Wired Intelligent Edge

So I've seen some conflicting info on configuring LACP trunks between Aruba and Cisco, particularly pertaining to channel group mode on Cisco.  What we have inherited is a Cisco shop which we are slowly transitioning to Aruba, which means we will have both devices in some locations.  In this example, we are replacing an end of life Cisco Catalyst C2960S switch with an Aruba 2930F.  Currently there is an EtherChannel consisting of 2 fiber links which originates on the distribution switch, which is to be replaced, and terminates at a Cisco access switch stack with 1 fiber link going to each stack member.  The question is how to configure the Aruba's LACP so it can talk to the Cisco.  Below are config snippets with swt1 being the distribution switch and swt2 being the access switch stack.

swt1#sh run

interface Port-channel5
description Port channel 5
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root
!
interface GigabitEthernet1/0/25
description Port channel 5 > swt2
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root
channel-group 5 mode active
!
interface GigabitEthernet1/0/26
description Port channel 5 > swt2
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root
channel-group 5 mode active

swt2#sh run

interface Port-channel5
description Port channel 5
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard loop
!
interface GigabitEthernet1/0/49
description Port channel 5 > swt1
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard loop
channel-protocol lacp
channel-group 5 mode active
!
interface GigabitEthernet2/0/49
description Port channel 5 > swt1
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard loop
channel-protocol lacp
channel-group 5 mode active

Thank you in advance for any help you can give.

Hi,

You need to add trunk (TrkX) and attach interface port on this trunk

and after tag vlan on Trunk (vlan XXX tagged TrkYY)

Thanks for your reply.  I searched before I posted and found this post from 2016.  https://community.arubanetworks.com/t5/ArubaOS-and-Controllers/EtherChannel-between-Aruba-and-Cisco-switch/td-p/438

Not exactly the same hardware, but are you aware of any issues with channel group mode on the Cisco side?

Pretty strange that on swt1 (Cisco, Distribution layer):

interface Port-channel5
description Port channel 5
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root

interface GigabitEthernet1/0/25
description Port channel 5 > swt2
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root
channel-group 5 mode active

interface GigabitEthernet1/0/26
description Port channel 5 > swt2
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk
spanning-tree guard root
channel-group 5 mode active

Gigabit Ethernet interfaces 1/0/25 and 1/0/26 haven't the "channel-protocol lacp" explicitly declared (as on swt2, Access layer) although they both were declared to be members of "channel-group 5 mode active"

That's just a doubt about how the EtherChannel (link aggregation) was formed between Cisco switches.

As per VLAN membership:

switchport trunk encapsulation dot1q
switchport trunk native vlan 999
switchport trunk allowed vlan 30,100,1130,1200
switchport mode trunk

the corresponding ArubaOS-Switch configuration just requires that you set the VLANs memberships of the Aruba's Port Trunk as @alagoutte wrote:

vlan 999 untagged trk<TRK-ID> (for the native untagged VLAN)

vlan 30 tagged trk<TRK-ID>

vlan 100 tagged trk<TRK-ID>

vlan 1130 tagged trk<TRK-ID>

vlan 1200 tagged trk<TRK-ID>

Or, if you want to achieve the same outcome by using just two commands:

interface ethernet trk<TRK-ID> untagged 999

interface ethernet trk<TRK-ID> tagged 30,100,1130,1200

We suppose your Port Trunk trk<TRK-ID> is going to be configured as LACP:

trunk ethernet <1st-interface-ID>,<2nd-interface-ID> trk<TRK-ID> lacp

Also, have a look at this document.

Thank you for the clarification and the link to that doc.

I noticed the channel protocol discrepancy too.  I just chalked it up to the charming Cisco feature whereby if the channel mode is set to active (or passive), the channel uses LACP since those are the only modes available to LACP.  It makes the protocol declaration superfluous, but I like having it specifically declared if for no other reason than documentation.  Obviously, it will be declared on the Aruba trunk.

Also, the encapsulation command won't be necessary as newer Cisco's don't support ISL and 802.1Q is the default.

Anyway, I believe I know how to configure these devices now.  I'll report back here with my experience.  Thank you all.

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@macellaio wrote: I noticed the channel protocol discrepancy too.  I just chalked it up to the charming Cisco feature whereby if the channel mode is set to active (or passive), the channel uses LACP since those are the only modes available to LACP.  It makes the protocol declaration superfluous, but I like having it specifically declared if for no other reason than documentation.

I agree with you, it looks like the protocol declaration would be automatically derived by the fact that the active mode could only be related to LACP and there is no similar concept on non protocol based link aggregations such as static ones (HP/Aruba non protocol based link aggregations are called simply "trunk" instead of "lacp", not an happy option name when you're configuring a Port Trunk with the trunk command starting with the word "trunk" too...but it's OK if you already know that...this generated and generates a lot of confusion...an option named, as example, "non-protocol" would have been better IMHO).

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@macellaio wrote: Anyway, I believe I know how to configure these devices now.  I'll report back here with my experience.  Thank you all.

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Great!

One last question for clarification.  Do I need to set the trunked interfaces on the Aruba to active mode to match the Cisco configuration?

int 25-26 lacp active

No, you don't need to do that (lacp active): if you will use lacp active you will end up with a "Dynamic" LACP Port Trunk (the logical interface will be labelled as Dyn<Trunk-ID> and not as Trk<Trunk-ID> as per "Static" LACP or per "Static" Non Protocol port trunking methods).

Here the lacp "active" option means more "dynamic" lacp versus "static" lacp.

Please note that Dynamic LACP trunks operate only in the default LAN (unless GVRP is enabled and Forbid is used to prevent the trunked ports from joining the default VLAN).

Thus, if an LACP dynamic port forms using ports that are not in the default VLAN, the trunk automatically moves to the default VLAN unless GVRP operation is configured to prevent this from occurring. In some cases, this can create a traffic loop in your network.

So YMMV...but I've never used the lacp active (so Dyn<Trunk-ID>) and I never had any issue in forming the LACP with my peers (Servers or other Switches).

I admit there is some sort of confusion because, in terms of links aggregation, you could deal with three scenarios (the third was - at least for me - never used at all):

• Trunk AKA "Non Protocol" (basically "static" port trunking with no aggregation control protocol such as the famous LACP) -> logical interface will be labelled as Trk<Trunk-ID>
• LACP (basically "static" not necessarily passive, IMHO it's active) -> logical interface will be labelled as Trk<Trunk-ID>
• LACP active (basically "dynamic" necessarily active) -> logical interface will be labelled as Dyn<Trunk-ID>

Have a look to Aruba 2930F / 2930M Management and Configuration Guide for ArubaOS-Switch 16.10 (Chapter 5 "Port Trunking" starting from page 118 of 759) of October 2019, Edition 1 and you should be able to recognize what I summed up above.