Nonstop Active Routing System Requirements

This section contains the following topics:

• Nonstop Active Routing Platform Support
• Nonstop Active Routing Protocol and Feature Support
• Nonstop Active Routing BFD Support
• Nonstop Active Routing BGP Support
• Nonstop Active Routing Layer 2 Circuit and LDP-Based VPLS Support
• Nonstop Active Routing PIM Support
• Nonstop Active Routing Support for RSVP-TE LSPs

Nonstop Active Routing Platform Support

Table 8 lists the platforms that support nonstop active routing.

Table 8: Nonstop Active Routing Platform Support

Note: All Routing Engines configured for nonstop active routing must be running the same JUNOS software release.

Nonstop Active Routing Protocol and Feature Support

Table 9 lists the protocols that are supported by nonstop active routing.

Table 9: Nonstop Active Routing Protocol and Feature Support

Note: Layer 3 VPN support does not include RSVP-based tunnels, dynamic GRE tunnels, multicast VPNs, or BGP flow routes. The following OSPF features and configuration statements are also not supported: domain-id domain-id statement at the [edit routing-instances routing-instance-name protocols (ospf | ospf3)] hierarchy level domain-vpn-tag number statement at the [edit routing-instances routing-instance-name protocols (ospf | ospf3)] hierarchy level metric number statement at the [edit routing-instances routing-instance-name protocols ospf area area-id sham-link-remote] hierarchy level sham-link local address statement at the [edit routing-instances routing-instance-name protocols ospf] hierarchy level sham-link-remote address <metric number> statement at the [edit routing-instances routing-instance-name protocols ospf area area-id] hierarchy level

Note: If you configure a protocol that is not supported by nonstop active routing, the protocol operates as usual. When a switchover occurs, the state information for the unsupported protocol is not preserved and must be refreshed using the normal recovery mechanisms inherent in the protocol.

Note: On routers that have logical systems configured on them, only the master logical system supports nonstop active routing.

Nonstop Active Routing BFD Support

Nonstop active routing supports the bidirectional forwarding detection (BFD) protocol, which uses the topology discovered by routing protocols to monitor neighbors. The BFD protocol is a simple hello mechanism that detects failures in a network. Because BFD is streamlined to be efficient at fast liveliness detection, when it is used in conjunction with routing protocols, routing recovery times are improved. With nonstop active routing enabled, BFD session states are not restarted when a Routing Engine switchover occurs.

Note: BFD session states are saved only for clients using aggregate or static routes or for BGP, IS-IS, or OSPF/OSPFv3.

When a BFD session is distributed to the Packet Forwarding Engine, BFD packets continue to be sent during a Routing Engine switchover. If non-distributed BFD sessions are to be kept alive during a switchover, you must ensure that the session failure detection time is greater than the Routing Engine switchover time. The following BFD sessions are not distributed to the Packet Forwarding Engine: multi-hop sessions, tunnel-encapsulated sessions, and sessions over aggregated Ethernet and Integrated Routing and Bridging (IRB) interfaces.

Note: For BFD sessions to remain up during a Routing Engine switchover event when nonstop active routing is configured, the value for the minimum-interval configuration statement (a BFD liveness detection parameter) must be at least 2500 ms for Routing Engine-based sessions and at least 10 ms for distributed BFD sessions.

Nonstop Active Routing BGP Support

If the BGP peer in the master routing engine has negotiated address-family capabilities that are not supported for nonstop active routing, then the corresponding BGP neighbor state on the backup routing engine shows as idle. On switchover, the BGP session is reestablished from the new master routing engine.

Only the following address families are supported for nonstop active routing:

• inet unicast
• inet labeled-unicast
• inet multicast
• inet6 labeled-unicast
• inet6 multicast
• inet6 unicast
• route-target
• l2vpn signaling
• inet6-vpn unicast
• inet-vpn unicast

Nonstop Active Routing Layer 2 Circuit and LDP-Based VPLS Support

Nonstop active routing supports Layer 2 circuit and LDP-based VPLS, which enables the backup Routing Engine to track the label advertised by Layer 2 circuit and LDP-based VPLS on the primary Routing Engine, and to use the same label after the Routing Engine switchover.

Nonstop Active Routing PIM Support

Nonstop active routing supports Protocol Independent Multicast (PIM) with stateful replication on backup Routing Engines. State information replicated on the backup Routing Engine includes information about neighbor relationships, join and prune events, rendezvous point (RP) sets, synchronization between routes and next hops, and the forwarding state between the two Routing Engines.

To configure nonstop active routing for PIM, include the same statements in the configuration as for other protocols: the nonstop-routing statement at the [edit routing-options] hierarchy level and the graceful-restart statement at the [edit chassis redundancy] hierarchy level. To trace PIM nonstop active routing events, include the flag nsr-synchronization statement at the [edit protocols pim traceoptions] hierarchy level.

Note: The clear pim join, clear pim register, and clear pim statistics operational mode commands are not supported on the backup Routing Engine when nonstop active routing is enabled.

Nonstop active routing support varies for different PIM features. The features fall into the following three categories: supported features, unsupported features, and incompatible features.

Supported features:

• Auto-RP
• BFD
• Bootstrap router
• Dense mode
• Sparse mode (except for some subordinate features mentioned in the following list of unsupported features)
• Source-specific multicast (SSM)
• Static RPs

Unsupported features: You can configure the following PIM features on a router along with nonstop active routing, but they function as if nonstop active routing is not enabled. In other words, during Routing Engine switchover and other outages, their state information is not preserved and traffic loss is to be expected.

• Internet Group Management Protocol (IGMP) exclude mode
• IGMP snooping
• PIM for IPv6 and related features such as embedded RP and Multicast Listener Discovery (MLD)
• Policy features such as neighbor policy, bootstrap router export and import policies, scope policy, flow maps, and reverse path forwarding (RPF) check policies.
• Upstream assert synchronization

Incompatible features: Nonstop active routing does not support the following features, and you cannot configure them on a router enabled for PIM nonstop active routing. The commit operation fails if the configuration includes both nonstop active routing and one or more of these features:

• Anycast RP
• Draft-Rosen multicast VPNs (MVPNs)
• Local RP
• Next-generation MVPNs with PIM provider tunnels
• PIM join load balancing

JUNOS software provides a configuration statement that disables nonstop active routing for PIM only, so that you can activate incompatible PIM features and continue to use nonstop active routing for the other protocols on the router. Before activating an incompatible PIM feature, include the nonstop-routing disable statement at the [edit protocols pim] hierarchy level. Note that in this case nonstop active routing is disabled for all PIM features, not only incompatible features.

Nonstop Active Routing Support for RSVP-TE LSPs

The JUNOS software extends non-stop active routing support to transit label-switching routers (LSR) that are part of an RSVP-TE LSP. Non-stop active routing support on transit LSRs ensures that the master to backup Routing Engine switchover on an LSR remains transparent to the network neighbors and that the LSP information remains unaltered during and after the switchover. You can use the show rsvp version command to find out the non-stop active routing mode and state on a label-switching router.

However, the JUNOS software does not support the following features for non-stop active routing on RSVP-TE transit and egress LSRs:

• Point-to-multipoint (P2MP) LSPs
• Generalized Multiprotocol Label Switching (GMPLS) and LSP hierarchy
• Inter-domain or loose hop expansion LSPs
• Ingress features such as circuit cross connect (CCC), LSP advertising, LDP tunneling, etc are not supported. Similarly, ingress bypass LSPs are also not supported for nonstop active routing..

Nonstop active routing support for RSVP-TE LSPs is subject to the following limitations and restrictions:

• Control plane statistics corresponding to show rsvp statistics and show rsvp interface detail | extensive commands are not maintained across routing engine switchovers.
• Statistics from the backup routing engine are not reported for show mpls lsp statistics and monitor mpls label-switched-path commands. However, if a switchover happens, the backup routing engine, after taking over as the master, starts reporting the statistics. Note that the clear statistics command issued on the old master routing engine does not have any effect on the new master routing engine, which reports statistics including any uncleared statistics.
• State timeouts may take additional time during nonstop active routing switchover. For example, if a switchover happens after a neighbor has missed two hello messages to the master, the new master routing engine waits for another three hello periods before timing out the neighbor.
• When nonstop active routing is enabled, graceful restart is not supported. However, graceful restart helper mode is supported along with nonstop active routing.