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I have an environment with two subnets 192.168.1.x/24 and 192.168.2.x/24

Each subnet/network has a Cisco RV082 router as the gateway and a domain controller in each environment that also has a DHCP server on it.

The Cisco RV082 routers are connected to each other via a LAN extension setup by the ISP so both offices are connected via a fibre link. So think of it as a switch between the two and they are directly connected to each other.

Currently what happens is when a client from either network sends a DHCP broadcast both DHCP servers in both networks respond to the request and sometimes a client that's supposed to be assigned a 192.168.1.x address gets a 192.168.2.x address and vice versa.

How do I stop the DHCP servers from communicating past their gateway into the other network? I have looked into the Cisco RV082 settings and I cannot find a setting that will accomplish this. DHCP relay wouldn't work in this scenario.

qroberts
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    You mean your router send broadcast from both side on the wan link ? It's a setup error as you will kill your wan link if someone broadcast too much – yagmoth555 Jun 08 '16 at 13:35
  • Have you looked at [dhcp snooping](http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_44_se/configuration/guide/scg/swdhcp82.html#wp1070843) ? – NickW Jun 08 '16 at 13:36
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    This... doesn't make much sense. You are talking about two "routers", but if they behave like you are saying, they are effectively acting as bridges and connecting your networks at layer 2, not at layer 3 like they should. – Massimo Jun 08 '16 at 13:43
  • @yagmoth555 Both routers are connected to each other on LAN port 8 on each router. There are 2 WAN ports on each router, WAN1 is connected to the ISP and serves an internet connection, WAN2 isn't being used. Should I use WAN2 instead of LAN8? I can see how this would make more sense. I thought there would be more granularity/configuration options for each port. – qroberts Jun 08 '16 at 13:44
  • Would I assign a static IP for WAN2 on each router in a new subnet such as 192.168.3.x/31? – qroberts Jun 08 '16 at 13:49
  • You mix two thing, the config your ISP did is a lan extender, and you talk like you have two different subnet on each side, like you would have a VPN tunnel. – yagmoth555 Jun 08 '16 at 13:59
  • Before the LAN extension was put into place both of those Cisco RV082 routers were connected to each other via VPN over the internet. I would like to keep two different subnets, one for each office if possible while having a DHCP server locally in each network. – qroberts Jun 08 '16 at 14:43
  • A LAN extension would imply that they provided you a method to extend the same subnet, where as what you actually wanted was a link to bridge your 2 subnets (a site-to-site connection). I think you will need to speak to your provider and have them replace the connection with a site to site, as you are currently bridging subnets. It's like, effectively, they've just plugged a network cable between both switch stacks. If you did that between two racks hosting different subnets, this is what would happen. You can be sure of this if a client in the .1.0 subnet can route out if assigned a .2.0 IP. – Alex Berry Jun 08 '16 at 14:44
  • Can I use [Advanced Routing](http://sbkb.cisco.com/CiscoSB/GetArticle.aspx?docid=0eed5b00c5be40e09722ac0fe4eb3cb0_Advanced_Routing__Static_Routing_Configuration.xml) to route the packets to the other subnet instead? Looking at other options before contacting the provider. – qroberts Jul 14 '16 at 17:04

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Cisco RV082 doesn't support DHCP snooping, Thinking of adding a firewall like PFsense to isolate the other network or authorized DHCP in Active Directory.

Demz
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