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Unified ISSU Protocol Support

Unified ISSU is dependent on nonstop active routing. Table 14 lists the protocols that are supported during a unified ISSU.

Table 14: Unified ISSU Protocol Support

Protocol	Software Release
Border Gateway Protocol (BGP), except for BGP VPN services	JUNOS 9.0 or later
Intermediate System-to-Intermediate System (IS-IS)	JUNOS 9.0 or later
Label Distribution Protocol (LDP)	JUNOS 9.0 or later
LDP-based virtual private LAN service (VPLS)	JUNOS 9.3 or later
Layer 2 circuits	JUNOS 9.2 or later
Layer 3 VPNs using LDP	JUNOS 9.2 or later
Open Shortest Path First (OSPF)/OSPFv3	JUNOS 9.0 or later
Protocol Independent Multicast (PIM)	JUNOS 9.3 or later

Note: For routing protocols using bidirectional forwarding detection (BFD), when a Routing Engine switchover occurs, the BFD session state is not saved.

Unified ISSU Support for Layer 2 Control Protocol Process (L2CPD)

Unified ISSU supports the Layer 2 Control Protocol process (L2CPD) on MX-series Ethernet Services routers. In a Layer 2 bridge environment, spanning tree protocols share information about port roles, bridge IDs, and root path costs between bridges using special data frames called Bridge Protocol Data Units (BPDUs). The transmission of BPDUs is controlled by L2CPD. Transmission of hello BPDUs is important in maintaining adjacencies on the peer systems. The transmission of periodic packets on behalf of L2CPD is carried out by periodic packet management (PPM), which, by default, runs on the Routing Engine. However, you can configure the JUNOS software to run PPM on the Packet Forwarding Engine by including the delegate processing statement at the [edit routing-options ppm] hierarchy level. When the delegate processing statement is included in the configuration, L2CPD uses distributed PPM (PPMD) to move the responsibility of sending hello BPDUs to the Packet Forwarding Engine. PPMD in the Packet Forwarding Engine ensures that the BPDUs are transmitted even when the L2CPD control plane is unavailable, and keeps the remote adjacencies alive during unified ISSU.

Unified ISSU enhancements and nonstop active bridging support for L2CPD ensure that the new master Routing Engine is able to take control during unified ISSU without any disruptions in the control plane and minimize the disruptions in the Layer 2 data plane during unified ISSU.

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