Checking the Datalink Layer

If the problem is not at the physical layer, the next thing to check is the Solstice X.25 software and configuration. The most important thing is to try and work out in which layer--X.25, LAPB, LLC2, or WAN--the problem originates. In general, you should check the following:

• Check the link and packet layers are up--use x25stat.

• Observe connection attempts and obtain clearing causes and diagnostic codes--use x25trace.

• Log protocol activity--use the strace command and the strerr daemon.

• Obtain an ASCII record of the values of the parameters for all of the layers in your X.25 configuration-- use the x25info utility, in /opt/SUNWconn/bin. This is particularly useful when you need to send a description of your configuration to your support provider.

Using one or more of these diagnostic tools, you can usually obtain sufficient information to diagnose and correct your communications problem.

Obtaining Packet and Link-Level Traces

Use /opt/SUNWconn/bin/x25trace command to capture information about each packet and/or frame sent and received by Solstice X.25.

You can specify the layer you want to trace, the interface you want to trace, and the destination you want to trace. This lets you narrow down the information you receive.

The x25trace command takes the form shown below:

# /opt/SUNWconn/bin/x25trace [options] [-i interface] filter_expression 

You must run it as root, in the foreground. If you want to capture its output in a file, use standard Unix redirection to do so. (This is useful if you intend to contact your local technical support representative for help.) x25trace runs until you enter a Ctrl-C.

You can use specific MAC addresses as filters. For example, you can enter a command that has the effect of saying, "Trace all packets that travel over interface A between address 1 and address 2." Such commands can extend beyond the width of a command line. In this case, use the backslash (\) continuation character to go beyond a single line.

Table 11-1 lists the devices x25trace supports:

The following options are available. They are supported by all of the devices.

-a

By default, x25trace displays the user data in hexadecimal for the highest protocol specified. This option tells x25trace to only display the number of bytes of user data and not display the data in hexadecimal. For example, if you enter:

hostname# x25trace -a -i /dev/llc2 x25

x25trace displays only the number of bytes in X.25 packets sent and received over the llc0 interface.

-l number

Specifies the link on which x25trace is to trace packets. By default, x25trace traces on all links and prints the link number in the traced information. (This option is useful only in the situation in which you have multiple links.)

-u

This option causes x25trace to buffer display output line-by-line, instead of the default operation of packet-by-packet.

-x

This option causes x25trace to display entire packets in hexadecimal, in addition to its default operation of decoding the packet. This option is useful in troubleshooting malformed packets. With such packets, you often see an error message starting with two asterisks (**).

You can use the following filter expressions in an x25trace command line:

betweenmac

Trace only the packets or frames passing between the 802.x MAC addresses you specify.

dstmac

Trace only the packets or frames that have a destination address that is the MAC address you specify.

lapb (or hdlc)

Trace only LAPB frames.

mac

Trace packets and frames to/from the MAC address you specify. Use only when tracing on a LAN interface.

multicast

Trace only LLC2 packets that have multicast addresses.

pdu_in

Trace only incoming Protocol Data Units (PDUs).

pdu_out

Trace only outgoing Protocol Data Units (PDUs).

srcmac

Trace only the packets or frames that have a source address that is the MAC address you specify.

x25

Trace only X.25 Packet Layer Protocol packets.

x25lcn [+|num>]

Used with a plus sign (+), this expression means trace only the packets that travel on the next logical channel set up. Used with a number, it means trace only the packets that travel on the logical channel identified by num.

x25trace Examples

Below are some examples of using x25trace for tracing incoming and outgoing packets.

Tracing LAPB and X.25 on /dev/lapb:

To trace LAPB frames and X.25 packets as they are sent or received by LAPB, enter:

hostname# x25trace -i /dev/lapb 

To trace X.25 packets as they are seen by the X25 driver, type one of the two following commands:

hostname# x25trace -i /dev/x25 x25
hostname# x25trace

Tracing LLC2 and X.25 on /dev/llc2:

hostname# x25trace -i /dev/llc2 

The command above captures all LLC frames, including Unnumbered Information frames used to carry CLNP and ES-IS PDUs. When tracing at the X.25 level on an LLC2 link, MAC addresses are displayed as 0:0:0:0:0:0. Tracing at the LLC2 level on the same link returns the correct MAC addresses.

Tracing a single X.25 connection (logical channel number):

hostname# x25trace -i /dev/lapb x25lcn  lcn_num x25 

Tracing only the next X.25 connection being set up:

hostname# x25trace -i /dev/lapb x25lcn + x25

Tracing LLC2 frames on /dev/llc2:

hostname# x25trace -i /dev/llc2 llc

Tracing X.25 packets to/from specific MAC addresses on /dev/llc2:

hostname# x25trace -i /dev/llc2 srcmac 8:20:0:1:2:3 x25
hostname# x25trace -i /dev/llc2 dstmac 8:20:0:1:2:3 x25
hostname# x25trace -i /dev/llc2 betweenmac 8:20:0:1:2:3 9:0:2b:18:21:5 x25 

Trace outgoing LLC2 frames that are not multicast:

hostname# x25trace -i /dev/llc2 pdu_out not multicast

Redirecting trace of X.25 packets over an LAPB link to a file:

hostname# x25trace -a -i /dev/lapb x25 > /var/adm/x25/packets.record 

Displaying Protocol Statistics

Displaying protocol statistics lets you track what is going on a link or links. You can display statistics on a per-protocol basis, or display statistics for all protocols.

To display statistics, start x25tool, then pull down the Network menu. Choose the Statistics X.25 menu item. The Network Statistics window appears. Choose the protocol you would like statistics for by clicking on the box to the left of the protocol name. You can select more than one protocol; for example, you can select X.25 and MLP.

Once you have select a protocol or protocols, specify a Link Number or All. Specify the Interval (in seconds) that Statistics should be collected for, and the level of detail you require. For example, you may want to isolate the statistics for a particular VC, if you suspect that is where the problem is. Click on Display to display the statistics--Clear resets them to zero. Once you are happy with your settings, click on Apply.

To collect and display statistics, click on the Display button in the Network Statistics window. Statistics appear in the window and are updated every time the Interval elapses. If you do not have x25tool running on your system, you can access the same information by running the command x25stat.

Logging Trace Information

The SunOS 5.x streams strace (1M) command lets you log trace information. See the strace man page for details on the command's use.

The strace command must be followed by three arguments:

module id

Table 11-2 lists the possible values:

link number

The number of the link over which the driver you are tracing is running, or all to specify all links.

level

The tracing level that allows you to receive more or fewer packets or frames. Table 11-3 lists the available strace tracing levels for the X.25, LAPB, and LLC2 drivers.

Specify all to trace all available levels. For example, to trace X.25 PLP packets on all links at all tracing levels, type:

# /usr/sbin/strace 200 all all

Note that strace is owned by root and is executable only by root.

The tracing of an incoming event does not mean that the packet or frame has been accepted by the driver at the layer you are tracing. This is because, for a given layer, the tracing of incoming events is triggered on receiving data from the layer below. At this point, the packet or frame is not yet verified. If the packet or frame is subsequently found to be in error, it might be discarded or cause some further protocol action.

The successful completion of a trace of an outgoing event at the X.25 layer does not necessarily mean that the packet has been sent to the link layer. Following tracing, various consistency checks are performed on the link-level database. If these checks fail, the packet will be discarded. At the LAPB and LLC2 layers, successful tracing does mean that the frame was sent to the WAN or LAN driver. However, it does not mean that the frame will be transmitted on the line.

Capturing Streams Error Messages

In Solstice X.25, the X.25, LAPB, and LLC2 drivers can generate streams error messages. The SunOS 5.x streams strerr (1M) daemon captures streams error messages. This daemon receives error messages and appends them to log files in /var/adm/streams. Log file names take the form error.mm-dd, where mm and dd indicate the month and day the messages were written to the file.

If you are experiencing problems with Solstice X.25 and are uncertain of the source, run strerr. If you receive a streams error message, contact your local Sun customer service representative.

You must be root to run the strerr daemon. Start it like this:

hostname# /usr/sbin/strerr &

The daemon runs until you kill it.

See the strerr man page for a description of the syntax of the messages in the streams error message file.