C9600 w/ SUP1 SVL. Can I use portchannel 127 and 128

a12288 · ‎07-08-2025

On "Configuring Cisco StackWise Virtual" document. It says "Etherchannel 127 and 128 are reserved for SVL connections". but the later configuration did not mention configure etherchannel 127 and 128 rather just specify 2 interfaces as SVL link.

My question is can I use port channel 127 and 128, as overall it only supports 192 port channels. Thanks.

julian.bendix · ‎07-08-2025

Hey!

Yes, as far as I know only 190 Port-Channels are really possible and 127 + 128 are created under the hood for DAD and SVL Links.

Should be the same for C9400, for which I quickly found the following in Cisco Live Slides:

https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2023/pdf/BRKENS-2095.pdf

• StackWise Virtual EtherChannel Support
• C9400: Support 252 port-channel with IOS-XE
16.12 or later
• Port channel ID 127 and 128 are reserved for SVL
• Port channel ID 1-126 and 129-252 are available for L2/L3
network configuration

• All other C9K platforms: Support 128 port-channel
• Port channel ID 128 is reserved for SVL
• Port channel ID 1-127 are available for L2/L3 network
configurations

Unfortunately it does not reflect the C9600 - hope it still helps.

BR Jules

wajidhassan · ‎07-08-2025

No, you cannot use port-channels 127 and 128 for anything else when StackWise Virtual is enabled. These port-channel numbers are reserved internally by the system for StackWise Virtual Link (SVL) operation, even if you don’t explicitly configure them as port-channels. This reservation ensures high availability and system synchronization between the two supervisors.

If you're planning your port-channel usage, you effectively have port-channel IDs 1–126 and 129–192 available for regular use. Avoid manually assigning 127 or 128 to any LAGs to prevent conflicts or unexpected behavior.

MHM Cisco World · ‎07-08-2025

show interface port-channel128
show interface port-channel127

These PO auto generate to check

Do show command and see

MHM

a12288 · ‎07-09-2025

I just setup a brand new pair of SVL, with basic SVL config and nothing else, but I did not see PO127 or PO128. I'm running 17/09/06a.

LAB-SWL-JNHN#sh stackwise-virtual link
Stackwise Virtual Link(SVL) Information:
----------------------------------------
Flags:
------
Link Status
-----------
U-Up D-Down
Protocol Status
---------------
S-Suspended P-Pending E-Error T-Timeout R-Ready
-----------------------------------------------
Switch SVL Ports Link-Status Protocol-Status
------ --- ----- ----------- ---------------
1 1 HundredGigE1/1/0/41 U R
HundredGigE1/6/0/41 U R
2 1 HundredGigE2/1/0/41 U R
HundredGigE2/6/0/41 U R

LAB-SWL-JNHN#sh int po 127
^
% Invalid input detected at '^' marker.

LAB-SWL-JNHN#sh int po 128
^
% Invalid input detected at '^' marker.

LAB-SWL-JNHN#sh etherchannel 127 sum
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port

A - formed by Auto LAG

Number of channel-groups in use: 0
Number of aggregators: 0

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------

LAB-SWL-JNHN#sh etherchannel 128 sum
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port

A - formed by Auto LAG

Number of channel-groups in use: 0
Number of aggregators: 0

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------

LAB-SWL-JNHN#

LAB-SWL-JNHN#sh etherchannel sum
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
d - default port

A - formed by Auto LAG

Number of channel-groups in use: 0
Number of aggregators: 0

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------

a12288 · ‎07-09-2025

Ok, I opened a Cisco TAC case to help me clear the water, here is the summary:

At SVL config, we all know we cannot use PO127 or Po128
Neither in configuration nor any show command(s) will display anything about SVL ports or PO127/PO128

So the bottom line is just pick couple or several interfaces and configure them as SVL link, and that's IT! Assumingly behind the scenes the Po127 & 128 are created automatically, though we have no way to confirm or verify.

For argument's sake, should you try to use Po 127 or 128, you won't be successful but get error message like "LAB-SWL-JNHN(config)#int po 127
Port-channel group 127 is reserved."

According to the TAC, all the reasons behind this is to force us not to use Po127 & 128. So fair enough I assume.

MHM Cisco World · ‎07-09-2025

NO show command can help us here ?

MHM

julian.bendix · ‎07-09-2025

@MHM Cisco World no, they won't show up under any show commands...