sKy Broadband - Their Router + My Router

[EvilMunky]

Hey Folks,

So here is the situation. I am being connected this Thursday (apparently) for Sky BB on their max service. It is a new phone line in a property i have just bought. I currently have no BB at the house. I have 3 main computers and one laptop.
Currently all are connected via a netgear rangemax type router (not modem - i used it when i had cable at my old house). Three machines are hardwired into the router and the laptop is wireless. What i want to do is to use the Sky BB router that gets supplied (T&C say i have to use this - from my understanding) and connect that into the uplink of my netgear router. So basically my network stays the same with the addition of skys router for internet access.

Question is, would this work? Will NAT'ed stuff still work? Is there any potential issues with this? Networking isnt one of my strong points and havent tried this in the past so just wandered if it was possible, in theory i guess it kind of acts as a DMZ.

Thoughts and comments welcome, as long as they are not comments like "Why would you want to do this?"

[Re-Invented]

Shouldnt see a problem as long as DHCP is turned off on the sky modem else you will end up with both of them trying to assign IP addy's

Lee

[EvilMunky]

Thats pretty much what i thought.
Cheers

[roddines]

WARNING - All is not so simple - There are at least two main very different scenarios to choose from here and so far your seem to be just discussing and assuming one of them and as far as I can see the comment by Re-Invented (which you are agreeing with) is actually wrong (or at least miss informed and misleading):

To explain why properly is complex so bear with me...

Note: WAN Port = Internet Port

Scenario 1a. Whichever ADSL ISP (Sky) -> (WAN) SkyBB box (LAN) -> Ethernet cable -> (WAN) Netgear Router box (LAN) -> Your computers AND Netgear Wireless Access Point (LAN) -> Your laptop



In this scenario you have 2 x NAT (Network Address Translation) plus 2 x Firewalls occuring one on each box, both in series. The additonal LAN ports on the SKYBB box will not have any access to the LAN/WLAN ports on the existing Netgear box and are essentially isolated and useless to you.

As a side note: This effectively means that those spare LAN ports on the SkyBB box (assuming it has any) are in what is known as psuedo DMZ (De-Militarised Zone) in this scenario (i.e. they can't easilly see or be seen by the Netgear LAN). Which I doubt you have any use for. Typically these would be used for hosting an Email (SMTP), Web (HTTP) or external File (FTP) server for example. However if you do have a need for this then that would be an advantage to this scenario.

Scenario 1b. Whichever ADSL ISP (Sky) -> (WAN) ADLS Bridging (Passthrough) modem (ie Netgear DM111P) (LAN) -> Ethernet cable -> (WAN) Netgear Router box (LAN) -> Your computers AND Netgear Wireless Access Point (LAN) -> Your laptop



This is the best scenario as you have only 1 x NAT occuring (Network Address Translation) only the one on your existing Netgear Router box and you get to use it for Firewall/Security. That is because the dedicated modem is working in Bridging/Passthrough mode (which it has to be setup to do).

Scenario 2. Whichever ADSL ISP (Sky) -> (WAN) SkyBB box (LAN) -> Ethernet cable -> (LAN) Netgear Router box (LAN) (a)-> Your computers AND Netgear Wireless Access Point (LAN) (b)-> Your laptop (as well in this scenario you can use the extra LAN ports on the SkyBB box for your computers if need be.)



Only 1 NAT occuring here (on SkyBB Box) but you lose your existing Netgear box Firewall/Security settings/configuration. And you have dual DHCP and configurations issues.

Actually in Scenario 1(1a or 1b) the DHCP option can stay on, on the SkyBB modem/router box or a Netgear dedicated ADSL bridging modem. Further it is better if it does stay on too. This is because DHCP is never routed through the WAN port of your existing Netgear router into the LAN side (so your computers only ever see the DHCP from it and not the other box). This is all assuming that in this scenario (1a or 1b) you are plugging the WAN port of your existing Netgear box into a LAN port of the SkyBB box (and not using any other SkyBB wireless or LAN port connections). Which is the way I would do it if I was not going to buy a dedicated ADSL bridging modem.

That way all your firewall settings stay the same on your existing Netgear box. In this scenario (1a) the SkyBB box basically becomes a simple modem/router rather than a LAN switch/WLAN access point (assuming it has wireless....further if it does you will want disable it so as not to cause unneccassary interference). However they will both still use NAT and you will have two NAT devices in series which is never ideal. You will potentially also have two Firewalls in series and you should minimise or disable the firewall on the SkyBB box. I.E. it should not restrict anything that is allowed to pass by the existing Netgear box firewall. The easiest way to bypass the SkyBB box firewall is to setup its DMZ setting to be the same as the WAN port setting on the existing Netgear box. This may seem to be confusing and contradictory to ealrier comments about a pseudo DMZ on the remaining SkyBB ports (in this scenario 1a), but it is correctly stated.

The SkyBB box may have a bridging modem option...If it does, then use that option in this scenario (but I doubt that it does). Alternatively buy a proper ADSL bridging modem and use that with your exisitng Netgear box (scenario 1b). They are not expensve and the recommended Netgear one (i use it all the time) has great ADSL diagnostics gear onboard. This is the way I personaly would go. You can always drag out the SkyBB box and do a simple direct computer connection with it if you need Sky support for a bad line situation (assuming they will only support their modem).

You can get one (Netgear DM111P) here...

http://www.broadbandbuyer.co.uk/Shop...ProductID=3826

for under £30 inc VAT

In the second scenario (scenario 2).... If you plug the LAN side of the two devices into each other (assuming you use a cross over cable or one of the devices support auto crossover connections...I think the Netgear will do that automatically) then your existing Netgear box just becomes a Network Hub/Switch and Wireless Access Point. Then its NAT/Firewall and WAN port are never used. But you can use both sets of LAN ports for devices on both boxes.

The Netgear firewall/security will be bypassed and that feature will remain only on the SkyBB box (assuming it has any). If you do choose that scenario you would normally turn off the DHCP on the Netgear box as the SkyBB needs to be the default gateway so the connected PC's can find the internet. Thus by default its' DHCP will be the one issuing the correct DNS and Default Gateway settings to the computers.

You could alternatively turn off the DHCP on the SkyBB and manually adjust the DNS (to use the SkyBB box to resolve DNS or use the ISP DNS directly) and the Default Gateway settings (to point to those of the SkyBB box LAN port) on the existing Netgear box so thats its DHCP default gateway setting is OK too. But that means you would need manual settings that may change over time.

This scenario can be good because only one NAT (on the SkyBB box) remains between you and the internet. But you lose the best Internet firewall/security features of the exisitng Netgear box and your essentilaly turning it into a simple Wireless Access Point/LAN Switch.

Also the LAN IP setup of the two devices can technically be the same in the first scenario while they must be similar but not exactly the same in the second scenario (ie two different address on the same subnet works best). However I would make sure that in the first scenario I would use different Ip's on both the SkyBB or DM111P LAN port simply to allow easier administration (in this case they probably should be on different subnets).

Shouldnt see a problem as long as DHCP is turned off on the sky modem else you will end up with both of them trying to assign IP addy's

Lee

I hate to be picky and assume Re-Invented is just trying to help but I can't for the life of me see how his comment is actually correct in any of these scenarios:

In Scenario 1a the Netgear DHCP would know how to give you a correct DNS setting (assuming it has been setup correctly) and would respond with valid DHCP settings on its LAN/WLAN ports. However the DHCP on the SkyBB box (which is connected to the WAN port of the existing Netgear box) would and could never interfere with the existing Netgear box DHCP on the LAN/WLAN side (DHCP cannot traverse routers without a rather very rare DHCP Relay option). So there is no point in turing it off. Further in so doing it would only make it harder to configure the WAN port on the existing Netgear box (as you would have to manually set it and both the DNS and the Default Gateway settings).

In Scenario 1b it is not relevant as the SkyBB box is not used.

In Scenario 2 by default the Netgear box has no default knowledge of the Internet (on the WAN port of the other SkyBB box) as it's WAN port is not used thus its DHCP has incorrect knowledge of both the DNS and the Default Gateway and thus it would not work without manual configuration changes.

If someone can explain another scenario I would be very interested to learn!

I'm sorry if this confuses you but it is not so simple there are several key choices to make and if you plug the things together in the wrong fashion and don't do all the correct configuration work it will most definately not work for you in at least one way or another.

Personally I would ditch the SkyBB box and use a new dedciated Netgear DM111P modem in bridging (also called passthrough) mode. That is scenario 1b. If you need help with that or the other scenarios feel free to contact me (Rod) on 07876025797. It will be easier to explain and sort out on the phone.

[roddines]

Notes for the uninitiated:

ISP = Internet Service Provider (Sky Broadband in this example)
WAN = Wide Area Network (this can be a larger private business network or most usually the ISP network aka the Internet in the case of home networks)
LAN = Local Area Network (ie the local area network of servers and computers)
DHCP = Dynamic Host Control Protocol (ie it issues dynamically on connetion to the network the IP configuration info required for the connecting PC to talk to the local area and wide area networks).
MAC = Media Access Control (and refers to a network address assigned to the physical local network)

If you use scenario 2 make sure you disable the DHCP on the Netgear Rangemax (or whatever your equivalent is) otherwise it will compete randomly with the DHCP on the SkyBB Box and you will sometimes get OK DHCP info issued and occassionally bad DHCP info.

You only need to read on if you like to have a mind F*CK! (And don't bother if you cant understand English very well)

Theoretically it is possible to have both DHCP servers running in Scenario 2 so long as they are configured in the LAN IP setup to use two different non-overlapping ranges of IP addresses. ie SkyBB Box could issue 192.168.0.10-192.168.0.99 while the Netgear Rangemax could issue from 192.168.0.110-192.168.0.199.

However by doing this you cause other problems like not knowing which one is working properly or not, like when troubleshooting and thus if one is faulty or wrongly configured you may get random unexplained results. Also managing any DHCP IP exceptions/reservations becomes difficult and requires** all the devices that require static IP addresses on PC's, Printers and other devices to be set manually. **see below for an exception to this

For example you may have a network enabled printer or print server (thus enabling it to be shared with dependence on a running PC) and you want to install printer drives to access the printer directly. This requires the printer has a specific IP address. Normally you would create an exception/reservation in the DHCP configuration to ensure the MAC address of the printer is always assigned a specific IP address. However if there are two DHCP server they have two different ranges and thus one of them cannot assign a valid printer address. So you must set the printer address manually so it does not rely on the DHCP service.

**
To complicate things more in theory for a small range of addresses you could technically achieve this by overlapping the two ranges and setting the exceptions/reservations for all the overlapping addresses on both DHCP servers.
Example would be 192.168.0.10-192.168.0.109 while the Netgear Rangemax could issue from 192.168.0.100-192.168.0.199 and both would need to have exceptions for all the address from 192.168.0.100-192.168.0.109 which must be assigned to specific devices (MAC addresses..real or fake for future use) on both DHCP configurations.

However then the duplicity, maintenance and scope for errors that can occur negates any advantage (if any) in having two DHCP servers on the one LAN. Again to be clear the DHCP services do not bridge the WAN but functions only within the LAN.