CBS350 - DHCP Server stops working after reboot

[CeeKayOne]

Hello Forum,

I'm encountering a problem, where the configured DHCP server within our CBS350 stops working after a reboot of the swtich. We have updated the firmware to the latest 3.4.0.17 release and performed a restore of the factory defaults. The problem remains. I also have found similar topics with different models, but non provided a solution. 

Here is what we do to reproduce the error

1. Factory Rest of CBS350

2. Create user account and log into CBS

3. Switch to advanced view

4. IPv4 Configuration -> IPv4 Interface - Delete VLAN1 interface with the DHCP IP adress type

5. IPv4 Configuration -> DHCP Server -> Properties -> Enable DHCP server and save to startup configuration

6. IPv4 Configuration -> DHCP Server -> Network Pools -> Create a new pool

apply and save to startup configuration.

Right now our devices will receive a DHCP adress from the switch. 

7. Reboot switch -> Switch will not distribute DHCP leases anymore. 

I would bet that it is a minor configuration problem that I'm missing, but I can't figure out which one. Any ideas?

Best regards,

Chris

[marce1000]

          - FYI : https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwj59319
                        Well that one doesn't seem to help....

            + For sanity , check when in that situation the DHCP requests are still received on the device (through logs)
              And also check if there is any activity from the DHCP server , at all

           Looks like with this nice bug report you may need to escalate :
                  https://www.cisco.com/c/en/us/support/web/tsd-cisco-small-business-support-center-contacts.html

   M.

[CeeKayOne]

Thank you Marce for the reply. 

Indeed according to wireshark traffic records the DHCP in the CBS seems to stop working. This is the traffic with a fresh configuration

and here you can see what happens after a reboot

unfortunately the bug report you mentioned might not effect only the 3.4.x firmwares. I tried reverting the firmware to 3.2.x and the DHCP bug is still present. So yeah might have to escalate.

[marce1000]

   - Yeah , you may need support ; I myself never like DHCP services on switches because they present a possible
      race condition when offering network services , you could even consider a simple Linux based VM to configure that
     (being reachable for the particular network segment(s))

    High end businesses will choose for DHCP-appliances which vendors can offer in 'cluster format' , so always have one
    available when needed (e.g.) and keeping a replicated version of the dhcp lease database 'as partners'

 M.

[KJK99]

@CeeKayOne 

I don't think that would happen if the switch was configured properly. The DHCP server issue in CBS350 is of a different kind. Its configuration gets corrupted when changes are made to its SVIs when the DHCP server is enabled. That doesn't seem to be your case.

"4. IPv4 Configuration -> IPv4 Interface - Delete VLAN1 interface with the DHCP IP address type."

Why do you do that? The switch needs an IP address. Also, its IP address in the VLAN where you want to use the DHCP server needs to be static and outside of the DHCP address pool range. The IPv4 routing may need to be enabled, too, but I'm not sure about it right now. 

[CeeKayOne]

Hello Kris,

our goal is an isolated network for Dante audio devices. Therefore the CBS switch is supposed to work as a standalone device without any connection to other devices or networks besides those Dante devices. This is why we want it to work as a DHCP server. 

Regarding the step no 4, where I delete the DHCP labled default VLAN1. This seems to be mandatory cause otherwise the GUI will tell you that the DHCP can not be enabled. Otherwise I think that Option3 is what you mean with the router needs a static IP outside the DHCP pool. I would suspect that this option takes care of this. 

[KJK99]

If you want a DHCP server in a VLAN on CBS350, you need an SVI in that VLAN on the switch and its IP address needs to be static.

Have you seen this Audinate document?

https://audinateweb.sfo2.cdn.digitaloceanspaces.com/wp-content/uploads/2022/11/Managed-Switch-Tutorial-CBS350-8FP-2G-v1.00.pdf