LACP (LAG) interoperability between the EX Series Switches and Catalyst 6400 Series Switches.

A number of interfaces in a Link Aggregation Group (LAG) are not parsing traffic, resulting in packet loss.  Removing and re-adding links to the aggregate does not resolve the issue.

This scenario is for a LACP config with 4 interfaces in the LAG between the EX4200 Virtual Chassis (VC) and Cisco Catalyst 6500.

When the aggregated links are brought online the immediate packet loss is about 60% from a number of PC endpoints (in different subnets but all on the same VLAN)

When we take a link out of the LAG, the response improves marginally.  Taking another link out of the aggregate makes no difference.  There are now 2 links in the aggregate.  Removing the 3rd link results in 1 link left in the aggregate and 100% ping, no more packet loss.

When a second link was re-added, the LAG was still 100% ping success and no packet loss.

A third link was re-added to the LAG, and packet loss occurs.

That same link was removed and re-added with no improvment.  A fourth link was re-added and there was no improvement.

EX Switch:

prompt> show lacp interfaces ae <interfacenumber>

The output will look similar to this example:

user@switch> show lacp interfaces ae1

Aggregated interface: ae1
LACP state:   Role     Exp   Def   Dist   Col   Syn   Aggr   Timeout Activity
ge-0/0/0         Actor     No    No    Yes    Yes   Yes  Yes     Fast Passive
ge-0/0/0         Partner No    No    Yes    Yes   Yes  Yes    Slow Active
ge-1/0/0         Actor     No    No     No      No    No   Yes     Fast Passive
ge-1/0/0         Partner No    No     No     No     Yes Yes    Slow Active
ge-3/0/0         Actor     No    No     No      No     No   Yes    Fast Passive
ge-3/0/0         Partner No    No     No     No     Yes  Yes    Slow Active
ge-4/0/0         Actor     No    No     No     No      No   Yes    Fast Passive
ge-4/0/0         Partner No    No     No     No     Yes  Yes    Slow Active

LACP protocol:  Receive State   Transmit State   Mux State
ge-0/0/0 Current Slow periodic Collecting distributing
ge-1/0/0 Current Slow periodic Detached
ge-3/0/0 Current Slow periodic Detached
ge-4/0/0 Current Slow periodic Detached

Please check the key value on the interfaces in the aggregate by command:

prompt> monitor interface <interfaceID> extensive

The output should look similar to the following:

monitor traffic interface ge-0/0/0 extensive …>>>>>

Actor Information TLV (0x01), length 20
System 0:c:31:cd:70:0, System Priority 32768, Key 11281, Port 339, Port Priority 32
State Flags [Activity, Aggregation, Synchronization, Collecting, Distributing]
0x0000: 000c 31cd 7000 2c11 0020 0153 3d00 0000
0x000f: 0214
Partner Information TLV (0x02), length 20
System 0:1f:12:3d:27:40, System Priority 127, Key 8, Port 512, Port Priority 127

monitor traffic interface ge-4/0/0 extensive

System 0:c:31:cd:70:0, System Priority 32768, Key 9601, Port 342, Port Priority 128
State Flags [Activity, Aggregation, Synchronization]
0x0000: 000c 31cd 7000 2581 0080 0156 0d00 0000
0x000f: 0214
Partner Information TLV (0x02), length 20
System 0:1f:12:3d:27:40, System Priority 127, Key 8, Port 768, Port Priority 127


monitor traffic interface ge-1/0/0 extensive
System 0:c:31:cd:70:0, System Priority 32768, Key 9601, Port 341, Port Priority 96
State Flags [Activity, Aggregation, Synchronization]
0x0000: 000c 31cd 7000 2581 0060 0155 0d00 0000
0x000f: 0214


Partner Information TLV (0x02), length 20
System 0:1f:12:3d:27:40, System Priority 127, Key 8, Port 576, Port Priority 127
State Flags [Timeout, Aggregation]
0x0000: 001f 123d 2740 0008 007f 0240 0600 0000


monitor traffic interface ge-3/0/0 extensive

System 0:c:31:cd:70:0, System Priority 32768, Key 9601, Port 340, Port Priority 64
State Flags [Activity, Aggregation, Synchronization]
0x0000: 000c 31cd 7000 2581 0040 0154 0d00 0000
0x000f: 0214
Partner Information TLV (0x02), length 20
System 0:1f:12:3d:27:40, System Priority 127, Key 8, Port 704, Port Priority 127


In the LACP BPDU , the Key is a constant value (among the parameters exchanged ) which remains unchanged on all the links which are exchanging the bpdu. Only this member is in the trunk table currently.

In the example above, out of the 4 member links only ge-0/0/0 is up (collecting distributing state).  This link has a different key value of 11281 than the rest of the links which have a value of 9601.

JUNOS does not allow users to configure port key and port priority.  However, the  Port Key and Port Priority are configurable on individual member links of etherchannel on the Catalyst.
It is likely there is some misconfiguration, which can lead to this situation. .

======================================
#channelprotocol
set channelprotocol lacp 6

#port channel
set port lacp-channel 6/19-22 600

set port lacp-channel 6/19 port-priority 128
set port lacp-channel 6/20 port-priority 128
set port lacp-channel 6/21 port-priority 128
set port lacp-channel 6/22 port-priority 128