Configuring an ATM Interface

Problem

You need to get the ATM interface in your router up and running.

Solution

Set up the ATM interface with one virtual path identifier (VPI) and one virtual circuit identifier ( VCI):

	[edit interfaces at-1/0/0 ]
	aviva@M10i#  
set atm-options pic-type atm2 
	aviva@M10i# set atm-options 
vpi 0 
	aviva@M10i# set unit 0 vci 0.32 
	aviva@M10i# set unit 0 family inet address 136.1.1.1/24 

 

Discussion

ATM connections are set up over virtual paths and virtual circuits. The virtual path, represented by a VPI, establishes a route between two devices in a network. Each VPI can contain multiple virtual circuits, each with a VCI. There can be a maximum of 4,090 VCIs, starting at number 32. (Numbers 0 through 31 are reserved.) The VPI can range from 0 through 255. VPIs and VCIs are local to the router, so only the two devices connected by them need know the details of the connection.

This recipe sets up a basic ATM interface for a one-port ATM2 OC-12 PIC that is in slot 1. The ATM interface has a VPI of 0 and a VCI of 32. You configure the virtual circuit on the logical interface because, as the name implies, it's a virtual, not a physical, interface. It is also important to include the set atm-options command to explicitly configure the PIC as an ATM2 PIC type, not an ATM1. Some statements for configuring ATM PICs work either with the ATM1 PIC or the ATM2 PIC, but not both. If you do not use the set atm-options command, and if you use an ATM1-only statement with an ATM2 interface, the JUNOS software assumes that the PIC is an ATM1 and configures it accordingly, but the interface will not operate as you expect it to. The same thing happens if you use ATM2-only statements with an ATM1 interface. In either case, the JUNOS CLI provides no warning or commit error. If, however, you use the set atm-options command and include statements for the other type of ATM PIC, the configuration won't commit and JUNOS CLI error messages will tell you where the problem is.

This recipe is for the newer ATM2 PICs. The configuration for ATM1 PICs is more involved.

Use the show chassis hardware command to check the ATM PIC type:

	aviva@M10i> show chassis hardware
	Hardware inventory:
	Item Version Part number Serial number Description
	Chassis 19155 M10i
	…
	FPC 1 E-FPC
	 PIC 0 REV 02 750-005718 BG0216 1x OC-12 ATM-II IQ, MM
	 PIC 1 REV 09 750-008425 HX1881 Adaptive Services
	 PIC 2 REV 02 750-003748 HC2155 2x OC-3 SONET, SMIR
	 PIC 3 REV 05 750-005726 CC3987 1x OC-12 ATM-II IQ, MM

Use the show interfaces command to check that the ATM interface is correctly configured and is running:

	aviva@M10i> show interfaces at-1/0/0
	Physical interface: at-1/0/0, Enabled, Physical link is Up
	 Interface index: 132, SNMP ifIndex: 49
	 Link-level type: ATM-PVC, MTU: 4482, Clocking: Internal, SONET mode,
	 Speed: OC12, Loopback: None, Payload scrambler: Enabled
	 Device flags : Present Running
	 Link flags : None
	 CoS queues : 4 supported
	 Current address: 00:05:85:70:a4:7e
	 Last flapped : 2005-05-24 17:46:05 PDT (1d 05:11 ago)
	 Input rate : 0 bps (0 pps)
	 Output rate : 0 bps (0 pps)
	 SONET alarms : None
	 SONET defects : None
	 
VPI 0
	 Flags: Active
	 Total down time: 0 sec, Last down: Never
	 Traffic statistics:
	 Input packets: 8918
	 Output packets: 8999

	 Logical interface at-1/0/0.0 (Index 66) (SNMP ifIndex 30)
	 Flags: Point-To-Point SNMP-Traps 16384 Encapsulation: ATM-SNAP
	 Input packets : 8918
	 Output packets: 8999
	 Protocol inet, MTU: 4470
	 Flags: None
	 Addresses, Flags: Is-Preferred Is-Primary
	 Destination: 136.1.1/24, Local: 136.1.1.1, Broadcast: 136.1.1.255
	  
VCI 0.32
	 Flags: Active, 1024
	 Total down time: 0 sec, Last down: Never
	 EPD threshold: 4259, Transmit weight cells: 0
	 Input packets : 8918
	 Output packets: 8999

	 Logical interface at-1/0/0.32767 (Index 67) (SNMP ifIndex 29)
	 Flags: Point-To-Multipoint No-Multicast SNMP-Traps 16384
	 Encapsulation: 
ATM-VCMUX
	 Input packets : 0
	 Output packets: 0
	 
VCI 0.4
	 Flags: Active, 1024
	 Total down time: 0 sec, Last down: Never
	 EPD threshold: 0, Transmit weight cells: 0
	 Input packets : 0
	 Output packets: 0

For the physical interface, the device flags Present, Running indicate that the physical ATM interface is operating properly. For the logical interface, the lack of a Down flag indicates that the logical portion of the interface is up. The Active flag under the VCI shows that the VCI is working.

The configuration of a basic ATM interface is straightforward, and the show interfaces command output illustrates some of the default ATM interface settings. The link-level type is ATM-PVC, the default for interfaces with permanent virtual circuits. The default SONET media MTU for M10i routers is 4,482 bytes, and the default IPv4 MTU size (displayed in the logical interfaces section) is 4,470 bytes. SONET interfaces use the router's internal stratum 3 clock as the default source of the transmit clock. Payload scrambling is also enabled by default to improve link stability.