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Known Limitations

Learn about known limitations in Junos OS Release 21.2R3 for MX Series routers.

For the most complete and latest information about known Junos OS defects, use the Juniper Networks online Junos Problem Report Search application.


  • EVPN-VXLAN ESI might result minor loop in some scenarios and could hit duplicate address detection (DAD) in IPV6. PR1619504

General Routing

  • RPD slips are noticed on MX104 devices that have large configuration load on the box with multiple services enabled. [For,example l2circuits, VPLS, L3VPN, firewall-filters configuration, and SNMP-polling.] To avoid RPD slips for longer time duration, configure the delta-export, persist-groups-inheritance, and fast-synchronize system configurations. You must reduce configuration size where possible. Remove any trace-options and reduce the logging pressure on the NAND-flash storage. Analyze the load from processes such as snmpd, mib2d, and pfed processes if you run SNMP. PR1361250

  • In case of SyncE signal loss, DPLL3 goes into the Holdover state and still the DPLL1/SYNTH1 signal output gets driven to CB. CB DPLL appears to be in the Locked state due to which INVALID QL gets generated. The output for the Current clock status is always taken from CB DPLL state, due to which the status is displayed as locked. PR1509356

  • It is possible that LFM might flap during MX-VC ISSU. PR1516744

  • Running the help apropos command in the configuration mode causes the mgd process to generate a core file. The mgd process comes back up and as long as the command does not cause issue, the process does not generate a core file. PR1552191

  • MX Series platforms do not support sFlow egress sampling of MPLS packets. PR1556659

  • The Resource deadlock avoided error message gets generated during software add on platforms that support phone-home solution for ZTP. PR1557468

  • On MX Series devices, the TTL value reported by sFlow egress sampling is equal to the TTL prior to decrement. The sFlow sampling at ingress and the sFlow sampling at egress report the same value of TTL. PR1559565

  • The eODN feature supports up to 1000 SRTE LSPs with 32,000 express segment links in TED. PR1561947

  • Dynamic next-hop tunnel statistics occurs on MX Series routers. Statistics for the traffic entering into the tunnel get incremented on the ingress FPC where traffic arrives and telemetry statistics get reported from ingress FPC. PR1567227

  • The PTP FPGA is kept in reset during BIOS boot. During Linux boot, the PTP FPGA is taken out of reset and pcie-tree is reenumerated. The Link-up/down occurs during this sequence. PR1572061

  • When you start ISSU, it is expected that the FPC restart does not get triggered by you. The ISSU can be aborted and system can be in-correct state. PR1572851

  • On MX, ISSU or upgrade with validate option might fail if there is too less disk space in /var/tmp/ in Junos. It is recommended to clear out all log files and core files before initiating upgrade with validate option (when not using no-validate option) or ISSU. It is better to clear all unwanted data using the request system storage cleanup command to clean up all unwanted data. You must ensure that there is at least 9 GB free space in var/tmp after copying VMHost package file to /var/tmp/. PR1582554

  • On deactivating the aggregated Ethernet interface, traffic loss of greater than 2 seconds occurs. This behavior is seen due to order in which the messages are processed in FPC wherein next hop change/delete is processed prior to interface down event. PR1614508

  • The spike in RPD usage is expected because of the very large scale and OCST in general but it should not affect any RPD functionality if that is the concern as telemetry streaming is the least priority task in RPD. PR1614978


  • When upgrading from Junos OS release 21.2 and earlier to Junos OS release 21.2 and later, validation and upgrade fails. You must upgrade software using the no-validate command. PR1568757


  • If the Routing Engines are not all rebooted after a network service configuration change, the rpd process might crash. PR1461468

  • With local reversion ON, there is a possibility of transit router not informing headend of RSVP disabled link when link is flapped more than once. As a woraround, remove the local-reversion configuration. PR1576979

  • When there is scaled RSVP sessions [around 21,000] and have enabled RSVP for all the interfaces,RPD process walks through all the interfaces which results into high CPU for some time, which also results LSP flap and log message on the Routing Engine switchovers. PR1600159

  • There is no traffic impact but the show route forwarding-table destination a.b.c.d command have stale entry for around 60 seconds. PR1610620

Network Management and Monitoring

  • Junos has a feature to block or deny all hidden commands. Users can get this feature by configuring the set system no-hidden-commands statement. However, when this is configured and committed Junos blocks or denies new netconf/junoscript XML sessions. As a workaround, you can delete the system no-hidden-commands statement and start the new netconf/junoscript sessions. PR1590350

Platform and Infrastructure

  • In some scenarios with MPC, major alarm and following messages are generated. This major error is triggered due to parity error, and the impacted queue might drop packets. This might impact the forwarding, to recover MPC card need to be rebooted. PR1303489

  • With a sensor being subscribed via Junos Telemetry Interface (JTI), after the interface is deleted/deactivated/disabled, the TCP connection is still established, and the show agent sensors command still shows the subscription. PR1477790

Routing Protocols

  • With max number of IFLs gets generated [4000 GRE tunnel per Packet Forwarding Engine] with following configuration:

    • family inet and associated source and destination for each tunnel.
    • Configure the allow-fragmentation statement on one endpoint of the tunnel.
    • Configure reassemble-packets on the other endpoint of the tunnel.

User Interface and Configuration

  • For the list definition as shown below: list bar { key foo; leaf foo { type uint8; } leaf baz { type string; } ,} Junos cannot parse the below configuration payload where 'leaf foo' (key as per Yang model) does not appear as a first element. { "bar": [ { "baz": "zig", "foo": 123 }, { "baz": "zag", "foo": 0 } ] } Junos understands only this kind of configuration payload as shown below where 'leaf foo' (key as per Yang model) appears as a first element. { "bar": [ { "foo": 123, "baz": "zig" }, { "foo": 0, "baz": "zag" } ] } As per Junos, the list keys are always required (must always) to precede any other siblings within a list entry and appear in the order specified by the data model. PR1616216