WLC 9800L Backup Link to Switch

[mayer-felix]

Hi there,

I am new to networking and wanted to try something out. Maybe someone can help me.

I have a Cisco Catalyst 9800 Wlan Controller which is connected to a Switch with 2 Links. One 10Gbit Link and a 1Gbit Link. I want the 10Gbit link to be the link that is used when both are active. Just if the 10Gbit Link goes down, I want the 1Gbit link as a Backup link. And when the 10Gbit link is up again -> 10Gbit Link should be used.

My thoughts:

STP should detect a Loop and the 1Gbit Link would be blocked because 10Gbit Link is the better option. Then i read the following on https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9800-series-wireless-controllers/guide-c07-743627.html

"The C9800 wireless controller, like AireOS WLC, is meant to act as a Layer 2 host from a network perspective. This means that it doesn’t participate in Spanning Tree, for example. To speed up network convergence, it is recommended that you enable PortFast or PortFast trunk configuration for the uplinks on the switch where the C9800 is connected."

My question is whether it is possible for a network loop to occur and what it means that it doesn't participate in STP.

I also wanted to try following things:

• Etherchannel (but I think all links in one channel have to be of the same speed and duplex)
• flex link + (unfortunately no experience with that and haven't tried yet)

Please do not hesitate to correct me if am wrong at some point. I want to learn something

Thanks in advance for the assistance.

[chmayer]

very good exercise! I think you're on the right track...don't give up....
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9200/software/release/17-2/configuration_guide/lyr2/b_172_lyr2_9200_cg/configuring_flexlink_plus.html

have a look at this...
Good Luck

[Scott Fella]

Yeah @chmayer is on point about using or at least trying Flexlink.  You might as well test with Flexlink using portchannels as it seems better to design it either using portchannels on the 10g or else on the 2g interfaces.

[Rich R]

Will be interested to hear how this works for you - never used that feature before...
Note that it says "When port 1 comes back up, it goes into standby mode and does not forward traffic; port 2 continues forwarding traffic." so if you want to switch from 1G backup to your primary 10G port when it comes back up then you'll need something like an EEM script to do that for you otherwise you'll remain on the 1G port until it fails.

[chmayer]

https://contenthub.cisco.com/chapter.sjs?uri=%2Fsearchable%2Fchapter%2Fcontent%2Fen%2Fus%2Ftd%2Fdocs%2Fios-xml%2Fios%2Flanswitch%2Fconfiguration%2Fxe-16%2Flanswitch-xe-16-book%2Flsw-cfg-rep.html.xml&platform=Cisco%204000%20Series%20Integrated%20Servi...