How to make RVS4000 give DHCP clients a different IP address as default gateway

Unanswered Question
Apr 28th, 2010
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Hello folks


My name is Vaughan, and this is my first time on this discussion site.


I have been having a problem connecting a Vodafone femtocell into our company nework, which is currently set up like this.



  INTERNET

     |

     |

ISP Managed DSL

Modem Router

     |

     |

ISA Firewall

& Proxy Server

     |

     |

  LAN PCs


The device, which has no configurability at all, requires a DHCP assigned IP adress and creates its own VPN tunnel back to the Vodafone network. Initially I connected it into the LAN behind the ISA server and tried to configure the ISA serer, which required a web of ports to be forwarded. All attempts to get it to work there failed, and I concluded that limitations in the ISA server firewall meant that it would never work behind the firewall. In any case, Vodafone would not provide any support for the device in that configuration.


The solution seemed to be to insert it into the DMZ between the managed modem router and the ISA server. The managed router has only one LAN-side port and doesn't act as a DHCP server and I don't have access to it to change any of its configuration. I therefore bought a Cisco RVS4000 router to sit between it and the ISA server.


  INTERNET

     |

     |

ISP Managed DSL

Modem Router

        \

         \

           RVS4000

         /              \

        /                 \

ISA Firewall        Test PC (or femtocell)

& Proxy Server

     |

     |

  LAN PCs


I set the RVS4000 to router mode, gave it a new IP address in the DMZ subnet range, enabled DHCP in the same range and connected one each of the LAN-side ports to the managed router and the ISA server leaving the WAND side port unconnected.


Then, as a test, I connected a PC to a third LAN-side port. The PC was assigned an IP address by the RVS4000 as expected, but was unable to connect to the internet. Inspection of the connection settings showed that the RVS4000 had assigned its own IP address as the default gateway rather than that of the managed router. Manually setting the default gateway on the PC to the IP address of the modem router opened up the internet.


OK, but the femtocell device needs to have its connection settings assigned by the DHCP server - there is no access to any manual configuration. The trouble is, I can't figure out how to set the RVS4000 to assign the correct IP address (i.e the managed modem router's) as the default gateway.


Can any of you experts help me?


In Summary:


Simple question really, how can I get the RVS4000's DHCP server to assign another IP address other than its own as the default gateway to its DHCP clients?


Thanks for reading this, and in advance for any help you can offer.


Vaughan

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