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Types of Interfaces

Interfaces can be permanent or transient, and are used for networking or services:

Permanent Interfaces

Each routing platform uses multiple permanent interfaces as follows:

The JUNOS software boots the packet forwarding component hardware. When these components are running, the control board uses the internal Ethernet interface to transmit hardware status information to the JUNOS software. Information transmitted includes the internal routing platform temperature, the condition of the fans, whether an FPC has been removed or inserted, and information from the craft interface on the LCD panel. The internal Ethernet interface is configured automatically when the JUNOS software boots.

Each routing platform also has two serial ports, labeled console and auxiliary, for connecting tty-type terminals to the routing platform using standard PC-type tty cables. Although these ports are not network interfaces, they do provide access to the routing platform.

Transient Interfaces

The M-series and T-series routing platforms contain slots for installing FPC boards, and each FPC can accommodate up to four PICs. The PICs provide the actual physical interfaces to the network. The MX-series routing platforms contain slots for installing DPC boards, and the DPC provides the physical interfaces to the network. These physical interfaces are transient interfaces of the routing platform. They are referred to as transient because you can hot-swap a DPC or FPC and its PICs at any time.

You can insert any FPC or DPC into any slot of the appropriate routing platform. You can generally place any combination of PICs in any location on an FPC. (You are limited by the total FPC bandwidth, and by the fact that some PICs physically require two or four of the PIC locations on the FPC.)

You must configure each of the transient interfaces based on the slot in which the FPC is installed, the location in which the PIC is installed, and for some PICs, the port to which you are connecting.

You can configure the interfaces on PICs that are already installed in the routing platform as well as interfaces on PICs that you plan to install later. The JUNOS software detects which interfaces are actually present, so when the software activates its configuration, it activates only present interfaces and retains the configuration information for the interfaces that are not present. When the JUNOS software detects that an FPC containing PICs has been inserted into the routing platform, the software activates the configuration for those interfaces.

Services Interfaces

Services interfaces enable you to incrementally add services to your network. The JUNOS software supports the following services PICs:

Container Interfaces

Container interfaces provide the following features:

Note: Paired groups and true unidirectional APS are not currently supported.

Traditional APS Concept

Traditional APS is configured on two independent physical SONET interfaces: one configured as the working circuit and the other as the protect circuit (see Figure 1). The circuit, named Circuit X in the figure, is the link between the two SONET interfaces.

Figure 1: APS Interface

Image g016918.gif

Traditional APS uses routing protocols that run on each individual SONET interface (since circuit is an abstract construct, instead of being an actual interface). When the working link goes down, the APS infrastructure brings up the protect link and its underlying logical interfaces, and brings down the working link and its underlying logical interfaces, causing the routing protocols to reconverge. This consumes time and leads to traffic loss even though the APS infrastructure has performed the switch quickly.

Container Interfaces Concept

To solve this problem, the JUNOS software provides a soft interface construct called a container interface (see Figure 2).

Figure 2: Container Interface

Image g016919.gif

The container interface allows routing protocols to run on the logical interfaces associated with a virtual container interface instead of on the physical SONET interfaces. When APS switches the underlying physical link based on a fault condition, the container interface remains up, and the logical interface on the container interface does not flap. The routing protocols remain unaware of the APS switching.

APS Support for Container-Based Interfaces

With the container interface, APS is configured on the container interface itself. Individual member SONET links are either marked as primary (corresponding to the working circuit) or standby (corresponding to the protect circuit) in the configuration. No circuit or group name is specified in the container interface model; physical SONET links are put in an APS group by linking them to a single container interface. APS parameters are specified at the container interface level, and are propagated to the individual SONET links by the APS daemon.

Autocopy of APS Parameters

Typical applications require copying APS parameters from the working circuit to the protect circuit, since most of the parameters must be the same for both circuits. This is automatically done in the container interface. APS parameters are specified only once under the container physical interface configuration, and are internally copied over to the individual physical SONET links.

For more information, see Configuring Container Interfaces.

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