Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010, Configuration Manual

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Figure 2: NBMA Interface Stack
Unlike standard point-to-point ATM interfaces and broadcast-oriented Ethernet
interfaces, NBMA interfaces form a point-to-multipoint connection. For example,
you can use NBMA to connect a router to multiple stations.
An NBMA interface consists of a single ATM 1483 subinterface that has two or more
VCs. You can add circuits to an existing ATM 1483 subinterface at any time. New
circuits become usable after they have valid ARP table entries. NBMA circuits support
only IP directly over ATM 1483.
The software restricts NBMA interfaces so that all circuits reside on the same physical
interface. An NBMA interface can use as many PVCs as are available on a physical
port.
ARP Table
To maintain the Address Resolution Protocol (ARP) table, you can use either static
mapping via the CLI or Inverse ARP (InARP). InARP provides a way of determining
the IP address of the device at the far end of a circuit. For NBMA interfaces, InARP
enables automatic creation of ARP table entries for each circuit on the interface.
You must enable InARP when you create a PVC by using the atm pvc command.
After you configure InARP, a protocol mapping between an ATM PVC and a network
address is learned dynamically as a result of the exchange of InARP packets.
Static Map Versus Inverse ARP
If the device at the other end of a circuit does not support InARP, static mapping is
required for that circuit. One of these two methods must be used to generate an ARP
table entry for each circuit of the NBMA interface.
InARP and static mapping are complementary within an NBMA subinterface, but are
not compatible with regard to individual circuits. If InARP is configured on a circuit,
the corresponding virtual circuit descriptor (VCD) cannot be present in a static map
applied to that interface.
Aging
ARP table entries, with the exception of those declared static, are aged out based on
an aging interval defined on a subinterface basis. For the purposes of aging, entries
produced via a static map are treated as static ARP table entries. InARP-generated
entries are also treated as static; however, the InARP state machine automatically
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ATM NBMA
JUNOSe 11.1.x Link Layer Configuration Guide