Centralised DHCP

[stroighne]

Hi,

Deploying MX devices into existing MPLS routable /24 subnet. The issue I have is that clients are not picking up DHCP IP addresses whilst connected to the MX.  They pick up the DHCP IP address as expected when the MX is removed from the equation. 

I am relaying to the relevant DHCP server. 

I've been told conflicting responses from two Meraki System Engineers that I need a unique subnet between the MX and MPLS router (say a /30) ...is this true, and if so....why?

Many Thanks

[TylerJ]

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@stroighne1 wrote:

Hi,

Deploying MX devices into existing MPLS routable /24 subnet. The issue I have is that clients are not picking up DHCP IP addresses whilst connected to the MX.  They pick up the DHCP IP address as expected when the MX is removed from the equation. 

I am relaying to the relevant DHCP server. 

I've been told conflicting responses from two Meraki System Engineers that I need a unique subnet between the MX and MPLS router (say a /30) ...is this true, and if so....why?

Many Thanks

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Hi Stroighne1,

I would need a little more detail to help here to understand where the client needing DHCP is located and the topology in between. I don't believe a dedicated /30 should be required. 

This sounds like something our Support team can quickly solve - so if you have a few minutes to test this and troubleshoot - I'd give them a call and work through the issue. 

Hope this helps!

Best,
-Tyler J

[Jollywombat]

What does a packet capture say when doing one while issuing a dhcp request?

[stroighne]

Thanks Tyler,

We have a MPLS network. DHCP server is located in 1 of our DC's which is connected to the MPLS network via resilient 100Mb circuits. 

At one of our 450 remote sites (all connected via MPLS with centalised breakout) I have deployed an MX65. 

MPLS provided router peers with the PE via a /32 loopback interface, they then advertise a /24 via BGP for us to use on the LAN. 

When I physically connect the MX65 via internet port 1 to a LAN port on the Cisco router it indeed picks up an IP address from our DHCP server. The issue I have is, that when I configure one of the Meraki LAN ports to be in the same vlan as the routable /24 the devices do not pick up a DHCP reply. Packet capture can see the request hitting the DHCP server and the response coming back, but it hits the MX and then goes nowhere.

I'm aware I can use the MX to manage DHCP, however it's not the way we want to go (for now at least). 

As an example I have the MX WAN IP as .209 with the LAN IP as .210 with the default gateway on the Cisco router as .220.

| have spoken to the support team, and they advise that there needs to be a different subnet between the MX and the Cisco router. 

I was just curious as to why this is the case, if indeed it is true. 

Many Thanks