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[MX] Subscriber Management: LACP fast-failover change in Junos 12.2 and above

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Article ID: KB28844 KB Last Updated: 31 Mar 2014Version: 1.0
Summary:

This article describes changes caused by the fast-failover knob in the behavior of the Link Aggregation Control Protocol (LACP) in link-protect in Junos 12.2 and above.

Symptoms:

When the active leg (collecting and distributing) is deactivated/disabled, the aggregated ether (AE) interface will flap even if there is a second leg in an “attached” state that takes over. Because the AE interface goes down, all Point-to-Point Protocol over Ethernet (PPPoE) clients built on that AE drop, causing an outage.

DUT (Dutch Text file) configuration

{master:member0-re0}[edit]
lab@RE0-brevaz-H1# run show configuration interfaces xe-2/0/0 
gigether-options {
    802.3ad ae0;
}
{master:member0-re0}[edit]
lab@RE0-brevaz-H1# run show configuration interfaces xe-14/0/0   
gigether-options {
    802.3ad ae0;
}lab@RE0-brevaz-H1# run show configuration interfaces ae0 
flexible-vlan-tagging;
aggregated-ether-options {
    lacp {
        passive;
    }
}

lab@RE0-brevaz-H1# run show lacp interfaces ae0 
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      xe-2/0/0       Actor    No    No   Yes  Yes  Yes   Yes     Fast   Passive
      xe-2/0/0     Partner    No    No   Yes  Yes  Yes   Yes     Fast    Active
      xe-14/0/0      Actor    No    No    No   No  Yes   Yes     Fast   Passive
      xe-14/0/0    Partner    No    No    No   No   No   Yes     Fast    Active
    LACP protocol:        Receive State  Transmit State          Mux State 
      xe-2/0/0                  Current   Fast periodic Collecting distributing
      xe-14/0/0                 Current   Fast periodic           Attached


lab@RE0-brevaz-H1# run show interfaces pp0.1073983745 
  Logical interface pp0.1073983745 (Index 818) (SNMP ifIndex 5608)
    Flags: Point-To-Point 0x4000 Encapsulation: PPPoE
    PPPoE:
      State: SessionUp, Session ID: 1,
      Session AC name: RE0-brevaz-H1, Remote MAC address: 00:10:95:00:00:01,
      Underlying interface: demux0.1 (Index 4331)
    Link:
      xe-2/0/0.32767
      xe-14/0/0.32767
    Input packets : 612
    Output packets: 613
  Keepalive settings: Interval 30 seconds, Up-count 1, Down-count 3
  LCP state: Opened
  NCP state: inet: Opened, inet6: Not-configured, iso: Not-configured, mpls: Not-configured
  CHAP state: Success
  PAP state: Closed
    Protocol inet, MTU: 1492
      Flags: Sendbcast-pkt-to-re, uRPF
      Addresses, Flags: Is-Primary
        Local: 192.168.1.2


If the active leg (xe-2/0/0) is deactivated/disabled, the AE interface will flap, causing the Point-to-Point
Protocol (PPP) interface to be cleared.

lab@RE0-brevaz-H1# set interfaces xe-2/0/0 disable                       

{master:member0-re0}[edit]
lab@RE0-brevaz-H1# commit 
member0-re0: 
configuration check succeeds
member1-re1: 
commit complete
member1-re0: 
commit complete
member0-re1: 
commit complete
member0-re0: 
commit complete

{master:member0-re0}[edit]
lab@RE0-brevaz-H1# run show lacp interfaces ae0          
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      xe-2/0/0       Actor    No   Yes    No   No   No   Yes     Fast   Passive
      xe-2/0/0     Partner    No   Yes    No   No   No   Yes     Fast   Passive
      xe-14/0/0      Actor    No    No   Yes  Yes  Yes   Yes     Fast   Passive
      xe-14/0/0    Partner    No    No   Yes  Yes  Yes   Yes     Fast    Active
    LACP protocol:        Receive State  Transmit State          Mux State 
      xe-2/0/0            Port disabled     No periodic           Detached
      xe-14/0/0                 Current   Fast periodic Collecting distributing

	  
	lab@RE0-brevaz-H1# run show interfaces ae0         
Physical interface: ae0, Enabled, Physical link is Up
  Interface index: 650, SNMP ifIndex: 1502
  Link-level type: Ethernet, MTU: 1522, Speed: 10Gbps, BPDU Error: None,
  MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled,
  Flow control: Disabled, Minimum links needed: 1, Minimum bandwidth needed: 0
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Current address: 00:24:dc:47:67:c0, Hardware address: 00:24:dc:47:67:c0
  Last flapped   : 2014-02-19 15:50:55 EST (00:01:04 ago)  *****FLAP 
  Input rate     : 992 bps (1 pps)
  Output rate    : 0 bps (0 pps)

  Logical interface ae0.32767 (Index 817) (SNMP ifIndex 1779)
    Flags: SNMP-Traps 0x4004000 VLAN-Tag [ 0x0000.0 ]  Encapsulation: ENET2
    Statistics        Packets        pps         Bytes          bps
    Bundle:
        Input :          7969          1        934258          992
        Output:           501          0          4122            0
    Adaptive Statistics:
        Adaptive Adjusts:          0
        Adaptive Scans  :          0
        Adaptive Updates:          0
    Protocol multiservice, MTU: Unlimited
      Flags: None  

	{master:member0-re0}[edit]
lab@RE0-brevaz-H1# run show interfaces pp0.1073983745    
error: interface pp0.1073983745 not found

{master:member0-re0}[edit]
lab@RE0-brevaz-H1#  
Cause:

This situation is caused by a fast-failover knob. If configured, the knob causes the AE member to be considered UP in any LACP state other than DETACHED. This is the default behavior in versions of Junos before 12.2 (such as 11.4X27).

In Junos 12.2 and above, the AE member is considered to be DOWN, by default, in any LACP state other than COLLECTING_DISTRIBUTING. Because the active leg that is in collecting-distributing is brought down, the AE interface is brought down until the "attached" leg becomes "collecting-distributing."

To provide the same functionality as previous versions of Junos 12.2, the fast-failover knob must be enabled in Junos 12.2 and above. The knob is in effect only when the user is deactivating/disabling the active leg on the DUT, which means that if the peer switch performs the active/disable on the active leg, the port transitions as expected.

Solution:

Enable the fast-failover knob in Junos 12.2 and above, as follows:

{master:member0-re0}[edit]
lab@RE0-brevaz-H1# show interfaces ae0 
flexible-vlan-tagging;
aggregated-ether-options {
    lacp {
        passive;
        fast-failover;
    }
}

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