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Forum Discussion
GS108E-v3 DHCP VLAN
I recently purchased this switch and was surprised to learn that when in DHCP client mode, it will pull an address from any device on any VLAN. I would have expected it to only work on VLAN1 or al...
Regarding the gateway question, I know why you would need one for a fully managed switch as it would have some sort of features to "call out" ie heart beating / emailing / monitoring but this switch has no such features exposed in the GUI where it needs a gateway.
As for the case of why you would have more than one dhcp server, there are actually two:
1. If I want a guest network, wireless for example, bridged to the LAN, segregated by VLAN, I'll likely have a different dhcp subnet as well. If the dhcp server is on another device and VLANs are used to determine which subnet and address to issue, it is possible for the switch to get an address from either and not be on the expected VLAN. (essentially being on the wireless VLAN)
2. Some ISPs allow multiple public IP addresses. To have multiple devices get them, you would have the modem and those devices on a separate VLAN and the devices would have their own WAN links. Since the switch pulls DHCP from any VLAN, if the modem serves an IP faster on VLAN 2 than the server on VLAN 1, your switch and its admin capabilities are now on the WAN instead of the expected LAN.
The case for using dhcp instead of a static IP would be for easy management. If for some reason the switch IP needs to change, I can still access it via its DNS name, which in my case is static in the sense that the dhcp server has a static mapping to the switch's mac address.
In a strict best practice sense, you are right, stick to static, but I wanted to highlight this because its a pretty big deal for a device, a business device no less, one of whose biggest features is to segregate traffic, does not bother doing that for its own traffic.
As for the case of why you would have more than one dhcp server, there are actually two:
1. If I want a guest network, wireless for example, bridged to the LAN, segregated by VLAN, I'll likely have a different dhcp subnet as well. If the dhcp server is on another device and VLANs are used to determine which subnet and address to issue, it is possible for the switch to get an address from either and not be on the expected VLAN. (essentially being on the wireless VLAN)
2. Some ISPs allow multiple public IP addresses. To have multiple devices get them, you would have the modem and those devices on a separate VLAN and the devices would have their own WAN links. Since the switch pulls DHCP from any VLAN, if the modem serves an IP faster on VLAN 2 than the server on VLAN 1, your switch and its admin capabilities are now on the WAN instead of the expected LAN.
The case for using dhcp instead of a static IP would be for easy management. If for some reason the switch IP needs to change, I can still access it via its DNS name, which in my case is static in the sense that the dhcp server has a static mapping to the switch's mac address.
In a strict best practice sense, you are right, stick to static, but I wanted to highlight this because its a pretty big deal for a device, a business device no less, one of whose biggest features is to segregate traffic, does not bother doing that for its own traffic.
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