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Thread: Setting up static IPs using a Comcast Business Gateway

  1. #1

    Setting up static IPs using a Comcast Business Gateway

    I have a 5 static IP (public/external IPs) package from Comcast Business Services and a Comcast Business IP Gateway. Now I would like to connect my router to the gateway and use the gateway's DHCP to dynamically assign it an internal address which is as simple as connecting the router to one of the gateway's ports as the gateway's internal DHCP server is automatically enabled. There is a range that you can specify and all the devices connected to the gateway are assigned a random IP (for a specified lease time) from that range. Now however, I have 2 servers that I want to assign static IPs. Both servers are directly connected to the gateway. I tried directly assigning a static ip each to the servers (I have all the information - IP address, subnet mask, default gateway, primary and secondary DNS) but the servers are unable to access the internet. I understand this is because they are all behind the gateway. The gateway is dynamically assigning internal IPS via DHCP to both servers like it is to the router above. These are Windows Server 2008 machines. Can someone please guide me in the right direction here. I am fairly new to networking of this nature. I want separate static ips for each of my 2 servers. Again these are external IP addresses, I have 5 of them that I purchased from my ISP.

    Thanks a ton in advance.

  2. #2
    Moderator YeOldeStonecat's Avatar
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    The SMC appliance (gateway) that Comcast ships with their static Biz accounts, by default, will utilize an IP on its WAN interface, and provide NAT/firewalling for devices plugged into it that have their TCP set to obtain auto...it will hand out IPs something like 10.1.10.100...or something like that. So it acts like any home grade router in that respect.

    When you want to use your own router ...and put one of your static IPs to your own router....you simply plug in that static IP/subnet/gateway/DNS into the WAN interface of your own router, ....and plug your routers WAN interface into one of those 4 ports in the back of the SMC gateway.

    Or if you want to plug in just your bare server...with that server on that IP address...you could do that, but I highly...highly recommend you don't plug a server right onto a public IP address, stick it behind a good router/firewall with NAT, and have only the bare minimum ports open/forwarded necessary to make available whatever it is that this server does.

    If you're running 2x servers...most decent firewall/routers will support multiple IPs on the external interface.

    That particular IP (range) address/subnet/default gateway/dns is on the sheet of paper that you got from Comcast when you had your biz account setup/installed.

    The last thing is to log into the SMC device, and shut off it's firewall. I forget the LAN IP again..something like 10.1.10.1...(just set your IP to obtain auto, plug into it..do an IP config /all)....
    username and password are something like cusadmin and highspeed.
    Look around, there's a "disable firewall" checkbox around there.
    MORNING WOOD Lumber Company
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  3. #3

    Comcast SMC Gateway

    Thanks a ton for replying. That was really precise. I was hoping someone who had experienced Comcast's infrastructure would be able to help me out. Yes the gateway by default is accessible at 10.1.10.1. The SMC device (Gateway) then dynamically assigns all the devices connected to it, DHCP generated IPs between 10.1.10.1 and 10.1.10.99.

    Now as you said, If i want to assign my router a static IP you said "you simply plug in that static IP/subnet/gateway/DNS into the WAN interface of your own router, ....and plug your routers WAN interface into one of those 4 ports in the back of the SMC gateway". I'm a noob to this and I apologize for my lack of networking knowledge. What exactly should I plug in to my router in the first part of your sentence? I understand that after that I then have to connect my router to one of the 4 ports behind my SMC gateway. I am guessing that you meant that I connect whichever server I want to my router when you said "you simply plug in that static IP/subnet/gateway/DNS into the WAN interface of your own router". How would the router itself be assigned one of those 5 static IPs ? Or am I getting my objective confused here. Should the router be on one of those 5 static IPs that I have or should I just permanently assign it with the SMC gateway's already assigned DHCP IP (e.g. 10.1.10.123) that was delegated to my router when I connected it to the gateway ?

    Do you mean connect my servers to my router which is connected to the gateway and assign those servers static IPs using my router ? I understand the security risk in connecting my server directly to the SMC gateway, and will not really be doing that. But if I wanted to how do i assign one of the 5 static IPs i got from Comcast to my server when it is directly connected to the gateway ? I tried doing it by manually assigning the static IP info in Network Connections in Windows Server 2008 but that didn't work because the server is behind a gateway and is not directly connected to the public network. I just lost network connectivity.

    Thanks a ton for your patience

  4. #4
    Moderator YeOldeStonecat's Avatar
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    It should have worked if you plugged in the information that Comcast gave you for your static IP.

    They should give you your range of IP addresses..and highlight the "first usable IP".

    You'd take that first usable IP in the range they gave you, and enter it into your servers network properties...TCP/IP...(IP4)....
    The IP address
    The subnet mask they gave you
    The default/remote gateway they have you
    And if your server is a stand alone server in workgroup mode...you'd enter the DNS servers that they gave you.

    The gateway they give you to use is usually the first or last number in the IP range that they put aside for you.

    Now, sticking a Windows server out on a public IP address...even for just 1 minute...it risky...very risky. Within a matter of seconds it'll start having scripts and bots and trojans and other exploits banging the doors down on it. There is a lot of work that has to be done on a Window server to prepare it for sitting on a public IP address.

    Best thing to do (and what I do) is take your own router or firewall...and plug in that information above you got from Comcast...into its WAN interface. When I say WAN interface..that means the external part of your router, the internet interface, the outside connection. Commonly for home broadband users, this is left to "obtain auto/dhcp" from your ISP (common for cable), or...PPPoE (common for DSL), where you enter the username/password.

    But with static IP setup with Comcast....you set the selection for your WAN interface to Static IP...which opens up all those fields to enter the assigned IP address, subnet, gateway, and DNS.

    Once you enter that information into the WAN interface of your own router, you uplink that WAN/Internet port of the router, to one of the LAN ports of the SMC. Now, take a computer and plug it into one of the LAN ports of your own router...with TCP set to obtain auto...that PC will pull an IP from your own router..something like 192.168.1.100. If you're successfully connected to the internet, and if you go to www.whatismyip.com you should see it report the public IP address that you plugged into the WAN interface of your own router.

    So what you do now is put your servers behind your own router, plugged into the LAN ports...assign your servers internal static IP addresses (or give them reservations in your own routers DHCP service)....something like 192.168.1.10 for example. And now, you open/forward the ports on your own router that are necessary to make the services you wish to be available...available out on the internet, forwarded to the internal LAN IP of your servers.

    What will these servers be doing?
    MORNING WOOD Lumber Company
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  5. #5
    Hi,

    I had initially done what you told me to before I actually posted here. I took one of the 5 Ips from the range Comcast gave me and fed it in to my router's (which was already connected to the SMC gateway) WAN interface using the static IP setting on the router. At the time of feeding in that information it also asked me for a MAC address, I gave it the MAC address of my computer and set it. Then when I browsed to whatismyip.com it showed me the correct static IP, the one that I just set. I am not sure however if I should have set my router's MAC address at the time of setting up this config or whether my computer's MAC address was ok. I think the latter is wrong, this probably means that my machine is sitting buck naked on that public IP.

    Now, I can try changing MAC address to my router's MAC address instead. If I do this I am guessing that my computer or anything else connected to the router would be auto assigned a DHCP generated address by my router. However, if the router itself is now sitting on the public IP, would I still be able to access my router's administration page on the same internal IP (e.g. 192.168.0.1).

    Also, I thought that my SMC gateway should probably be sitting on one of the 5 IPs Comcast gave me too, but apparently it isn't. When i checked the status of the SMC gateway it says WAN DHCP: 67.x.x.34. And when my computer is directly connected to the gateway (instead of my router) this is the IP whatismyip.com shows me. This address is not in the 5 IP range Comcast assigned to me.

    I am currently experimenting with infrastructure with a colleague of mine (we are software developers working on a personal project that we want to turn commercial) and haven't defined our server responsibilities yet. We were thinking of setting up our own DNS. And then hooking up a Web Server and an Application Server.

    Thanks.

  6. #6
    Moderator YeOldeStonecat's Avatar
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    No fiddling of MAC addresses should be required. The only thing you might do with your computers MAC address is enter it into your own routers DHCP service reservation section.

    Your routers WAN interface is what gets the static public IP.
    Your "server" would be behind your router (inside really)..on the protected private side of it. Say your router has a LAN IP of 192.168.0.1, and your server has 192.168.0.10, yes you can still access your routers web admin at 192.168.0.1 from the server.

    If you want to run a web server you'd open/forward port 80 on your own routers port forwarding section, to the LAN IP of the server, 192.168.0.10 for example.

    So...traffic coming from the internet, seeking your static public IP address of 67.blah.blah.blah..that traffic hits your own routers WAN interface..and the port forwarding forwards to that to your servers LAN IP of 192.168.0.10.
    MORNING WOOD Lumber Company
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  7. #7
    If you look at pg. 21 of this document, you will see the static IP setup screen of my router (Dlink DIR 655).

    http://www.scribd.com/doc/2090673/DIR655-manual-11.

    There if you notice, I specify one of the static IPs from the range given to me by Comcast and fill out all the necessary info. At the bottom it asks me for a MAC address. I can leave it to its default setting. But is that the right page that I am using to configure my static IP ? Also, any idea why my SMC Gateway is not on one of the IPs in the range given to me by Comcast. the 67.x.x.x address is the WAN DHCP address. Wouldn't that change ?

    Also, pg. 8 in the following document is how my SMC Gateway's settings look like.

    http://worknetkc.st.comcastsupport.c...Raw%20Document

    Thanks again for all your help.

  8. #8
    Moderator YeOldeStonecat's Avatar
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    Quote Originally Posted by cranialsurge View Post
    If you look at pg. 21 of this document, you will see the static IP setup screen of my router (Dlink DIR 655).

    http://www.scribd.com/doc/2090673/DIR655-manual-11.

    There if you notice, I specify one of the static IPs from the range given to me by Comcast and fill out all the necessary info. At the bottom it asks me for a MAC address. I can leave it to its default setting.
    Ahh...yes, routers have the option to "spoof a MAC address"....that is nothing you have to deal with. Some ISPs used to reserve an IP address for you based on the MAC address. If you change router router for example (say one blows up)...a new router would have a new MAC address, since all network devices have a unique MAC address..much like the VIN on your car. You have the option of entering your old MAC so you get your original IP back that the ISP would reserve for you. Versus...calling the ISP to have them bind your original IP address to your new MAC address. Thus...MAC spoofing. Regardless, you can disregard that section and leave it default.
    MORNING WOOD Lumber Company
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  9. #9
    Moderator YeOldeStonecat's Avatar
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    Quote Originally Posted by cranialsurge View Post
    Also, any idea why my SMC Gateway is not on one of the IPs in the range given to me by Comcast. the 67.x.x.x address is the WAN DHCP address. Wouldn't that change ?.
    Depending on the setup of the local Comcast branch near you, and how they have their DHCP and reservations setup...if your SMCs own address is different...also nothing to worry about. The ones I setup are usually right next to the IP block up where I am, but if yours is of quite a different range...don't worry about it, the 5x IPs that they reserved for you is what counts.
    MORNING WOOD Lumber Company
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  10. #10
    Moderator YeOldeStonecat's Avatar
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    Quote Originally Posted by cranialsurge View Post
    But is that the right page that I am using to configure my static IP ?
    Pages 21-23....yes, that's it.
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  11. #11
    Moderator YeOldeStonecat's Avatar
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    Quote Originally Posted by cranialsurge View Post
    ge ?

    Also, pg. 8 in the following document is how my SMC Gateway's settings look like.

    http://worknetkc.st.comcastsupport.c...Raw%20Document
    Chapter 3, page 10....checkbox for "Disable firewall for true static IP subnet only"....you will want to hit that, by default the firewall is running which will block port 80 and other stuff.
    MORNING WOOD Lumber Company
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  12. #12
    Ooh, nice ! Thanks. Now, so do you think that the fact that my gateway is not on any of the IPs in the range Comcast assigned to me is a problem ? Also I am wondering what the WAN DHCP thing is that is the IP also reported by www.whatismyip.com. 67.x.x.x When I add my router to the gateway, it gets assigned an internal IP ... 10.1.10.x However if I assign the router a static IP like you said on that screen (dis-regarding the MAC address), would 10.1.10.x still hold ? I mean wouldn't the public IP that my customers would have to hit still be the Gateway's WAN DHCP ... the 67.x.x.x even though the router will now be on a public IP 123.x.x.x with all my servers inside the router?

  13. #13
    Moderator YeOldeStonecat's Avatar
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    Your SMC will, by default, get some public IP address on its WAN interface by Comcast. You can disregard what this IP address is...it's just an IP address to get it online with Comcasts network.

    The device will "IP Map" your assigned 5x static IP addresses...sort of just act like a conduit. It's your devices with your manually entered static IP addresses that count.

    So if the SMC gets some 67.xxx.xxx.xxx address, and the 5x static IP addresses that you are assigned from Comcast are something like 76.xxx.xxx.xxx., all you need to do is assign your devices those 76.xxx.xxx.xxx addresses. When you go online, and hit whatismyip.com, it should report a 76.xxx.xxx.xxx address to you. The fact that the SMC has another 67.xxx.xxx.xxx address doesn't matter....you're really just funneling through the SMC. That IP it gets, the 67, is just for them to get to it, manage it, for it to get online with their bandwidth.

    Devices that you will plug into the back of your own router(s) will also get the correct 76. address when they go to whatismyip.com
    MORNING WOOD Lumber Company
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  14. #14
    Alright, thanks a million for everything. So just to summarize everything, this is what I am going to do:

    1.Permanently assign one of the DHCP generated internal IPs of the SMC gateway (e.g. 10.1.10.109) to my router that is connected to the gateway

    2. Take one of the 5 IPs and assign it to the router dis-regarding the MAC address field as we talked about earlier
    (e.g. 123.345.678.901)
    3. Connect one of my servers to the router and have it permanently reside on a specified internal IP (e.g 192.168.0.145)

    4. Now when I access the network from my server www.whatismyip.com should show 123.345.678.901 right ?

    Also, I am now wondering what I should do with the other 4 IPs that I got.

  15. #15
    Moderator YeOldeStonecat's Avatar
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    Scratch #1.....no need to assign anything 10.1.10.xxx.

    WAN/Internet port of your own router is plugged into 1 of the 4 LAN ports on the back of the SMC.

    Steps 2, 3, and 4 seem correct.

    Remaining question about the other 4x IPs? You can do a few things with those, depending on your needs. You can plug in a few more routers in the other ports of the SMC...and do the same setup..using those other static IPs.

    Some routers allow mapping of multiple public IPs to them.

    What is the make/model of your own router?

    Not to skip out on you...but I have to log off for the night...wife calling me to to do stuff.

    I'll be back online tomorrow morning before I do travel to a few onsites....and on/off throughout the day. Dunno your timeframe for this....but glad to help as much as I can.

    ---out for the night.
    MORNING WOOD Lumber Company
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  16. #16
    In #1, the router is already connected to port #1 of the 4 ports behind my SMC gateway. But the SMC gateway automatically assigns internal IPs within a specified range to all devices connected to it (internal DHCP server), so the router gets an IP assigned, (e.g. 10.1.10.109). But after I assign one of the 5 external IPs to the router (e.g. 123.345.678.901) it will still appear as 10.1.10.109 to the gateway even though any computer browsing the internet connected to that router will show up as 123.345.678.901 on www.whatismyip.com. So I thought I might have to make sure that the gateway doesn't change the router's internal IP from 10.1.10.109 to something else as the SMC gateway implements an internal DHCP server. So with step #1 I meant that I would make sure that the lease on 10.1.10.109 was set to never expire. Is that step not required ?

    My router is a DLink DIR 655. http://www.dlink.com/products/?pid=530

    Thanks so much for all your time and patience. I couldn't have asked for more. I don't think I've ever come across someone as helpful as you on a forum before. Good night and again, I really appreciate it.

  17. #17
    Moderator YeOldeStonecat's Avatar
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    Correct...worrying about the SMC running DHCP, and the static IP on the WAN interface of your router...no need to worry about it.

    Any device you plug in the back of the SMC, with TCP set to obtain auto, will get a 10.1.10.xxx address from the SMC, and appear to come from the SMCs 67. address.

    Any device you plug into the back of the SMC with a proper static IP address like 123....will not ask for an IP address from a DHCP service, so the SMCs DHCP service near hears that request, and never hands out an IP.

    I spaced out in asking what kind of router you have, can't believe I asked it again after even reading that screenshot of the manual and you already mentioned it. Doh!
    MORNING WOOD Lumber Company
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  18. #18
    Heya there,

    So guess what :|. I was so desperate to get things working and nothing I tried worked so I resorted to the forum, found an awesome guide in you and went back home last night to try things out. Worked for about 4-5 hours trying all sorts of attempts to no avail. Finally I resorted to calling Comcast tech support. The twits had assigned the wrong Static IP block to me !!! I mean seriously people !! "Business Class" it seems. And I wonder why everything that we talked about wasn't working. Thank you so much once again for your time and patience with this entire ordeal of mine. You've been awesome.

  19. #19
    Moderator YeOldeStonecat's Avatar
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    Ahh....glad they got it sorted out. On a side note, Comcasts Biz support has been one of the best I've experienced out of many ISPs...and I deal with a lot of ISPs on a regular basis.

    Document all the settings you're doing very well. If a router goes up in smoke, you'll want to get a replacement and enter all those settings again as they are.
    MORNING WOOD Lumber Company
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  20. #20
    Hey there. Yup Comcast's Customer Support was pretty prompt in handling my case. So I have the following setup now.

    1. My router is connected to the SMC Gateway and has a public IP assigned to it
    2. My Web Server is connected to the router and it has an internal IP (NAT)
    3. I have allowed access to the Web Server by port forwarding port 80 requests on my router to the web server (using the internally assigned permanently leased DHCP generated IP address). In addition to this I had to configure port forwarding on the SMC gateway (True Static IP Management) to forward port 80 requests to the external static IP that my router is at. Without doing this even though the router was configured to pass all http (port 80) requests to the web server connected to it, it was not doing so, the gateway had to be configured too.

    The last step poses another question for me, in this case how would I be able to have an additional Web Server serving http requests ? Port 80 on the SMC gateway is already pointing to the router.

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