Software User's Guide Version 3.3

Configuring and Monitoring LLC Interfaces

This chapter describes how to configure specific LLC interfaces in the router by using either the interface commands or the GWCON interface command.

Logical Link Level can be thought of as a "sub-protocol". It is not accessed directly from either the Talk 6 (configuration) or the Talk 5 (monitoring) environment. Instead, it is accessed from the Token Ring, Point-to-Point (PPP), or Frame Relay protocols by entering an LLC command.

This chapter includes the following sections:

Accessing the Interface Configuration Process
Accessing the Interface Monitoring Process
LLC Monitoring Commands
LLC Configuration Commands

Accessing the Interface Configuration Process

Access the configuration commands for the protocol you wish to configure over LLC:

Token Ring, as described in Configuring IEEE 802.5 Token-Ring Network Interfaces
Point-to-Point, as described in Using Point-to-Point Protocol Interfaces
Frame Relay, as described in Using Frame Relay Interfaces

Each of these prompt levels has an LLC command. Enter LLC to access the LLC configuration commands and perform LCC configuration. When you are finished, enter Exit to return to the prompt level for the protocol you are configuring.

LLC Configuration Commands

LLC configuration is required when you need to pass packets over an SNA network. To enter these commands, you must first enter the LLC configuration environment (see Accessing the Token-Ring Interface Configuration Process).

This section summarizes and then explains all of the LLC configuration commands. These commands, shown in Table 31, enable you to configure LLC when you need to pass packets over a SNA network.

Table 31. LLC Configuration Command Summary

Command Function
? (Help) Displays all the commands available for this command level or lists the options for specific commands (if available). See "Getting Help".
List Displays the selected LLC configuration.
Set Sets the timers associated with LLC, and the size of the transmit and receive windows.
Exit Returns you to the previous command level. See "Exiting a Lower Level Environment".

Command	Function
? (Help)	Displays all the commands available for this command level or lists the options for specific commands (if available). See "Getting Help".
List	Displays the selected LLC configuration.
Set	Sets the timers associated with LLC, and the size of the transmit and receive windows.
Exit	Returns you to the previous command level. See "Exiting a Lower Level Environment".

List

Use the list command to display the current configuration for the LLC.

Syntax:

list

Example:

list
Reply Timer (T1):                 1 seconds
Receive ACK Timer (T2):           100 milliseconds
Inactivity Timer (Ti):            30 seconds
Max Retry value (N2):             8
Rcvd I-frames before ACK (N3):    1
Transmit Window (Tw):             2
Receive Window (Rw):              2
Acks needed to increment Ww (Nw): 1

Reply Timer (T1): This timer expires when the LLC fails to receive a required acknowledgment or response from the other LLC station.
Receive ACK Timer (T2): This timer is used to delay sending of an acknowledgment for a received I-format frame.
Inactivity Timer (Ti): This timer expires when the LLC does not receive a frame for a specified time period. When this timer expires the LLC transmits an RR until the other LLC responds or the N2 retry count is exceeded. Default is 30 seconds.
Max Retry value (N2): The maximum number of retries by the LLC protocol. Default is 8.
Rcvd I-frames before ACK (N3): This value is used with the T2 timer to reduce acknowledgment traffic for received I-frames. This counter sets a specified value and decrements each time an I-frame is received. When this counter reaches 0 or the T2 timer expires, an acknowledgment is sent. Default is 1.
Receive Window (Rw): Indicates the maximum number of unacknowledged sequentially numbered I-frames that an LLC can receive from a remote host.
Transmit Window (Tw): Indicates the maximum number of I-frames that can be sent before receiving an RR.
Acks needed to increment Ww (Nw): This field is set to a default value of 1.

Set

Use the set command to configure the LLC.

Attention: Changing LLC parameters from the defaults can affect how the LLC protocol works.

Syntax:

set: n2-max-retry count
: n3-frames-rcvd-before-ack count
: nw-acks-to-inc-window count
: rw-receive-window count
: t1-reply-timer seconds
: t2-receive-ack-timer seconds
: ti-inactivity-timer seconds
: tw-transmit-window count

n2-max-retry

The maximum number of retries by LLC protocol. For example, N2 is the maximum number of times the LLC transmits an RR without receiving an acknowledgment when the inactivity timer expires. Default is 8. Minimum is 1. Maximum is 127.

Example:

set n2-max-retry
Max Retry value (N2) [8]?

n3-frames_rcvd-before-ack

This value is used with the T2 timer to reduce acknowledgment traffic for received I-frames. Set this counter to a specified value. Each time an I-frame is received, this value decrements. When this counter reaches 0 or the T2 timer expires, an acknowledgment is sent. Default is 1. Minimum is 1. Maximum is 255.

Example:

set n3-frames_rcvd-before-ack
Number I-frames received before sending ACK(N3) [1]?

rw-receive-window

Indicates the maximum number of unacknowledged sequentially numbered I-frames that an LLC can receive from a remote LLC peer. This value must be equal to or less than 127.

Example:

set rw-receive-window
Receive Window (Rw), 127 Max. [2]?

nw-acks-to-inc-ww

This field is set to a default value of 1.

t1-reply-timer

This timer expires when the LLC fails to receive a required acknowledgment or response from the other LLC station. When this timer expires, an RR is sent with the poll bit set and T1 is started again. If the LLC receives no response after the configured maximum number of retries (N2), the link underneath is declared inoperative. Default is 1. Minimum is 1. Maximum is 256.

Example:

set t1-reply-timer
Reply Timer (T1) in sec. [1]?

t2-receive-ack-timer

This timer is used to delay sending of an acknowledgment for a received I-format frame. This timer is started when an I-frame is received. The timer is reset when an acknowledgment is sent. If this timer expires, LLC2 sends an acknowledgment as soon as possible. Set this value so that it is less than that of T1. This insures that the remote LLC2 peer receives the delayed acknowledgment before the T1 timer expires. Default is 1 (100 ms). Minimum is 1. Maximum is 2560.

Example:

set t2-receive-ack-timer
Receive Ack timer (T2) in 100 millisec. [1]?

Note:

If this timer is set to 1 (the default) it will not run (for example, n3-frames_rcvd-before-ack =1).

ti-inactivity-timer

This timer expires when the LLC does not receive a frame for a specified time period. When this timer expires the LLC transmits an RR until the other LLC responds or the N2 retry count is exceeded. Default is 30 seconds. Minimum is 1 second. Maximum is 256 seconds.

Example:

set ti-inactivity-timer
Inactivity Timer (Ti) in sec. [30]?

tw-transmit-window

Sets the maximum number of I-frames that can be sent before receiving an RR. Assuming that the other end of the LLC session can actually receive this many consecutive I-frames, and the router has enough heap memory to keep copies of these frames until an acknowledgment is received, increasing this value may increase the throughput. Default is 2. Minimum is 1. Maximum is 127.

Example:

set tw-transmit-window
Transmit Window (Tw), 127 Max. [2]?

Accessing the Interface Monitoring Process

Access the monitoring commands for the protocol you wish to monitor over LLC:

Token Ring, as described in Configuring IEEE 802.5 Token-Ring Network Interfaces
Point-to-Point, as described in Configuring and Monitoring Point-to-Point Protocol Interfaces
Frame Relay, as described in Configuring and Monitoring Frame Relay Interfaces

Each of these prompt levels has an LLC command. Enter LLC to access the LLC monitoring commands to monitor LCC. When you are finished, enter Exit to return to the prompt level for the protocol you are monitoring.

LLC Monitoring Commands

This section summarizes and then explains all of the LLC monitoring commands. These commands, shown in Table 32, let you monitor the LLC while passing packets over an SNA network.

Table 32. LLC Monitoring Command Summary

Command Function
? (Help) Displays all the commands available for this command level or lists the options for specific commands (if available). See "Getting Help".
Clear-counters Clears all statistical counters.
List Displays interface, SAP, and session information.
Set Allows the user to dynamically configure LLC parameters that are valid for the life of the session.
Exit Returns you to the previous command level. See "Exiting a Lower Level Environment".

Command	Function
? (Help)	Displays all the commands available for this command level or lists the options for specific commands (if available). See "Getting Help".
Clear-counters	Clears all statistical counters.
List	Displays interface, SAP, and session information.
Set	Allows the user to dynamically configure LLC parameters that are valid for the life of the session.
Exit	Returns you to the previous command level. See "Exiting a Lower Level Environment".

Clear-Counters

Use the clear-counters command to clear all the LLC statistical counters.

Syntax:

clear-counters

List

Use the list command to display interface, service access point (SAP), and session information.

Syntax:

list: interface
: sap . . .
: session

interface

Displays all SAPs opened on this interface.

Example:

            list interface
            SAP      Number of Sessions
            F4       1

sap sap_number

Displays information for the specified SAP on the interface.

Example:

list sap
SAP value in hex (0FE) [1]? F4
 
Interface                      0, TKR/0
Reply Timer(T1)                1 sec
Receive ACK Timer (T2)         100 millisec
Inactivity Timer (Ti)          30 sec
MAX Retry Value (N2)           8
MAX I-field Size (N1)          2052
Rcvd I-frames before ACK (N3)  1
Transmit Window Size (Tw)      2
Acks Needed to Inc Ww (Nw)     1
 
Frame                          Xmt   Rcvd
UI-frames                      4     5
TEST-frames                    0     1
XID-frames                     0     0
I-frames                       291   26
RR-frames                      81    291
RNR-frames                     0     0
REJ-frames                     0     0
SABME-frames                   1     0
UA-frames                      0     1
DISC-frames                    0     0
DM-frames                      0     0
FRMR-frames                    0     0
I-frames discarded by LLC            0
I-frames Refused by LLC user         0
 
Cumulative number of sessions        1
Number of active sessions            1
 
Session ID                                          Remote
(int-sap-id)   Local MAC           Remote MAC          SAP   State
00F40000     00:00:C9:08:41:DB   10:00:5A:F1:02:37   F4    OPENED

SAP value in hex (0FE): The SAP value of the session.
Interface: The interface number and type over which the session is running.
Reply Timer (T1): Indicates the time it takes for this timer to expire when the LLC fails to receive an acknowledgment or response from the other LLC station.
Receive ACK Timer (T2): Indicates the time delay the LLC uses before sending an acknowledgment for a received I-frame.
Inactivity Timer (Ti): Indicates the time the LLC waits during inactivity before issuing an RR.
MAX Retry Value (N2): The maximum number of retries by the LLC protocol.
MAX I-field Size (N1): Maximum amount of data (in bytes) allowed in the I-field of an LLC2 frame.
Rcvd I-frame before ACK (N3): Indicates the value that is used with T2 timer to reduce acknowledgment traffic for received I-frames.
Transmit Window Size (Tw): Indicates the maximum number I-frames that can be sent before receiving an RR.
Acks Needed to Inc Ww (Nw): This field is set to a default value of 1.
Frames Xmt and Rcvd: Counter that displays the total number of frame types transmitted (Xmt) and (Rcvd).
I-frames discarded by LLC: Counter that displays the total number of I-frames discarded by the LLC, usually because the sequence number is out of sequence.
I-frames refused by LLC user: Counter that displays the number of I-frames discarded by the software above the LLC. For example, DLSw (Data Link Switching).
Cumulative number of sessions: The total number of sessions that were opened over this SAP.
Number of active sessions: The total number of currently active sessions that are running over the interface.
Session ID (int-sap-id): The session ID for the monitoring interface.
Local MAC: The router's LLC MAC address.
Remote MAC: The remote LLC's MAC address.
Remote SAP: The remote SAP of the LLC connection.
Remote State: The finite state(s) that results from interaction between the LLC peers. There are 21 states that are described below.

Link_Closed: The remote LLC peer is not known to the local LLC peer and is considered as not existing.
Disconnected: The local LLC peer is known to the other peer. This LLC peer can send and receive XID, TEST, SABME, and DISC commands; and XID TEST, UA, and DM responses.
Link_Opening: The state of the local LLC peer after sending a SABME or UA in response to a received SABME.
Disconnecting: The state of the local LLC after sending a DISC command to the remote LLC peer.
FRMR_Sent: The local LLC peer has entered the frame reject exception state and has sent a FRMR response across the link.
Link_Opened: The local LLC peer is in the data transfer phase.
Local_Busy: The local LLC peer is unable to receive additional I-frames.
Rejection: A local LLC peer that has received one or more out-of-sequence I-frames.
Checkpointing: The local LLC peer has sent a poll to the remote LLC peer and is waiting for an appropriate response.
CKPT_LB: A combination of checkpointing and local busy states.
CKPT_REJ: A combination of the checkpointing and rejection states.
Resetting: The local LLC peer has received a SABME and is reestablishing the link.
Remote_Busy: The state that occurs when an RNR is received from the remote LLC peer.
LB_RB: A combination of local_busy and remote_busy states.
REJ_LB: A combination of rejection and local_busy states.
REJ_RB: A combination of rejection and remote_busy states.
CKPT_REJ_LB: A combination of checkpointing, rejection, and local_busy states.
CKPT_CLR: A combination state resulting from the termination of a local_busy condition while the LLC peer is CKPT_LB.
CKPT_REJ_CLR: A combination state resulting from the transfer of an unconfirmed local busy clear while the link station is in the CKPT_REJ_LB state.
REJ_LB_RB: A combination of the rejection, local_busy, and remote_busy states.
FRMR_Received: The local LLC peer has received an FRMR response from the remote LLC peer.

Session

Displays information on the specified LLC session that is open on the interface.

Example:

list session
Session Id: [0]? 00-F4-0000
 
Interface0,                    TKR/0
Remote MAC addr                10:00:5A:F1:02:37
Source MAC addr                00:00:C9:08:35:47
Remote SAP                     F4
Local SAP                      F4
RIF                            (089E 0101 0022 0010)
Access Priority                0
State                          LINK_OPENED
Replay Timer                   1 sec
Receive ACK Timer (T2)         100 millisec
Inactivity Timer (Ti)          30 sec
MAX I-field Size (N1)          2052
MAX Retry Value (N2)           8
Rcvd I-frames before ACK (N3)  1
Transmit Window Size (Tw)      2
Working Transmit Size (Ww)     2
Acks Needed to Inc Ww (Nw)     1
Current Send Seq (Vs)          9
Current Rcv Seq (Vr)           7
Last ACK'd sent frame (Va)     9
No. of frames in ACK pend q    0
No. of frames in Tx pend q     0
Local Busy                     NO
Remote Busy                    NO
Poll Retry count               8
Appl output flow stopped       NO
Send process running           YES
 
Frame                           Xmt   Rcvd
I-frames                        1456  2678
RR-frames                       502   403
RNR-frames                      0     0
REJ-frames                      0     0
I-frames discarded by LLC             0
I-frames Refused by LLC user          0

Session Id: Indicates the session ID number.
Interface: Indicates the number of the interface over which this session is running.
Remote MAC addr: Indicates the MAC address of the remote LLC peer.
Source MAC addr: Indicates the MAC address of the local LLC.
Remote SAP: The remote side SAP of the LLC connection.
Local SAP: The local side SAP of the LLC connection.
RIF: The actual RIF of the frame.
Access Priority: Priority of the packet. 07 for upper layer control.
State: The finite state(s) that results from interaction between the LLC peers. Refer to the list sap command on page *** for more information.
Receive ACK timer (T2): Indicates the time delay the LLC uses before sending an acknowledgment for a received I-frame.
Inactivity timer (Ti): Indicates the time the LLC waits during inactivity before issuing an RR.
MAX I-field size (N1): Maximum size of the data field (in bytes) of a frame. Default is the size of the interface.
MAX Retry Value (N2): The maximum number of times the LLC transmits an RR without receiving an acknowledgment
Rcvd I-frames before ACK (N3): Indicates the value that is used with T2 timer to reduce acknowledgment traffic for received I-frames.
Transmit window size (Tw): Indicates the maximum number of I-frames that can be sent before receiving an RR.
Working transmit size (Ww): The maximum number of I-frames that are sent before receiving an RR.
Acks Needed to Inc Ww (Nw): This field is set to a default value of 1.
Current send seq (Vs): Send state variable (Ns value for the next I-frame to be transferred).
Current Rcv seq (Vr): Receive state variable (next in-sequence Ns to be accepted).
Last ACK'd sent frame (Va): Acknowledged state variable (last valid Nr received).
No. of frames in ACK pend q: Number of transmitted I-frames waiting for acknowledgment.
No. of frames in transmit pend q: Number of frames waiting to be transmitted.
Local Busy: The local side of the LLC connection is sending RNRs.
Remote Busy: The remote side of the LLC is receiving RNRs.
Poll Retry count: Indicates the current value of the retry of the counter (counts down) in the LLC protocol.
Appl output flow stopped: The LLC has told the application to stop giving it outgoing data frames.
Send process running: This process runs concurrently with all other frame actions and takes I-frames in the transmit queue and sends them.
Frames Xmt and Rcvd: Displays the total number of frame types transmitted (Xmt) and (Rcvd).
I-frames discarded by LLC: Counter that displays the total number of I-frames discarded by the LLC, usually because the sequence number is out of sequence.
I-frames refused by LLC user: Counter that displays the number of I-frames discarded by the software above the LLC. For example, DLSw (Data Link Switching).

Set

Use the set command to dynamically configure the LLC parameters on a current LLC session. Any changes that you make to the parameters are effective for the life of session. These parameters are the same as those listed in "Set".

Attention: Changing LLC parameters from the default can affect how the LLC protocol works.

Syntax:

set: n2-max_retry count
: n3-frames-rcvd-before-ack count
: nw-acks-to-inc-ww count
: t1-reply-timer seconds
: t2-receive-ack-timer seconds
: ti-inactivity-timer seconds
: tw-transmit-window seconds

n2-max_retry

n3-frames-rcvd-before-ack

This value is used with the T2 timer to reduce acknowledgment traffic for received I-frames. Set this counter to a specified value. Each time an I-frame is received, this value is decremented. When this counter reaches 0 or the T2 timer expires, an acknowledgment is sent. Default is 1. Minimum is 1. Maximum is 255.

nw-acks-to-inc-ww

This field is set to a default value of 1.

t1-reply-timer

t2-receive-ack-timer

This timer is used to delay sending of an acknowledgment for a received I-format frame. This timer is started when an I-frame is received and reset when an acknowledgment is sent. If this timer expires, LLC2 sends an acknowledgment as soon as possible. Set this value so that it is less than that of T1. This insures that the remote LLC2 peer receives the delayed acknowledgment before the T1 timer expires. Default is 1 (100 ms). Minimum is 1. Maximum is 2560.

Note:

If this timer is set to 1 (the default) it will not run (for example, n3-frames-rcvd-before-ack=1).

ti-inactivity-timer

This timer expires when the LLC does not receive a frame for a specified time period. When this timer expires the LLC transmits an RR until the other LLC responds or the N2 timer expires. Default is 30 seconds. Minimum is 1 second. Maximum is 256 seconds.

tw-transmit-window

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