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Preparing for a Unified ISSU in a Virtual Chassis

You can perform a unified in-service software upgrade (unified ISSU) in an Virtual Chassis. Before you begin such an upgrade, perform the following tasks to help ensure its success.

Note:

For recommended settings on Virtual Chassis devices, please consult Maximizing Scaling and Performance for MX Series Virtual Chassis on the Juniper Networks Knowledge Base.

To prepare for a unified ISSU in a two-member Virtual Chassis:

  1. Back up the existing system software to each member router’s hard disk so you can roll back to it if necessary.

    Isssue the request system snapshot all-members command to archive data and executable areas for all members of the Virtual Chassis configuration.

  2. Make sure enhanced IP network services is configured.

    See Example: Configuring Interchassis Redundancy for MX Series 5G Universal Routing Platforms Using a Virtual Chassis.

  3. Verify that both graceful Routing Engine switchover (GRES) and nonstop active routing (NSR) are enabled.

    See Example: Configuring Interchassis Redundancy for MX Series 5G Universal Routing Platforms Using a Virtual Chassis.

  4. Make sure the router is configured to delay for 180 seconds (3 minutes) before removing access routes and access-internal routes for DHCP and PPP subscriber management after a graceful Routing Engine switchover takes place.

    See Minimize Traffic Loss Due to Stale Route Removal After a Graceful Routing Engine Switchover.

  5. Ensure that the router is configured to use a hold-time value of 300 seconds when negotiating a BGP connection with the peer.

    See BGP Messages Overview.

  6. Stop all CPU-intensive periodic operations running on the Virtual Chassis in order to conserve system resources.

    Examples of such CPU-intensive operations include, but are not limited to, periodic SNMP Get and SNMP Walk requests, isssuing Junos OS operational mode commands with detailed or extensive output, and runnning Stylesheet Language Alternative Syntax (SLAX) operational scripts that monitor device status or network events.

  7. (Aggregated Ethernet interfaces only) If you are using aggregated Ethernet interfaces, make sure each interface is configured to use a slow interval (every 30 seconds) for periodic transmission of Link Aggregation Control Protocol (LACP) packets.

    See Configuring LACP for Aggregated Ethernet Interfaces.

  8. (IS-IS interfaces only) If you are using IS-IS interfaces configured with the iso protocol family, make sure the link-state PDU lifetime value (lsp-lifetime) is set to 65317 seconds.

    See Example: Configuring the Transmission Frequency for Link-State PDUs on IS-IS Interfaces.

Best Practice:

For additional information about unified ISSU, consult our Knowledge Base.

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