Types of Interfaces

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

• Permanent interfaces—Interfaces that are always present in the router.
• Transient interfaces—Interfaces that can be inserted into or removed from the router depending on your network configuration needs.
• Networking interfaces—Interfaces, such as Ethernet or SONET interfaces, that primarily provide traffic connectivity.
• Services interfaces—Interfaces that provide specific capabilities for manipulating traffic before it is delivered to its destination.

Permanent Interfaces

Each router has two permanent interfaces:

• Management Ethernet interface—Provides an out-of-band method for connecting to the router. You can connect to the management interface over the network using utilities such as ssh and Telnet. SNMP can use the management interface to gather statistics from the router.
• Internal Ethernet interface—Connects the Routing Engine (the portion of the router running the JUNOS Internet software) to the System Control Board (SCB), the System and Switch Board (SSB), the Forwarding Engine Board (FEB), or the System and Forwarding Module (SFM), depending on router model, which is part of the Packet Forwarding Engine. The router uses this interface as the main communications link between the JUNOS software and the components of the Packet Forwarding Engine and runs the embedded microkernel.

The JUNOS software boots the Packet Forwarding Engine hardware, including the control board (SCB, SSB, FEB, or SFM), FPCs, and PICs. 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 router temperature, the condition of the fans, whether an FPC has been removed or inserted, and information from the craft interface on the LCD display panel. The internal Ethernet interface is configured automatically when the JUNOS software boots.

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

Transient Interfaces

The router contains slots for installing FPC boards, and each FPC can accommodate up to four PICs, which provide the actual physical interfaces to the network. These physical interfaces are the router's transient interfaces. They are referred to as transient because you can hot-swap an FPC and its PICs at any time.

You can insert any FPC into any of the router's slots, and you can generally place any combination of PICs in any location on an FPC. (You are limited by the total FPC bandwidth, which cannot exceed the equivalent of an OC-48 link 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 router 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 router, 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:

• ES PIC—Provides a security suite for the IPv4 and IPv6 network layers. The suite provides functionality such as authentication of origin, data integrity, confidentiality, replay protection, and non-repudiation of source. It also defines mechanisms for key generation and exchange, management of security associations, and support for digital certificates.
• Multilink Services and Link Services PICs—Enable you to split, recombine, and sequence datagrams across multiple logical data links. The goal of multilink operation is to coordinate multiple independent links between a fixed pair of systems, providing a virtual link with greater bandwidth than any of the members. The JUNOS software supports two multilink-based services PICs: the Multilink Services PIC and the Link Services PIC.
• Monitoring Services PIC—Enables you to monitor traffic flow and export the monitored traffic. Monitoring traffic allows you to gather and export detailed information about IPv4 traffic flows between source and destination nodes in your network; sample all incoming IPv4 traffic on the monitoring interface and present the data in cflowd record format; perform discard accounting on an incoming traffic flow; encrypt or tunnel outgoing cflowd records, intercepted IPv4 traffic, or both; and direct filtered traffic to different packet analyzers and present the data in its original format.
• Tunnel Services PIC—By encapsulating arbitrary packets inside a transport protocol, tunneling provides a private, secure path through an otherwise public network. Tunnels connect discontinuous subnetworks and enable encryption interfaces, virtual private networks (VPNs), and Multiprotocol Label Switching (MPLS).

For detailed information about configuring services, see the JUNOS Internet Software Configuration Guide: Services Interfaces.