DHCP Server with 2 VLANs and 2 Routers

redgunnerredgunner Posts: 42Member ■■□□□□□□□□
Hello,I have 2 VLANs as you can see with a DHCP Server, I have succesfully got it working on the left hand side but I am trying to understand the theory of the right hand side.I have set the default gateways as the same as the left? (is that do-able?) whats the best approach to this? (I am using EIGRP as my routing protocol)


  • OctalDumpOctalDump Posts: 1,722Member
    So the VLANs on each side are separated by routers. Unless you have a VPN connecting those, you would put them on different subnets. So VLAN 2 on the left would be a different network (subnet) to VLAN 2 on the right. After that it is fairly straight forward to replicate what's on the left to what's on the right using different addresses.

    If you do have a VPN, then you'd just make the end points of the VPN a DHCP relay.
    2017 Goals - Something Cisco, Something Linux, Agile PM
  • rolando3321rolando3321 Posts: 36Member ■■□□□□□□□□
    R1 currently has vlan2 and vlan3 with the networks and -- (I'm going to assume they are /24)

    (I'm going to look at a situation where we act as if we can advertise the same network for router 3)

    You use EIGRP to tell the other routers that R1 has networks and connected to it. You then set up R3 with networks and

    Then for the sake of random IPs:

    on the left side (connected to R1)
    default gateway for vlan2
    ip on clients you use, .11, .12, .13
    default gateway for vlan3
    then you use, 11, 12, 13

    Then on R3
    vlan2 default gateway
    clients you use, .111, .112

    vlan3 default gateway
    clients you use, .111, .112

    So in this little mock up we have no duplicate ip addresses. The issue is that R1 and R3 are advertising the same network, so this doesn't work.

    You may already know all of this and I apologize if that is the case.

    As Octal mentioned, if you just want to make it work then use different networks. For example, you could use and for your vlans on the right. Then you make your IP helper address on R3 like you did on the other side and make dhcp pools for these networks on the server.
    If you want vlan2 on the right and vlan2 on the left to act if they are on the same subnet - that is where the vpn comes into play (I think, someone please correct me if I'm wrong)
Sign In or Register to comment.