Configure Unified ISSU for 802.1ag CFM

A unified in-service software upgrade (ISSU) enables you to upgrade between two different Junos OS releases with no disruption on the control plane and with minimal disruption of traffic. Unified ISSU is automatically enabled for the Connectivity Fault Management (CFM) protocols and interoperates between local and remote maintenance endpoints (MEPs).

The Junos OS provides support for unified ISSU using the loss threshold type length value (TLV), which is automatically enabled for CFM. TLVs are described in the IEEE 802.1ag standard for CFM as a method of encoding variable-length and optional information in a protocol data unit (PDU). The loss threshold TLV indicates the loss threshold value of a remote MEP. The loss threshold TLV is transmitted as part of the CFM continuity check messages.

During a unified ISSU, the control plane may go down for several seconds and cause CFM continuity check packets to get dropped. This may cause the remote MEP to detect a connectivity loss and mark the MEP as down. To keep the MEP active during a unified ISSU, the loss threshold TLV communicates the minimum threshold value the receiving MEP requires to keep the MEP active. The receiving MEP parses the TLV and updates the loss threshold value, but only if the new threshold value is greater than the locally configured threshold value.

An overview of CFM is described starting in IEEE 802.1ag OAM Connectivity Fault Management Overview, and you should further observe the additional requirements described in this topic.

Table 1 shows the Loss Threshold TLV format.

Junos OS provides configuration support for the convey-loss-threshold statement, allowing you to control the transmission of the loss threshold TLV in continuity check messages PDUs. The convey-loss-threshold statement specifies that the loss threshold TLV must be transmitted as part of the continuity check messages. If the convey-loss-threshold statement is not specified, continuity check messages transmit this TLV only when a unified ISSU is in progress. The Junos OS provides this configuration at the continuity-check level. By default, continuity check messages do not include the loss threshold TLV.

To configure the convey loss threshold, use the convey-loss-threshold statement at the [edit protocols oam ethernet connectivity-fault-management maintenance-domain identifier maintenance-association identifier continuity-check] hierarchy level.

For the remote MEP, the loss threshold TLV is transmitted only during the unified ISSU if the convey-loss-threshold statement is not configured. The remote MEP switches back to the default loss threshold if no loss threshold TLV is received or the TLV has a default threshold value of 3.

An example of the ISSU configuration statements follows:

protocols {
    oam {
        ethernet {
            connectivity-fault-management {
                maintenance-domain identifier {
                level number;
                    maintenance-association identifier {
                        continuity-check {
                            convey-loss-threshold; 
                            interval number;
                            loss-threshold number;
                            hold-interval number;
                        }
                    }
                }
            }
        }
    }
}

The Junos OS saves the last received loss threshold TLV from the remote MEP. You can display the last saved loss threshold TLV that is received by the remote MEP, using the show oam ethernet connectivity-fault-management mep-database maintenance-domain identifier maintenance-association identifier local-mep identifier remote-mep identifier command, as in the following example:

user@host> show oam ethernet connectivity-fault-management mep-database maintenance-domain md3 maintenance-association ma5 local-mep 2 remote-mep 1
Maintenance domain name: md3, Format: string, Level: 3
  Maintenance association name: ma3, Format: string
  Continuity-check status: enabled, Interval: 1s, Loss-threshold: 3 frames
  MEP identifier: 2, Direction: up, MAC address: 00:19:e2:b0:76:be
  Auto-discovery: enabled, Priority: 0
  Interface status TLV: none, Port status TLV: none
  Connection Protection TLV: yes
    Prefer me: no, Protection in use: no, FRR Flag: no
  Interface name: xe-4/1/1.0, Interface status: Active, Link status: Up
    Loss Threshold TLV:                          
      Loss Threshold: 3  , Flag:    0x0

 Remote MEP identifier: 1, State: ok
    MAC address: 00:1f:12:b7:ce:79, Type: Learned
    Interface: xe-4/1/1.0
    Last flapped: Never
    Continuity: 100%, Admin-enable duration: 45sec, Oper-down duration: 0sec
    Effective loss threshold: 3 frames  
    Remote defect indication: false
    Port status TLV: none
    Interface status TLV: none
    Connection Protection TLV:
      Prefer me: no, Protection in use: no, FRR Flag: no
    Loss Threshold TLV:   #Displays last received value                
      Loss Threshold: 3  , Flag:    0x0

The Junos OS saves the last transmitted loss threshold TLV from a local MEP. You can display the last transmitted loss threshold TLV and the effective loss (operational) threshold for the remote MEP, using the show oam ethernet connectivity-fault-management mep-database maintenance-domain identifier maintenance-association identifier local-mep identifier remote-mep identifier command, as in the following example:

user@host> show oam ethernet connectivity-fault-management mep-database maintenance-domain md3 maintenance-association ma5 local-mep 2 remote-mep 1
Maintenance domain name: md3, Format: string, Level: 3
  Maintenance association name: ma3, Format: string
  Continuity-check status: enabled, Interval: 1s, Loss-threshold: 3 frames
  MEP identifier: 2, Direction: up, MAC address: 00:19:e2:b0:76:be
  Auto-discovery: enabled, Priority: 0
  Interface status TLV: none, Port status TLV: none
  Connection Protection TLV: yes
    Prefer me: no, Protection in use: no, FRR Flag: no
  Interface name: xe-4/1/1.0, Interface status: Active, Link status: Up
    Loss Threshold TLV:   #Displays last transmitted value      
      Loss Threshold: 3  , Flag:    0x0
 
   Remote MEP identifier: 1, State: ok
    MAC address: 00:1f:12:b7:ce:79, Type: Learned
    Interface: xe-4/1/1.0
    Last flapped: Never
    Continuity: 100%, Admin-enable duration: 45sec, Oper-down duration: 0sec
    Effective loss threshold: 3 frames   #Displays operational threshold    
    Remote defect indication: falsePort status TLV: none
    Interface status TLV: none
    Connection Protection TLV:
      Prefer me: no, Protection in use: no, FRR Flag: no
    Loss Threshold TLV:                  
      Loss Threshold: 3  , Flag:    0x0