 | Number of milliseconds before the next timer, for any reason, goes off. |
| xid-retry timer 0/60000.... | A series of timer values in the form of next-time/time-between, where "next-time" is the next time, in milliseconds, that the timer will wake, and "time-between" is the time, in milliseconds, between each timer wakeup. A "next-time" of zero indicates that the given timer is not enabled, and will never wake. |
| CMNS Connections to: | List of values that affect the interface if CMNS is enabled. |
| Address 1000.5A59.04F9 via Ethernet2 | MAC address of remote station. |
| Protocol is up | Up indicates the LLC2 and X.25 protocols are in a state where incoming and outgoing Call Requests can be made on this LLC2 connection. |
| Interface type X25-DCE | One of X25-DCE, X25-DTE, or X25-DXE (both DTE and DCE). |
| RESTARTS 0/1 | Restarts sent/received on this LLC2 connection. |
| Timers: | T10, T11, T12, T13 (or T20, T21, T22, T23 for DTE); these are Request packet timers. These are similar in function to X.25 parameters of the same name. |
llc2 ack-delay-time
llc2 ack-max
llc2 idle-time
llc2 local window
llc2 n2
llc2 t1-time
llc2 tbusy-time
llc2 tpf-time
llc2 trej-time
llc2 xid-neg-val-time
llc2 xid-retry-time
|
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