ifconfig and lmcconfig

The program lmcconfig(8) manipulates interface parameters beyond the scope of ifconfig(8). lmcconfig has many flags and options, but in normal operation only a few are needed.

lmcconfig lmc0

displays interface configuration and status.

lmcconfig lmc0 -X 1

selects the built-in RawIP line protocol stack.

lmcconfig lmc0 -X 2 -x 2

selects the SPPP stack and the PPP protocol.

Some configuration options are available through ifconfig as well as lmcconfig.

ifconfig -m lmc0

lists the available media options.

ifconfig lmc0 mediaopt loopback

loops the interface transmitter to the receiver for testing. This loopback uses a path present in every card type. lmcconfig can select card-specific loopbacks, such as outbound payload loopback.

ifconfig lmc0 debug

enables debugging output from the device driver and from the line protocol stack above it.

lmcconfig lmc0 -D

enables debugging output from the device driver.

Debugging messages that appear on the console are also written to file /var/log/messages. Caution: when things go very wrong, a torrent of debugging messages can swamp the console and bring a machine to its knees.

Operation

Configure a PPP link using SPPP with

lmcconfig lmc0 -X 2 -x 2 
ifconfig lmc0 10.0.0.1 10.0.0.2

Configure a Cisco-HDLC link using SPPP with

lmcconfig lmc0 -X 2 -x 3 
ifconfig lmc0 10.0.0.1 10.0.0.2

Configure a RAWIP link with

lmcconfig lmc0 -X 1 
ifconfig lmc0 10.0.0.1 10.0.0.2

Testing with Loopbacks

Testing with loopbacks requires only one card and can test everything on that card. Packets can be looped back at many points: in the PCI chip, in the modem chips, through a loopback plug, in the local external equipment, or at the far end of a circuit.

All cards can be looped through the PCI chip. Cards with internal modems can be looped through the modem framer and the modem line interface. Cards for external modems can be looped through the driver/receiver chips. See lmcconfig(8) for details.

Configure the card with

ifconfig lmc0 10.0.0.1 10.0.0.1

HSSI

Loopback plugs can be ordered from SBE (and others). Transmit clock is normally supplied by the external modem. When an HSSI card is operated with a loopback plug, the PCI bus clock must be used as the transmit clock, typically 33 MHz. When testing an HSSI card with a loopback plug, configure it with

lmcconfig lmc0 -a 2

“-a 2” selects the PCI bus clock as the transmit clock.

T3

Connect the two BNC jacks with a short coax cable.

SSI

Loopback plugs can be ordered from SBE (only). Transmit clock is normally supplied by the external modem. When an SSI card is operated with a loopback plug, the on-board clock synthesizer must be used. When testing an SSI card with a loopback plug, configure it with

lmcconfig lmc0 -E -f 10000000

“-E” puts the card in DCE mode to source a transmit clock. “-f 10000000” sets the internal clock source to 10 Mb/s.

T1/E1

A loopback plug is a modular plug with two wires connecting pin 1 to pin 4 and pin 2 to pin 5.

One can also test by connecting to a local modem (HSSI and SSI) or NI (T1 and T3) configured to loop back. Cards can generate signals to loopback remote equipment so that complete circuits can be tested; see lmcconfig(8) for details.

Testing with a Modem

Testing with a modem requires two cards of different types. The cards can be in the same machine or different machines.

Configure the two cards with

ifconfig lmc0 10.0.0.1 10.0.0.2 
ifconfig lmc1 10.0.0.2 10.0.0.1

T3/HSSI

If you have a T3 modem with an HSSI interface (made by Digital Link, Larscom, Kentrox etc.) then use an HSSI card and a T3 card. The coax cables between the card and the modem must “cross over” (see below).

T1/V.35

If you have a T1 (or E1) modem with a V.35, X.21 or EIA530 interface, then use an SSI card and a T1 card. Use a T1 null modem cable (see below) between the external modem and the T1 card.

Testing with a Null Modem Cable

Testing with a null modem cable requires two cards of the same type. The cards can be in the same machine or different machines.

Configure the two cards with

ifconfig lmc0 10.0.0.1 10.0.0.2 
ifconfig lmc1 10.0.0.2 10.0.0.1

HSSI

Three-meter HSSI null-modem cables can be ordered from SBE. In a pinch, a 50-pin SCSI-II cable up to a few meters will work as a straight HSSI cable (not a null modem cable). Longer cables should be purpose-built HSSI cables because the cable impedance is different. Transmit clock is normally supplied by the external modem. When an HSSI card is connected by a null modem cable, the PCI bus clock can be used as the transmit clock, typically 33 MHz. When testing an HSSI card with a null modem cable, configure it with

lmcconfig lmc0 -a 2

“-a 2” selects the PCI bus clock as the transmit clock.

T3

T3 null modem cables are just 75-ohm coax cables with BNC connectors. TX OUT on one card should be connected to RX IN on the other card. In a pinch, 50-ohm thin Ethernet cables usually work up to a few meters, but they will not work for longer runs—75-ohm coax is required.

SSI

Three-meter SSI null modem cables can be ordered from SBE. An SSI null modem cable reports a cable type of V.36/EIA449. Transmit clock is normally supplied by the external modem. When an SSI card is connected by a null modem cable, an on-board clock synthesizer is used. When testing an SSI card with a null modem cable, configure it with

lmcconfig lmc0 -E -f 10000000

“-E” puts the card in DCE mode to source a transmit clock. “-f 10000000” sets the internal clock source to 10 Mb/s.

T1/E1

A T1 null modem cable has two twisted pairs that connect pins 1 and 2 on one plug to pins 4 and 5 on the other plug. Looking into the cable entry hole of a plug, with the locking tab oriented down, pin 1 is on the left. A twisted pair Ethernet cable makes an excellent straight T1 cable. Alas, Ethernet cross-over cables do not work as T1 null modem cables.

LEDs

HSSI and SSI cards should be operational if all three green LEDs are on (the upper-left one should be blinking) and the red LED is off.

RED	upper-right	No Transmit clock
GREEN	upper-left	Device driver is alive if blinking
GREEN	lower-right	Modem signals are good
GREEN	lower-left	Cable is plugged in (SSI only)

T1/E1 and T3 cards should be operational if the upper-left green LED is blinking and all other LEDs are off. For the T3 card, if other LEDs are on or blinking, try swapping the coax cables!

RED	upper-right	Received signal is wrong
GREEN	upper-left	Device driver is alive if blinking
BLUE	lower-right	Alarm Information Signal (AIS)
YELLOW	lower-left	Remote Alarm Indication (RAI)

RED	blinks if an outward loopback is active.
GREEN	blinks if the device driver is alive.
BLUE	blinks if sending AIS, on solid if receiving AIS.
YELLOW	blinks if sending RAI, on solid if receiving RAI.

Packet Lengths

Maximum transmit and receive packet length is unlimited. 
Minimum transmit and receive packet length is one byte.

Cleaning up after one packet and setting up for the next packet involves making several DMA references. This can take longer than the duration of a short packet, causing the adapter to fall behind. For typical PCI bus traffic levels and memory system latencies, back-to-back packets longer than about 20 bytes will always work (53 byte cells work), but a burst of several hundred back-to-back packets shorter than 20 bytes will cause packets to be dropped. This usually is not a problem since an IPv4 packet header is at least 20 bytes long.

The device driver imposes no constraints on packet size. Most operating systems set the default Maximum Transmission Unit (MTU) to 1500 bytes; the legal range is usually (72..65535). This can be changed with

ifconfig lmc0 mtu 2000

SPPP enforces an MTU of 1500 bytes for PPP and Cisco-HDLC. RAWIP sets the default MTU to 4032 bytes, but allows it to be changed to anything.

ALTQ: Alternate Output Queue Disciplines

The driver has hooks for altq(9), the Alternate Queueing package. To see ALTQ in action, use your favorite traffic generation program to generate three flows sending down one T3 circuit. Without ALTQ, the speeds of the three connections will vary chaotically. Enable ALTQ and two of the connections will run at about 20 Mb/s and the third will run at about 2 Mb/s.

Enable altqd(8) and add the following lines to /etc/altq.conf:

interface lmc0 bandwidth 44M hfsc 
class hfsc lmc0 a root pshare 48 
filter lmc0 a 10.0.0.2 12345 10.0.0.1 0 6 
filter lmc0 a 10.0.0.1 0 10.0.0.2 12345 6 
class hfsc lmc0 b root pshare 48 
filter lmc0 b 10.0.0.2 12346 10.0.0.1 0 6 
filter lmc0 b 10.0.0.1 0 10.0.0.2 12346 6 
class hfsc lmc0 c root pshare 4 default 
filter lmc0 c 10.0.0.2 12347 10.0.0.1 0 6 
filter lmc0 c 10.0.0.1 0 10.0.0.2 12347 6

The example above requires the altq(4) Hierarchical Fair Service Curve queue discipline to be configured in conf/YOURKERNEL:

options ALTQ 
options ALTQ_HFSC.

BPF: Berkeley Packet Filter

The driver has hooks for bpf(4), the Berkeley Packet Filter, a protocol-independent raw interface to data link layers.

To test the BPF kernel interface, bring up a link between two machines, then run ping(8) and tcpdump(8):

ping 10.0.0.1

and in a different window:

tcpdump -i lmc0

The output from tcpdump should look like this:

03:54:35.979965 10.0.0.2 > 10.0.0.1: icmp: echo request 
03:54:35.981423 10.0.0.1 > 10.0.0.2: icmp: echo reply

Line protocol control packets may appear among the ping packets occasionally.

The kernel must be configured with

options bpfilter

SNMP: Simple Network Management Protocol

The driver is aware of what is required to be a Network Interface Object managed by an Agent of the Simple Network Management Protocol. The driver exports SNMP-formatted configuration and status information sufficient for an SNMP Agent to create MIBs for:

RFC-2233

Interfaces group

RFC-2496

DS3 interfaces

RFC-2495

DS1/E1 interfaces

RFC-1659

RS232-like interfaces

An SNMP Agent is a user program, not a kernel function. Agents can retrieve configuration and status information by using ioctl(2) system calls. User programs should poll sc->cfg.ticks which increments once per second after the SNMP state has been updated.

E1 Framing

Phone companies usually insist that customers put a Frame Alignment Signal (FAS) in time slot 0. A Cyclic Redundancy Checksum (CRC) can also ride in time slot 0. Channel Associated Signalling (CAS) uses Time Slot 16. In telco-speak signalling is on/off hook, ringing, busy, etc. Signalling is not needed here and consumes 64 Kb/s. Only use E1-CAS formats if the other end insists on it! Use E1-FAS+CRC framing format on a public circuit. Depending on the equipment installed in a private circuit, it may be possible to use all 32 time slots for data (E1-NONE).

T3 Framing

M13 is a technique for multiplexing 28 T1s into a T3. Muxes use the C-bits for speed-matching the tributaries. Muxing is not needed here and usurps the FEBE and FEAC bits. Only use T3-M13 format if the other end insists on it! Use T3-CParity framing format if possible. Loop Timing, Fractional T3, and HDLC packets in the Facility Data Link are not supported.

T1 & T3 Frame Overhead Functions

Performance Report Messages (PRMs) are enabled in T1-ESF. 
Bit Oriented Protocol (BOP) messages are enabled in T1-ESF. 
In-band loopback control (framed or not) is enabled in T1-SF. 
Far End Alarm and Control (FEAC) msgs are enabled in T3-CPar. 
Far End Block Error (FEBE) reports are enabled in T3-CPar. 
Remote Alarm Indication (RAI) is enabled in T3-Any. 
Loopbacks initiated remotely time out after 300 seconds.

T1/E1 'Fractional' 64 kb/s Time Slots

T1 uses time slots 24..1; E1 uses time slots 31..0. E1 uses TS0 for FAS overhead and TS16 for CAS overhead. E1-NONE has no overhead, so all 32 TSs are available for data. Enable/disable time slots by setting 32 1s/0s in a config param. Enabling an E1 overhead time slot, or enabling TS0 or TS25-TS31 for T1, is ignored by the driver, which knows better. The default TS param, 0xFFFFFFFF, enables the maximum number of time slots for whatever frame format is selected. 56 Kb/s time slots are not supported.