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1 DNS server on 2 ISP's

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#1 Lyndon0326


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Posted 19 December 2017 - 06:11 AM

Hi Gurus!


First I would like you to know that Im a newby on site, just got some few inquiries regarding Networking and hopefully I can find solutions here. It would be a great help on my company if problem resolved. 


So here's a network summary I am facing right now.


We recently subscribed from an ISP for backup purpose, simply means we are currently running on 2 provider. Now with these, I wonder if my network topology will work since I only have 1 DNS server for users/machines and I wanted to link this to both ISP with 2 different LAN subnets ofcourse. Would that be possible? I have attached my network design and hoping you to suggest if you find it wrong or whatever you think it would be good at the end. 


Thank you in advance!

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#2 MasterNe0


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Posted 20 February 2018 - 04:23 PM

Not sure why you need two different LAN subnets. You could just get a router that can support 2 ISPs. Some cisco routers have this option and we done this also for using a sonicwall. If Primary ISP goes down, it switches to secondary.


Having two LAN subnets will probably cause more work for you as you need to manually swapped machines from one subnet to another and will probably causes issues with machines talking to each other on your SUBNET.


Only issue is mail doesn't work if you host internal (unless you manually swapped A Records to the backup ISP during the outage).

Edited by MasterNe0, 20 February 2018 - 04:24 PM.

#3 Orecomm


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Posted 21 February 2018 - 05:29 PM

The attached design didn't make it, and your explanation isn't quite clear. If I could ask a few questions to clarify:


Is the single DNS server you are referring to resolving INTERNAL addresses on your local, internal LAN, or EXTERNAL addresses as seen by the Internet at large and pointing to things like your mail and web servers? Where does this DNS server LIVE in relation to your network, is it local to your LAN or out in the Internet somewhere?


As with MasterNeO, I don't see a reason you would need, or want, two local LAN subnets just to support a backup ISP connection. Is there something we're missing here?

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