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Forum Discussion
On which VLAN do Smart Plus series switches send DHCP requests?
I've come to suspect that the Smart Managed Plus switches will send DHCP requests untagged on all their ports. Is this true?
The documentation doesn't seem to help here.
If I cannot configure the switches to send DHCP requests on a specific VLAN ID, this would mean I have to give them all static IP addresses, as some switches are connected to several VLANs with DHCP servers - so I wouldn't know what subnet they are on.
Thanks,
senstech
3 Replies
- No other way than using a static IP address in this use case.
The limitation is that the microcontroller on the Smart Managed Plus system does sit on all VLANs untagged, a management VLAN can't be configured. Please be aware that the static IP is reachable on all VLANs therefore, too. Ran into this as well, this is pretty braindead tbh because this is security sensitive. In my case the switch decided from one day to the other to start using my ISP's DHCP offer and suddenly the management interface was on the public internet. And my normal router got its DHCP lease removed.
This should be advertised with capital letters in the documentation.
No: Nothing the switch decides. Purely random which DHCP server does answer first when connected to a single broadcast domain. Your ISP does allow only one MAC address on the router, and is unable to provide additional public IP addresses. Affected devices fail back to ZeroConf addresses, others to default IP addresses.
For users desperate to deploy a switch - why ever, one possible reason might be configuring a mirroring port for capturing all Internet traffic, assuming people know what they do, between the WAN device (like cable modem, fiber termination boxes [FTP], optical termination boxes [OTP], bridged DSL modem, or bridged Starlink boxes) - if this can't be avoided, community members are suggesting to deploy alternate switches supporting management VLANs, or at least deploy static LAN IP addresses. Either way, it's not a usual, standard installation. That's why no bold warning is required.
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