DHCP Reservation - same MAC, two networks
Hi,
I have an ER605v2 and Omada (software) controller running 5.9
I'm trying to setup DHCP reservations for a single client that is connected to two VLANs on the same port - and hence same MAC address. I'd like to reserve an address for each VLAN, the controller UI does not allow me to do this - it claims there is a conflict in MAC address reservation even when I try to add the two reservations on their respective (different) VLAN networks.
This seems to be a bug - there's no reason a single MAC address cannot have a reserved IP address on each network.
Is this a known issue? Any workarounds?
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Hi @axorb
Thanks for posting in our business forum.
First, what you said is not possible. You can set two VLANs on a single port but the device will only get a single IP address at a time unless you modify the port setting and its PVID. So, a device will only get the IP address from the untagged VLAN. There is only one IP address.
The Controller did not allow this then it is blocking such a config from the system level. MAC address is the only identifier in a network in layer 2. MAC address should not show twice when it relates to the IP addresses. From the OSI, you can do this manually by changing the IP address. But our system is not gonna allow this. It's counter-intuitive in networking.
This is not a bug. This is against the use. We limit this because we don't want this to cause trouble when you use your networking and change this accidentally. Some open-source stuff may not limit this but you are on your own with your network.
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@Clive_A the client device is a Linux machine that is able to connect to a single port as a trunk port. It can define 2 virtual interfaces on the single port and tag vlan packets as needed. This means the client is perfectly capable of communicating with the network on 2 vlans from a single port. Given the DHCP request on each vlan will be appropriately tagged, the DHCP server should be able to differentiate which network the request is from and thus which address to assign.
I have this working on my existing non-omada router just fine.
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axorb wrote
@Clive_A the client device is a Linux machine that is able to connect to a single port as a trunk port. It can define 2 virtual interfaces on the single port and tag vlan packets as needed. This means the client is perfectly capable of communicating with the network on 2 vlans from a single port. Given the DHCP request on each vlan will be appropriately tagged, the DHCP server should be able to differentiate which network the request is from and thus which address to assign.
I have this working on my existing non-omada router just fine.
We don't support this. And you look for a workaround, then you should consider setting a static IP to your Linux.
If it is a Linux and can use two VLAN tagged traffic, then you've trunk-ed it and it is more like a switch.
Like I said, it's counter-intuitive to our system.
VLAN is the logical separation while the MAC address is the only identifier. MAC and IP have a direct relation because the MAC address determines the IP address.
But VLAN and MAC address, are both at layer 2, VLAN is tag/untag is determined by the preset you have for the device.
And if it has two virtual interfaces, you should have different MAC addresses to them. Then you should set the MAC addresses of different interfaces to IPs.
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