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Subscriber Management Redundancy for PFE During Graceful OIR

Subscriber Management Support for PFE Graceful Online Insertion and Removal on Line card MICs (MX304-LMIC).

Use subscriber management redundancy on the Packet Forwarding Engine (PFE) for seamless online insertion and removal (OIR) on MX304 devices. Subscribers and flows are retained when an alternate PFE provides redundancy. This feature support includes the following functionalities:

  • When a PFE is made offline, all subscribers hosted on it are terminated, and their flows are deleted, except if there is redundancy provided by an alternate PFE. However, DHCP subscribers remain UP even if PFE is made offline. If the line card MIC (MX304-LMIC) comes back online, the pre-existing DHCP subscriber functionalities resume.
  • When a PFE goes offline, its subsidiary links are removed. If an aggregate interface has active members on another PFE, the subscriber flows remain intact. Statistics for terminated subscribers are reported as the PFE goes offline.
  • No new subscriber states are activated on the offline PFE. Other PFEs manage subscriber logins and logouts. The newly online PFE integrates seamlessly with other online PFEs to maintain subscriber management services.
  • There is a temporary delay in forwarding configuration for new subscribers during PFE transitions, depending on the number of active subscribers.
  • CPU utilization spikes during the offline process due to subscriber state transitions and during the online process if there are many subscribers.
  • All interfaces corresponding to LMIC being offline are transitioned DOWN. Subscriber management is active only on online PFEs.
  • The accounting statistics for subscribers are cached when PFE goes offline. The accounting statistics for the subscribers provide the accurate values across offline-online activity of the associated PFE. When PFE goes offline, the interface statistics are cleared for the subscriber.
  • The set chassis fpc <> pfe <> power <on | off> command is not supported on MX304 devices.
  • The command request chassis mic fpc-slot <> mic-slot <> <offline | online> is supported is supported on MX304 for graceful OIR.

  • [ See request chassis mic .]

The following tables describe the OIR support and impact related to various features and functionalities such as subscriber types, firewall behavior, BFS, Layer-2 and Layer-2 functionalities and telemetry.

Table 1: Subscriber Types during PFE OIR
Functionality PFE Handling
Subscribers on Gigabit Ethernet/10 Gigabit Ethernet physical interfaces:
  • When PFE goes offline, all PPPOE subscribers on those interfaces are deleted.
  • When the PFE is online, new subscribers can log in.
Aggregate Ethernet IFDs:
  • When PFE goes offline, associated members of the Aggregate Ethernet interface are removed. Subscribers on active members hosted by other PFEs remain active.
  • When the PFE comes back online, the subscriber states are restored.
L2TP Subscribers:
  • Subscribers over Service Interfaces (SI) on device such as Logistics Network Services (LNS) and Logistics Transport Services (LTS) are deleted when the PFE goes offline.
  • If the PFE is part of the L2TP forwarding path, the sessions might deactivate due to keepalive issues.
Subscribers over PS (Pseudowire Subscriber Interfaces): On Gigabit Ethernet/10 Gigabit Ethernet interfaces the subscribers over PS are deleted when the PFE goes offline.
Table 2: Layer 2 , Layer 3, and BFD during PFE OIR
Functionality PFE Handling
Bidirectional Forwarding Detection (BFD):
  • BFD sessions configured on the anchor PFE are disabled if the PFE goes offline and remains disabled until the PFE comes back online.
  • Non-anchor PFEs clean up session states when going offline and reprogram the sessions when brought back online.
Layer 2:
  • Bridge domains and Layer 2 token management are unaffected, as their states are stored per-PFE.
  • CFM (Connectivity Fault Management) sessions are reassigned to another PFE if the original PFE goes offline, that can result in a temporary interruption.
Layer 3: For routing protocols and related features (like OSPF or BFD), the PFE offline/online actions trigger necessary reprogramming.