Configuring the LLC2 Data Link Interface

This chapter describes the steps for configuring the Logical Link Control, type 2 (LLC2) data link interface. You may need to configure the LLC2 data link interface if you are configuring source route bridging, Advanced Peer-to-Peer Networking (APPN) routing, data link switching (DLSw), or Synchronous Data Link Control (SDLC).

Logical Link Control, type 2 (LLC2) is a connection-oriented version of the LLC data-link layer protocol used to connect end devices. The LLC2 data link interface can be configured on the bridge/router. These parameters determine the session interaction between the LLC2 end systems and the bridge/router. The default settings should be sufficient for most network configurations.

For more information on LLC2 p-bits (poll bits) and I-frames (information frames) configured in this procedure, see the IBM Token-Ring Network Architecture Reference document.

To configure the LLC2 data link interface, follow these steps:

1 .   Configure the length of time the bridge/router waits for a response of an LLC2 p-bit command, or acknowledgment of an LLC2 I-frame using:

SETDefault !<port> -LLC2 TImerReply = <milliseconds>(5000-60000)

The default is 3000 milliseconds.

2 .   Configure the length of time that the bridge/router will wait before acknowledging the received I-frame using:

SETDefault !<port> -LLC2 TImerAck = <milliseconds>(0-500)

The default is zero.

3 .   Configure the time period that the bridge/router expects to receive a frame from the other end using:

SETDefault !<port> -LLC2 TImerInact = <milliseconds>(3000-180000)

The default is 60,000 milliseconds.

The bridge/router transmits a poll and activates the Reply Timer (configured in step 1) after the specified expiration time.

The TImerInact value should be at least five times the value entered for the TImerReply parameter.

4 .   Define the retry count, or the maximum number of times to retransmit after the reply timer expires using:

SETDefault !<port -LLC2 RetryCount = <retrys>(1-255)

The default is 7.

5 .   Configure the maximum frame size in bytes of the information field using:

SETDefault !<port> -LLC2 MaxFrame = <size>(128-4399)

The default is 1500 bytes.

6 .   Configure the receive window size for I-frames using:

SETDefault !<port> -LLC2 ReceiveWindow = <size>(1-128)

The default is 1.

7 .   Configure the transmit window size for I-frames using:

SETDefault !<port> -LLC2 TransmitWindow = <size>(1-128)

The default is 7.

8 .   Prepare for the number of LLC2 sessions you plan to have using:

SETDefault -SYS CONNectionUsage = [High | Medium | Low]

This command sets up the number of LLC2 and X.25 connection service sessions allowed at one time. The default for this parameter is "High" for systems using the Dual Processor Engine (DPE) and "Low" for all other systems. If the CONNectionUsage is set to Low, the setting may not be enough depending on how many LLC2 sessions you plan to have.

After setting this parameter, you must reboot the system for it to take effect.

You may need to change the setting to medium for some situations. For example, if you have a few LLC2 sessions running on the low setting, and you cannot get additional LLC2 sessions to connect, you may want to change the setting to medium. In addition, if you are accepting many incoming LLC2 tunnel sessions to a bridge/router serving an systems network architecture (SNA) host, you may want to change the setting to medium.

The number of LLC2 sessions possible with each CONNectionUsage setting depends on several factors, including:

• The hardware platform and the amount of available memory

• The number of X.25 connection service sessions being run

For more information on the CONNectionUsage parameter, see the SYS Service Parameters chapter in Reference for Enterprise OS Software.

You can display information about specific LLC2 sessions or a log of LLC2 activity.

To display information regarding LLC2 data link interface sessions, enter:

SHow -LLC2 SESSions

The display is similar to the following:

---------------------------LLC2 Sessions---------------------------

.........LLC2 Active Source Mac Address:%02608C3C36AC..............

Source:%02608C3C36AC Sap:04 Dest:%02608C1A0CE7 Sap:04 Port:!2-ACTIVE RIF: 06F0 (SRF LF=0x38:92&3:258

In this display, "Source" refers to the media access control (MAC) address of the bridge/router where the LLC2 connection originated, and "Destination" refers to the MAC address of the bridge/router where the LLC2 connection is intended to go. For tunneling, the source address is the peer MAC address, and the destination address is the local MAC address that is configured with the TUNnelMAcadd parameter.

The source or destination depends on which tunnel peer bridge/router you are using. For example, if you entered the SHow -LLC2 SESSions command on the destination bridge/router shown in the preceding display, the MAC addresses would be reversed, as shown in the following display:

---------------------------LLC2 Sessions---------------------------

.........LLC2 Active Source Mac Address:%02608C1A0CE7..............

Source:%02608C1A0CE7 Sap:04 Dest:%02608C3C36AC Sap:04 Port:!2-ACTIVE RIF: Transparent Frame

For more information on the parameters in the LLC2 Service, see the LLC2 Service Parameters chapter in Reference for Enterprise OS Software.

You can display a log of LLC2 activity by entering:

SHow -LLC2 Llc2LOG

The log displays a history of the most recent 256 log entries including the following actions:

• Session activation or deactivation

• Session failure

IBM-related services such as DLSw and APPN are affected by parameter settings in the BRidge, SR, and LLC2 Services. NETBuilder token ring ports that send or receive LLC2 or NetBIOS packets must be configured properly to avoid token ring frame copy errors and to allow connectivity. Table 66 shows the required settings in source route (SR), source route transparent (SRT), and transparent bridging environments for each of the IBM-related services. 3Com recommends configuring token ring ports for source route only mode if possible.

In Table 66, tunneling refers to the 3Com proprietary method of LLC2 tunneling, DLSw refers to data link switching, and LNM refers to LAN Net Manager. The settings are shown in abbreviated form. 3Com-recommended configurations are shown in bold.

Table 66 IBM-Related Settings for Token Ring Ports

Services	Port Config- uration	Source Route Bridging (-SR SRB)	Transparent Bridging (-BR TB)	Bridging (-BR CONT)	Route Discovery (-SR RD)	LLC2 CONTrol (-LLC2 CONT)	Frame Copy Errors
Bridging only	SR	SRB	NTB	BR	NoLLC2	Disable	None
Bridging only	SRT	SRB	TB	BR	NoLLC2	Disable	1
Bridging only	T	NSRB	TB	BR	NoLLC2	Disable	*
LNM	SR	SRB	NTB	BR	LLC2	Enable	None
DLSw/ Tunneling	SR	SRB	NTB	NBR | BR	LLC2	Enable	None
DLSw/ Tunneling	SRT	SRB	TB	BR	LLC2	Enable	* 2
DLSw/ Tunneling	T	NSRB	TB	BR	NoLLC2	Enable	*
APPN	SR	SRB	NTB	NBR | BR	LLC2	Disable	None
APPN	SRT	SRB	TB	NBR | BR	LLC2	Disable	*
APPN	T	NSRB	TB	NBR | BR	LLC2	Disable	*
Default Setting	SRT	SRB	TB	NBR	NoLLC2	Disable	None

1 In this configuration, end systems may generate a small number of token-ring MAC frame copy error report packets when the NETBuilder bridge/router is initializing or when it ages out a MAC address from its bridge table. 2 In this configuration it is important for global bridging to be enabled, otherwise the token ring hardware does not filter transparent packets. This can generate many frame copy error reports and adversely effect performance. To prevent forwarding of bridge packets in this configuration, enter the following command: SETDefault -BRidge CONTrol = NoForward. The NoForward parameter allows DLSw and LLC2 tunneling to send and receive LLC2 SNA and NETBios packets, but prevents other packets from bridging.

The row in Table 66 labeled DLSw/Tunneling with port configuration SR represents DLSw or 3Com tunneling in a source-route-only port configuration. The entries in this row expand to the following NETBuilder software configuration syntax:

SETDefault -BRidge CONTrol = Bridge | NoBridge

SETDefault !<port> -SR SrcRouBridge = SrcRouBridge

SETDefault !<port> -BRidge TransparentBridge = NoTransparentBridge

SETDefault !<port> -SR RingNumber = <number> (1-4095)

SETDefault !<port> -SR RouteDiscovery = LLC2

SETDefault !<port> -LLC2 CONTrol = Enable

In this configuration, global bridging is enabled or disabled on one or more token ring ports. Transparent bridging is disabled, source routing and route discovery are configured, and LLC2 is enabled.