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    Broadband Gateway Redundancy Overview

    The MobileNext Broadband Gateway chassis contains Routing Engines, session Dense Port Concentrators (DPCs), and interface DPCs or Modular Port Concentrators (MPCs) (housing PFEs). Whether used as a GPRS gateway support node (GGSN) or Packet Data Network Gateway (P-GW), service and interface cards running the mobility package are configured to provide redundancy similar to that between the Routing Engines. However, different types of redundancy are used for the different levels of hardware used in the broadband gateway.

    The broadband gateway consists of Routing Engines (we recommend two), sessions DPCs (we recommend two or more), and interface PFEs (we recommend two or more DPCs or MPCs). Other service DPCs and interface cards can be installed, but only the elements configured to run the mobility software package can be part of the broadband gateway function. In other words, some elements of the broadband gateway might not be involved in mobile packet flows, but they implement a provider edge (PE) router function, related network address translation (NAT) or IPsec services, and so on. This topic describes only the mobile redundancy portion of the configuration.

    Figure 1 shows that redundancy is available for the Routing Engines, session DPCs, and interface PFEs (housed in interface DPCs or MPCs). However, there are important differences in each type.

    Figure 1: Redundancy Available on the Broadband Gateway

    Redundancy Available on the Broadband
Gateway

    This redundancy configuration overview covers:

    Routing Engine Redundancy

    The Routing Engine is an Intel-based PCI platform that runs the Junos OS software on all product lines. The software processes that run on the Routing Engine oversee all of the functions that perform the mobility tasks running on the chassis. On the MobileNext Broadband Gateway, there is 1:1 redundancy on the Routing Engines when two (the maximum) are installed.

    When two Routing Engines are installed in the broadband gateway, both are powered on, but only one is active (the master). At boot time, both Routing Engines run an arbitration algorithm and elect one as master. The second Routing Engine is in standby mode and performs no functions. If the master Routing Engine fails, the standby unit takes over.

    By default, the master Routing Engine is RE0. You can change the default master by including the appropriate routing-engine statement at the [edit chassis redundancy hierarchy level.

    Note: Although you can run the broadband gateway with only one Routing Engine, we do not recommend it.

    The Routing Engine components are hot-pluggable. Removal or failure of the standby does not affect the function of the broadband gateway.

    However, if the master Routing Engine is removed from the chassis:

    • If there is only one Routing Engine, then packet forwarding halts until the Routing Engine is reinstalled and functioning normally.
    • If there are two Routing Engines, packet forwarding halts while the standby Routing Engine becomes the master.

    You can configure the broadband gateway so that the standby Routing Engine automatically becomes the master if it stops receiving keepalive signals from the original master. You can also configure automatic switchover for other problems on the master, such as a hard disk failure. For more information, see the section about Routing Engine redundancy in the Junos OS System Basics Configuration Guide.

    Session DPC Redundancy

    The MobileNext Broadband Gateway chassis includes a number of session DPCs (we recommend at least two). Each session DPC consists of two services PICs: services PIC 0 (SP0) and services PIC 1 (SP1). The session DPCs anchor control plane functions on the broadband gateway. The anchor DPC can be an individual PIC or aggregate.

    The session DPCs support 1:1 redundancy. That is, the PICs in the session DPCs are configured in a one-to-one correspondence with their backups. So, for example, if the PIC0 in the session DPC in FPC slot 0 is paired with PIC0 in the session DPC in FPC slot 1, one PIC will back up the other PIC. These pairs are called aggregate multiservices (ams-) DPCs. However, the standby device is lost as a services DPC and all services are supplied by the active DPC PIC. In this case, the session DPC PICs associate ams-0/0/0 and ams-1/0/0. You also configure units for AMS interfaces, and these are used for AAA and charging.

    Note: You cannot configure a services PIC logical interface (ms-0/0/0.0, for example) if you also make the same logical interface part of an AMS group (ams-0/0/0.0 for example). This configuration will not commit.

    You configure the AMS member interface that is the preferred backup.

    Interface Redundancy

    The MobileNext Broadband Gateway chassis includes a number of interface Packet Forwarding Engines housed on DPCs or MPCs (we recommend at least two DPCs or MPCs). Each Packet Forwarding Engine consists of two or four Packet Forwarding Engines, depending on the DPC or MPC type. These are PFE0 and PFE1 (or optionally, PFE2 and PFE3). Some Packet Forwarding Engines are designated as anchor devices, and keep various parameters for the data plane traffic flow. Packets related to a particular flow must be processed by an anchor Packet Forwarding Engine. The anchor Packet Forwarding Engine can be a single Packet Forwarding Engine or an aggregate.

    The interface Packet Forwarding Engines offer N:1 redundancy. That is, a configured number of interface Packet Forwarding Engines (N) are backed up by one warm standby Packet Forwarding Engine. Optionally, you can group Packet Forwarding Engines for redundancy purposes so that each member of the group shares the same fate.

    To configure redundancy, you select a list of interface Packet Forwarding Engines to place on the active (primary) list. Then you select a different Packet Forwarding Engine to act as the secondary (standby) Packet Forwarding Engine for all Packet Forwarding Engines in the active group.

    Published: 2011-11-22