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M10i Routing Engine Description


The Routing Engine runs Junos OS. The software processes that run on the Routing Engine maintain the routing tables, manage the routing protocols used on the router, control the router's interfaces, control some chassis components, and provide the interface for system management and user access to the router.

For a description of the Routing Engine's role in router architecture, see M10i Routing Engine Architecture Overview.


The M10i router supports the Routing Engine 400, Routing Engine 850, and Routing Engine 1800.

One or two Routing Engines can be installed into the midplane from the front of the chassis, as shown in M10i Chassis Description. If two Routing Engines are installed, the High-Availability Chassis Manager (HCM) determines which is the master and which is backup (in standby mode and so performs no functions). By default, the Routing Engine in the slot labeled RE0 is the master. To change the default master Routing Engine, include the appropriate [edit chassis redundancy routing-engine] statement in the configuration, as described in the section about Routing Engine redundancy in the Junos OS Administration Library.


If two Routing Engines are installed, they must both be the same hardware model.

The Routing Engine is hot-pluggable, as described in M10i Field-Replaceable Units (FRUs). If two Routing Engines are installed, removal or failure of the backup Routing Engine does not affect router function. Removal or failure of the master Routing Engine affects forwarding and routing based on the high availability configuration:

  • Dual Routing Engines without any high availability features enabled—Traffic is interrupted while the Packet Forwarding Engine is reinitialized. All kernel and forwarding processes are restarted. When the switchover to the new master Routing Engine is complete, routing convergence takes place and traffic is resumed.

  • Graceful Routing Engine switchover (GRES) is enabled—Graceful Routing Engine switchover preserves interface and kernel information. Traffic is not interrupted. However, graceful Routing Engine switchover does not preserve the control plane. Neighboring routers detect that the router has restarted and react to the event in a manner prescribed by individual routing protocol specifications. To preserve routing without interruption during a switchover, graceful Routing Engine switchover must be combined with nonstop active routing.

  • Nonstop active routing is enabled (graceful Routing Engine switchover must be configured for nonstop active routing to be enabled)—Nonstop active routing supports Routing Engine switchover without alerting peer nodes that a change has occurred. Nonstop active routing uses the same infrastructure as graceful Routing Engine switchover to preserve interface and kernel information. However, nonstop active routing also preserves routing information and protocol sessions by running the routing protocol process (rpd) on both Routing Engines. In addition, nonstop active routing preserves TCP connections maintained in the kernel.

  • Graceful restart is configured—Graceful restart provides extensions to routing protocols so that neighboring helper routers restore routing information to a restarting router. These extensions signal neighboring routers about the graceful restart and prevent the neighbors from reacting to the router restart and from propagating the change in state to the network during the graceful restart period. Neighbors provide the routing information that enables the restarting router to stop and restart routing protocols without causing network reconvergence. Neighbors are required to support graceful restart. The routing protocol process (rpd) restarts. A graceful restart interval is required. For certain protocols, a significant change in the network can cause graceful restart to stop.

If you do not configure graceful Routing Engine switchover, graceful restart, or nonstop active routing, you can configure automatic Routing Engine mastership failover. For information about configuring automatic mastership failover, see the Junos OS Administration Library.


Router performance might change if the backup Routing Engine's configuration differs from the former master's configuration. For the most predictable performance, configure the two Routing Engines identically, except for parameters unique to each Routing Engine.


For information about configuring graceful Routing Engine switchover, graceful restart, and nonstop active routing, see the Junos OS High Availability Library for Routing Devices.


The first supported release for graceful Routing Engine switchover and nonstop active routing on the M10i router is Junos OS Release 6.1 and Junos OS Release 8.4, respectively. However, for graceful Routing Engine switchover we recommend Junos OS Release 7.0 or later. Graceful restart software requirements are dependent on the routing protocols configured on the router. For the minimum software requirements for graceful restart, see the Junos OS High Availability Library for Routing Devices.

For replacement instructions, see Replacing the M10i Routing Engine.