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Special Interfaces

In addition to the configured network interfaces associated with the physical ports and wires that make up much of the network, J-series Services Routers have special interfaces. Table 27 lists each special interface and briefly describes its use.

For information about interface names, see Network Interface Naming.

Table 27: Special Interfaces on a Services Router

Interface Name

Description

dsc

Discard interface. See Discard Interface.

fxp0

This interface is not supported on a J-series Services Router. (On an M-series or T-series router, fxp0 is used for out-of-band management.) For more information about the J-series Services Router management port interface, see Management Interface.

For information about the interfaces supported on J-series, M-series, and T-series routers, see the JUNOS Interfaces Command Reference.

gr-0/0/0

Configurable generic routing encapsulation (GRE) interface. GRE allows the encapsulation of one routing protocol over another routing protocol.

Within a Services Router, packets are routed to this internal interface, where they are first encapsulated with a GRE packet and then re-encapsulated with another protocol packet to complete the GRE. The GRE interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to perform GRE.

gre

Internally generated GRE interface. This interface is generated by the JUNOS software to handle GRE. It is not a configurable interface.

ip-0/0/0

Configurable IP-over-IP encapsulation (also called IP tunneling) interface. IP tunneling allows the encapsulation of one IP packet over another IP packet.

Generally, IP routing allows packets to be routed directly to a particular address. However, in some instances you might need to route an IP packet to one address and then encapsulate it for forwarding to a different address. In a mobile environment in which the location of the end device changes, a different IP address might be used as the end device migrates between networks.

Within a Services Router, packets are routed to this internal interface where they are encapsulated with an IP packet and then forwarded to the encapsulating packet's destination address. The IP-IP interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to perform IP tunneling.

ipip

Internally generated IP-over-IP interface. This interface is generated by the JUNOS software to handle IP-over-IP encapsulation. It is not a configurable interface.

lo0

Loopback address. The loopback address has several uses, depending on the particular JUNOS feature being configured. See Loopback Interface.

lo0.16385

Internal loopback address. The internal loopback address is a particular instance of the loopback address with the logical unit number 16385. It is created by the JUNOS software as the loopback interface for the internal routing instance. This interface prevents any filter on lo0.0 from disrupting internal traffic.

ls-0/0/0

Configurable link services interface. Link services include the multilink services MLPPP, MLFR, and Compressed Real-Time Transport Protocol (CRTP).

Within a Services Router, packets are routed to this internal interface for link bundling or compression. The link services interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to perform multilink services.

For more information about multilink services, see Services Interfaces.

lsi

Internally generated link services interface. This interface is generated by the JUNOS software to handle multilink services like MLPPP, MLFR, and CRTP. It is not a configurable interface.

lt-0/0/0

Interface used to provide class-of-service (CoS) support for data link switching (DLSw) traffic and real-time performance monitoring (RPM) probe packets.

Within a Services Router, packets are routed to this internal interface for services. The lt interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to perform CoS for DLSW and RPM services.

Note: The lt interface on the M-series and T-series routing platforms supports configuration of logical routers—the capability to partition a single physical router into multiple logical devices that perform independent routing tasks. However, the lt interface on the J-series Services Router does not support logical routers.

mt-0/0/0

Configurable multicast tunnel interface. Multicast tunnels filter all unicast packets; if an incoming packet is not destined for a 224/8-or-greater prefix, the packet is dropped and a counter is incremented.

Within a Services Router, packets are routed to this internal interface for multicast filtering. The multicast tunnel interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to perform multicast tunneling.

mtun

Internally generated multicast tunnel interface. This interface is generated by the JUNOS software to handle multicast tunnel services. It is not a configurable interface.

pd-0/0/0

Configurable Protocol Independent Multicast (PIM) de-encapsulation interface. In PIM sparse mode, the first-hop routing platform encapsulates packets destined for the rendezvous point router. The packets are encapsulated with a unicast header and are forwarded through a unicast tunnel to the rendezvous point. The rendezvous point then de-encapsulates the packets and transmits them through its multicast tree.

Within a Services Router, packets are routed to this internal interface for de-encapsulation. The PIM de-encapsulation interface is an internal interface only and is not associated with a physical medium or Physical Interface Module (PIM). You must configure the interface for it to perform PIM de-encapsulation.

pe-0/0/0

Configurable Protocol Independent Multicast (PIM) encapsulation interface. In PIM sparse mode, the first-hop routing platform encapsulates packets destined for the rendezvous point router. The packets are encapsulated with a unicast header and are forwarded through a unicast tunnel to the rendezvous point. The rendezvous point then de-encapsulates the packets and transmits them through its multicast tree.

Within a Services Router, packets are routed to this internal interface for encapsulation. The PIM encapsulation interface is an internal interface only and is not associated with a physical medium or Physical Interface Module (PIM). You must configure the interface for it to perform PIM encapsulation.

pimd

Internally generated Protocol Independent Multicast (PIM) de-encapsulation interface. This interface is generated by the JUNOS software to handle PIM de-encapsulation. It is not a configurable interface.

pime

Internally generated Protocol Independent Multicast (PIM) encapsulation interface. This interface is generated by the JUNOS software to handle PIM encapsulation. It is not a configurable interface.

pp0

Configurable PPPoE encapsulation interface. PPP packets being routed in an Ethernet network use PPPoE encapsulation.

Within a Services Router, packets are routed to this internal interface for PPPoE encapsulation. The PPPoE encapsulation interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to forward PPPoE traffic. For more information about PPPoE interfaces, see Configuring Point-to-Point Protocol over Ethernet.

sp-0/0/0

Configurable services interface. The services interface is used to enable a number of routing services such as stateful firewall filters, IPSec, and Network Address Translation (NAT).

Within a Services Router, packets are routed to this internal interface for encapsulation or processing, depending on the services configured. The configurable services interface is an internal interface only and is not associated with a physical medium or PIM. You must configure the interface for it to enable service sets.

tap

Internally generated interface. This interface is generated by the JUNOS software to monitor and record traffic during passive monitoring. When packets are discarded by the Packet Forwarding Engine, they are placed on this interface. It is not a configurable interface.

umd0

Configurable USB modem physical interface. This interface is detected when a USB modem is connected to the USB port on the Services Router.

Note: The J4350 and J6350 Services Routers have two USB ports. However, you can connect only one USB modem to the USB ports on these routers. If you connect USB modems to both the USB ports, only the first USB modem connected to the router is recognized.

Discard Interface

The discard (dsc) interface is not a physical interface, but a virtual interface that discards packets. You can configure one discard interface. This interface allows you to identify the ingress (inbound) point of a denial-of-service (DoS) attack. When your network is under attack, the target host IP address is identified, and the local policy forwards attacking packets to the discard interface. Traffic routed out the discard interface is silently discarded.

Loopback Interface

The Internet Protocol (IP) specifies a loopback network with the (IPv4) address 127.0.0.0/8. Most IP implementations support a loopback interface (lo0) to represent the loopback facility. Any traffic that a computer program sends on the loopback network is addressed to the same computer. The most commonly used IP address on the loopback network is 127.0.0.1 for IPv4 and ::1 for IPv6. The standard domain name for the address is localhost.

The loopback interface can perform the following functions:

Management Interface

The management interfaces (also called the out-of-band management interfaces) on a J-series Services Router are located on the front panel of the router chassis. The number and type of management interfaces depend on the model of the Services Router as follows:

The management interfaces are the primary interfaces for accessing the router remotely. Typically, a management interface is not connected to the in-band network, but is connected instead to the router's internal network. Through a management interface you can access the router over the network and configure it from anywhere, regardless of its physical location.

As a security feature, users cannot log in as root through a management interface. To access the router as root, you must use the console port.

Services Interfaces

On Juniper Networks M-series and T-series routing platforms, individual services such as IP-over-IP encapsulation, link services such as multilink protocols, adaptive services such as stateful firewall filters and NAT, and sampling and logging capabilities are implemented by services Physical Interface Cards (PICs). On a J-series Services Router, these same features are implemented by the general-purpose CPU on the main circuit board.

Although the same JUNOS software image supports the services features across all routing platforms, on a Services Router no Physical Interface Module (PIM) is associated with services features.

To configure services on a Services Router, you must configure one or more internal interfaces by specifying PIM slot 0 and port 0—for example, sp-0/0/0 for stateful firewall filters and NAT or gr-0/0/0 for GRE.

Services Routers support multilink protocol services on the ls-0/0/0 interface. At the logical level, the ls-0/0/0 interface supports the Multilink Point-to-Point Protocol (MLPPP) and Multilink Frame Relay (MLFR) FRF.15 encapsulation types, and at the physical level, the interface supports the MLRF FRF.16 encapsulation type and Compressed Real-Time Transport Protocol (CRTP).

MLPPP and MLFR

Multilink Point-to-Point Protocol (MLPPP) is a protocol for aggregating multiple constituent links into one larger PPP bundle. Multilink Frame Relay (MLFR) allows you to aggregate multiple Frame Relay links by inverse multiplexing. MLPPP and MLFR provide service options between low-speed T1 and E1 services. In addition to providing additional bandwidth, bundling multiple links can add a level of fault tolerance to your dedicated access service. Because you can implement bundling across multiple interfaces, you can protect users against loss of access when a single interface fails.

MLFR Frame Relay Forum

JUNOS supports FRF.12 fragmentation header formats for both FRF.15 (MLFR) and FRF.16 (MFR).

MLFR Frame Relay Forum 15 (FRF.15) combines multiple permanent virtual circuits (PVCs) into one aggregated virtual circuit (AVC). This process provides fragmentation over multiple PVCs on one end and reassembly of the AVC on the other end. MLFR FRF.15 is supported on the ls-0/0/0 interface.

MLFR FRF.16 is supported on the ls-0/0/0:channel, which carries a single MLFR FRF.16 bundle. MLFR FRF.16 combines multiple links to form one logical link. Packet fragmentation and reassembly occur on each virtual circuit. Each bundle can support multiple virtual circuits.

Note: If you configure a permanent virtual circuit (PVC) between T1, E1, T3, or E3 interfaces in J-series router and another vendor, and the other vendor does not have the same FRF.12 support or supports FRF.12 in a different way, the J–series interface might discard a fragmented packet containing FRF.12 headers and count it as a "Policed Discard." Therefore, when you configure a PVC between T1, E1, T3, or E3 interfaces in J-series router and another vendor, you should configure multilink bundles on both peers and configure fragmentation thresholds on the multilink bundle.

CRTP

Real-Time Transport Protocol (RTP) can help achieve interoperability among different implementations of network audio and video applications. However, the header can be too large a payload for networks using low-speed lines such as dial-up modems. Compressed Real-Time Transport Protocol (CRTP) can reduce network overhead on a low-speed link. On a Services Router, CRTP can operate on a T1 or E1 interface with PPP encapsulation.

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