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pass-through DHCP + a mixture of public & private IPs

Discussion in 'General Discussion' started by Anonymous, Nov 11, 2004.

  1. Anonymous

    Anonymous Guest

    ? Can I do pass-through DHCP with the Linksys WRT54G ?

    preference 2:
    My DHCP server is Comcast, from whom I can get up to 7 public IP Addresses. The WRT54G would retrieve the public IPs and assign them to the computers, either directly or wirelessly connected. Those computers will update DynDNS.org

    preference 1:
    This would include preference 2 plus would allow for a list of machines to receive the public IP addresses. All other machines would receive Private IP addresses by the DHCP functions of the WRT54G.

    Thanks in advance for the advice -
  2. Lazybones

    Lazybones Network Guru Member

    You would have to staticly assighn your local computers and leave the ones that you want to have comcast IPs on DHCP mode.

    I am not sure how this would impact NAT, I don't think you would be able to have the router also run NAT because it would need its own Comcast IP.

    What would work and would be much easier to setup would be this configuration.
    Comcast Modem ---> Hub/Switch---->WRT54G--->Local NAT Computers
                                 ---->Comcast Computer 1
                                 ---->Comcast Computer 2
    This would of course put your computers with comcast IPs on the WAN side of the router, making them contact able by your local NAT computers as if they where any other computer on the internet. You would not be able to use windows sharing (without problems) between computers with a NAT ip addres and the ones with Comcast IP addresses.

    If you had Static Comcast IPs it would be a different story, then you could assign those throgh the router and have them on the same side as other local computers.

    This is just one way you could set things up.. Why do you want these computers to have thier own Comcast IP?
  3. Garitaar

    Garitaar Network Guru Member

    Thank you, LB

    Your well-done sketch is exactly what I do now, except that the WiFi box is another vendor, a Netgear, which I regret I want to replace.

    Comcast routers are at each fiber-hub (not to be confused with an IP-hub). Suburbs with lots of users may have multiple subnets, and the uplink speed of 300kb/S becomes the bottleneck in tranfering files between the WiFi (private IP) 'puters and the 'puters that have public IPs.

    I have considered installing a dataswitch with OSPF in place of the existing "broadcast mode" dataswitch. If I could find an OSPF intelligent dataswitch for under $1k I would give that a try.

    I travel for my work and therefore require some public IPs. At the moment I am in Africa where they pay over $1,200 US per month for 128 kb/S of internet packet transport. These good people nearly fell off their chairs when I told them I had 300k up and 4M down and 7 public IPs for under $100 per month from Comcast. I almost feel guilty for being bothered by the 300 k bottleneck. Have we got it good in the USA, or what ?!?!?

  4. Lazybones

    Lazybones Network Guru Member

    If you are using a switch to connect your comcast, Public computers and your Router, the router should be rout the traffic without going out and through comcasts limits. The only limiter should be the routers wan port. But I guess that depends on the the the switch..

    You described a "broadcast mode" switch, wouldn't that be a hub? As switch normally remembers the mac of every computer on each port then directs traffic only to those ports when needed.

    I probably shouldn't mention that here in Canada I have a 5Mbit Down 1 Mbit up connection. And its fixed bandwidth not shared like older cable systems. I also only pay about $50 CAN for it.
  5. Guyfromhe

    Guyfromhe Network Guru Member

    if the machines are switched on the same subnet they shouldn't be going over the internet, if you're running win2k or better you can put an internal ip on your nic as well as your external ip to stop the files from being sent out to comcast and back... other thing you could do is setup a computer running freebsd or similar and you could route the 7 ips to the machines the need them and nat what you want and juse use the WRT as an access point, thats what i'm doing right now and it works great :) btw I have the same pkg as you the 5/1 for $50 CDN :p
  6. Lazybones

    Lazybones Network Guru Member

    Don't the 7 IPs need to be static for that to work? the WRT already runs linux so if its just a matter of iptables rules you should be able to do almost the same thing as your freebsd system.

    Again complex routing configuration is not my specialty.

    On Shaw Extreem then I take it? I am very impressed with the new DOCSIS network. I had Shaw years ago, then Telus ADSL now I am back to Shaw. I must say its the best high speed service I have used.
  7. Guyfromhe

    Guyfromhe Network Guru Member

    The ips don't nesicairily have to be static though that makes it easier...I don't know if this "mini" version of linux has the appropriate packet re-routing capabilities built into it, and even then it would be a nightmare to try to do it on a router. You could probably pull it off with a linux box (i've never tried) i've done it before with bsd and I know it's relatively easy with that...

    Shaw extreme works great :) I tried MTS adsl many years ago and I tried it at someones house recently, shaw 0wns them.
  8. Garitaar

    Garitaar Network Guru Member

    Let's simplify the question and take it is steps.

    Can the LinkSys be made to allos Pass-through DHCP? In this configuration, the DHCP server is on the WAN side and the LinkSys-LAN-Workstations request an IP. Rather than the LinkSys providing the LAN element a private IP, the IP request passes through the LinkSys and into the WAN, where another DHCP server can reply.

    Does any of the software discussed here provide that?

  9. TazUk

    TazUk Network Guru Member

    If the Linksys is configured as a router rather than as a gateway, which is the default setting, then DHCP requests should pass through. How useful that will be I don't know as the addresses will be from the WAN side and therefore a different range to the LAN side where the PC's are connected.
  10. Guyfromhe

    Guyfromhe Network Guru Member

    you could also bridge the wan port to the lan port
  11. jmbach

    jmbach Network Guru Member

    This is a similar setup I would like to do. In my case the setup would be a cable modem attached to the WAN side of a SonicWall Router which is my DHCP server and hardware VPN to an office. The LAN side of the SonicWall would connect to the WAN side of the WRT54GS which would passthrough all the DHCP requests to the connected devices on the LAN/WLAN side of the WRT54GS. The WRT54GS would not do any NAT on the network since the WRT54GS would have the same IP address subnet that the Sonic wall LAN side and all other connected devices would have.

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