Forum Discussion
smp_86112
Cirrostratus
CirrostratusProper Trunk/Etherchannel LACP Configuration
I'm working with LACP and trunks for the first time on a 10.1.0 LTM box. I have read the TMOS Config Guide, and there is some ambiguity around the proper way to configure LACP between the trunk and the etherchannel on the switch.
First, is it better to have the Cisco run Active and the LTM Passive? Cisco Passive and LTM Active? Or both Active?
I (finally) have this working with the Cisco Active and the LTM Passive. But if I display the etherchannel details, the output shows the Cisco is sending "Slow LACPDUs". Network traces show that the frames are send at a frequency of ~7 seconds. Is there a way to increase this frequency?
The TMOS Config Guide states the LTM can send these LACP frames every second using a Short Timeout.
My preference is to send these frames every second. Assuming both sides should not be Active, that means the Cisco will need to run Passive.
Or should they both run Active? The TMOS Config Guide isn't clear on this. I'd appreciate your input.
6 Replies
- Just to make sure, What's your channel-protocol on the cisco port configured as?
I've always used active/active, it's reccomened...
Not an end all doc to 802.3ad, but some info.. (from the below link)
LACP trunking supports four modes of operation, as follows:
On: The link aggregation is forced to be formed without any LACP negotiation .In other words, the switch will neither send the LACP packet nor process any incoming LACP packet. This is similar to the on state for PAgP.
Off: The link aggregation will not be formed. We do not send or understand the LACP packet. This is similar to the off state for PAgP.
Passive: The switch does not initiate the channel, but does understand incoming LACP packets. The peer (in active state) initiates negotiation (by sending out an LACP packet) which we receive and reply to, eventually forming the aggregation channel with the peer. This is similar to the auto mode in PAgP.
Active: We are willing to form an aggregate link, and initiate the negotiation. The link aggregate will be formed if the other end is running in LACP active or passive mode. This is similar to the desirable mode of PAgP.
There are only three valid combinations to run the LACP link aggregate, as follows:
active
active
Comments- Recommended.
active
passive
comments- Link aggregation occurs if negotiation is successful.
on
on
comments- Link aggregation occurs without LACP. Although this works, it is not recommended.
Note: By default, when an LACP channel is configured, the LACP channel mode is passive.
http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094470.shtml 
HamishCirrocumulus
I run all mine (That have channels configured) as active/active. FWIW as a comparison we run some ESX servers with etherchannel too. They have to run on/on because ESX doesn't do LACP... We have no end of troubles with ESX (Because there's no way for the switch and the host to detect cabling errors). 0 problems with BigIP and LACP...
H
smp_86112The interfaces are configured in active mode - this is the running config of one interface in the group:
interface FastEthernet0/21
switchport access vlan 100
switchport mode access
speed 100
duplex full
udld port
channel-group 10 mode active
end
What I'm hearing is that I should be running Active/Active with a Short LTM Timeout. It doesn't appear there is any way to change the Cisco timeout on a 3550?- Nice tip on the ESX servers...
Can you post your port channel config as well please please?
Is this working for you? Your switchport mode should be trunk... - smp_86112Thanks for asking. It seems to be working from my perspective. By that, I mean it is behaving how I would expect. We can shut one port in the channel without disruption, and shutting down both ports triggers VLAN Failsafe. This is the running config of the channel and both ports - we are not using tagged interfaces on the LTM side:
interface Port-channel10
switchport access vlan 100
switchport mode access
end
interface FastEthernet0/21
switchport access vlan 100
switchport mode access
speed 100
duplex full
udld port
channel-group 10 mode active
end
interface FastEthernet0/23
switchport access vlan 100
switchport mode access
speed 100
duplex full
udld port
channel-group 10 mode active
end - K, you should be fine if you're not looking to tag through the ports.... You may want to set it up as a trunk in case you have a need in the future for multiple vlans etc... That way you won't have to disturb production.. (if indeed it is)..
