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natmip — IP over ATM PVCs
device atm options NATM
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 220.127.116.11 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
Suppose you have 3 hosts 18.104.22.168, 22.214.171.124 and 126.96.36.199 connected by ATM through PVCs: between 188.8.131.52 and 184.108.40.206: 0xc9 UBR between 220.127.116.11 and 18.104.22.168: 0xca VBR between 22.214.171.124 and 126.96.36.199: 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 188.8.131.52: ifconfig en0 184.108.40.206 netmask 0xffffff00 up route add -iface 220.127.116.11 -link en0:3.0.0.c9.0 route add -iface 18.104.22.168 -link en0:3.0.0.ca.3.0.c22.214.171.124.10.0.0.a on host 126.96.36.199: ifconfig en0 188.8.131.52 netmask 0xffffff00 up route add -iface 184.108.40.206 -link en0:3.0.0.c9.0 route add -iface 220.127.116.11 -link en0:3.0.0.cb.1.1.86.a0 on host 18.104.22.168: ifconfig en0 22.214.171.124 netmask 0xffffff00 up route add -iface 126.96.36.199 -link en0:3.0.0.ca.3.0.c188.8.131.52.10.0.0.a route add -iface 184.108.40.206 -link en0:3.0.0.cb.1.1.86.a0 This can also be done in rc.conf(5): on host 220.127.116.11: network_interfaces="lo0 en0" ifconfig_en0="inet 18.104.22.168 netmask 255.255.255.0" static_routes="host2 host3" route_host2="-iface 22.214.171.124 -link en0:3.0.0.c9.0" route_host3="-iface 126.96.36.199 -link en0:3.0.0.ca.3.0.c188.8.131.52.10.0.0.a" on host 184.108.40.206: network_interfaces="lo0 en0" ifconfig_en0="inet 220.127.116.11 netmask 255.255.255.0" static_routes="host1 host3" route_host1="-iface 18.104.22.168 -link en0:3.0.0.c9.0" route_host3="-iface 22.214.171.124 -link en0:3.0.0.cb.1.1.86.a0" on host 126.96.36.199: network_interfaces="lo0 en0" ifconfig_en0="inet 188.8.131.52 netmask 255.255.255.0" static_routes="host1 host2" route_host1="-iface 184.108.40.206 -link en0:3.0.0.ca.3.0.c220.127.116.11.10.0.0.a" route_host2="-iface 18.104.22.168 -link en0:3.0.0.cb.1.1.86.a0"
Chuck Cranor of Washington University implemented the NATM protocol layer along with the EN ATM driver in 1996 for NetBSD.