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.
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#
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.
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;
}
}