SYNOPSIS

device atm options NATM

DESCRIPTION

The NATM protocol stack includes support for IP over ATM. Without any additional signalling stacks or other modules it is possible to build a CLIP (classical IP over ATM) network based on PVCs.

An ATM network card ( en0 in this example) is configured for IP by something like:

"ifconfig en0 128.252.200.1 netmask 0xffffff00 up"

IP routing is done with special interface routes (routes with directly reachable destinations) with a link layer gateway address. The link layer address specifies the ATM interface through which the destination can be reached, the virtual channel that connects to the destination and the ATM characteristics of this channel. The address part of the link layer address (see link_addr3) consists of a fixed part (the first 5 bytes) and a part that depends on the kind of the PVC (UBR, CBR, VBR, ABR). Multi-byte values are big-endian encoded: the bytes with the lower numbers contain the higher order bits.

byte 0

Is a flag byte. Currently only flag 0x20 is used. When set, all IP frames are LLC/SNAP encapsulated before putting them into an AAL5 frame. Setting this flag is recommended and allows interoperability with other CLIP implementations. Note that BPF works only with LLC/SNAP encapsulation.

byte 1

This is the VPI of the channel.

bytes 2...3

VCI of the channel. Must not be zero.

byte 4

Traffic type. One of 0 (UBR), 1 (CBR), 2 (ABR), 3 (VBR).

The variable part for UBR connections may be either empty or three bytes:

bytes 5...7

Specifies the peak cell rate for UBR.

The variable part for CBR connections must be three bytes:

bytes 5...7

Specifies the peak cell rate for CBR.

The variable part for VBR connections must be 9 bytes long and specifies three values:

bytes 5...7

Specifies the peak cell rate for VBR.

bytes 8...10

This is the sustainable cell rate.

bytes 11...13

The maximum burst size.

The variable part for ABR connections must be 19 bytes long and specifies the following values:

bytes 5...7

Specifies the peak cell rate for ABR.

bytes 8...10

The minimum cell rate.

bytes 11...13

The initial cell rate.

bytes 14...16

The transient buffer exposure.

byte 17

The NRM value.

byte 18

The TRM value.

bytes 19...20

The ADTF value.

byte 21

The rate increase factor (RIF).

byte 22

The rate decrease factor (RDF).

byte 23

The cutoff decrease factor (CDF).

To add a PVC the route(8) utility can be used:

route add -iface Aq remote IP address -link Ao iface Ac : Aq lladdr

The iface is the ATM interface through which remote IP address can be reached and lladdr is the link layer address as a string of dot-separated, hexadecimal bytes.

NATM also supports the old, original format. This consists of 4 byte link layer addresses (and the channels are implicit UBR):

byte 0

Flags:

0x01

use AAL5.

0x02

if using AAL5, use an LLC/SNAP header.

Thus, parameter 3 means AAL5 and LLC/SNAP encapsulation (this is the required setting for interworking with other CLIP clients). Note that BPF works only with LLC/SNAP encapsulation.

byte 1

VPI for the channel

bytes 2...3

VCI for the channel

EXAMPLES

Suppose you have 3 hosts 128.252.200.1, 128.252.200.2 and 128.252.200.3 connected by ATM through PVCs:

between 128.252.200.1 and 128.252.200.2: 0xc9 UBR

between 128.252.200.1 and 128.252.200.3: 0xca VBR

between 128.252.200.2 and 128.252.200.3: 0xcb CBR

The parameters for the VBR channel are: PCR 50000, SCR 10000, MBS 10. The peak cell rate for the CBR channel is 100000.

To enable the links use the following commands:

on host 128.252.200.1:

ifconfig en0 128.252.200.1 netmask 0xffffff00 up
route add -iface 128.252.200.2 -link en0:3.0.0.c9.0
route add -iface 128.252.200.3 -link en0:3.0.0.ca.3.0.c3.50.0.27.10.0.0.a

on host 128.252.200.2:

ifconfig en0 128.252.200.2 netmask 0xffffff00 up
route add -iface 128.252.200.1 -link en0:3.0.0.c9.0
route add -iface 128.252.200.3 -link en0:3.0.0.cb.1.1.86.a0

on host 128.252.200.3:

ifconfig en0 128.252.200.3 netmask 0xffffff00 up
route add -iface 128.252.200.1 -link en0:3.0.0.ca.3.0.c3.50.0.27.10.0.0.a
route add -iface 128.252.200.2 -link en0:3.0.0.cb.1.1.86.a0

This can also be done in rc.conf5:

on host 128.252.200.1:

network_interfaces="lo0 en0"
ifconfig_en0="inet 128.252.200.1 netmask 255.255.255.0"
static_routes="host2 host3"
route_host2="-iface 128.252.200.2 -link en0:3.0.0.c9.0"
route_host3="-iface 128.252.200.3 -link en0:3.0.0.ca.3.0.c3.50.0.27.10.0.0.a"

on host 128.252.200.2:

network_interfaces="lo0 en0"
ifconfig_en0="inet 128.252.200.2 netmask 255.255.255.0"
static_routes="host1 host3"
route_host1="-iface 128.252.200.1 -link en0:3.0.0.c9.0"
route_host3="-iface 128.252.200.3 -link en0:3.0.0.cb.1.1.86.a0"

on host 128.252.200.3:

network_interfaces="lo0 en0"
ifconfig_en0="inet 128.252.200.3 netmask 255.255.255.0"
static_routes="host1 host2"
route_host1="-iface 128.252.200.1 -link en0:3.0.0.ca.3.0.c3.50.0.27.10.0.0.a"
route_host2="-iface 128.252.200.2 -link en0:3.0.0.cb.1.1.86.a0"

AUTHORS

An Chuck Cranor of Washington University implemented the NATM protocol layer along with the EN ATM driver in 1996 for Nx .