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NAME
natmip — IP over ATM PVCs
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_addr(3)) 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 ⟨remote IP address⟩ -link ⟨iface⟩:⟨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.conf(5):
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"
SEE ALSO
en(4), fatm(4), hatm(4), natm(4), patm(4)
AUTHORS
Chuck Cranor of Washington University implemented the NATM protocol layer along with the EN
ATM driver in 1996 for NetBSD.