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Two IPs and routing paths to one server for redundancy



10:10 pm on Jul 6, 2010 (gmt 0)

5+ Year Member

Hi Everybody,

I would like to provide some redundancy. I have 2 DSL lines which each have several IP's from my ISP.

I have a server running on an internal network (e.g.

I have 2 ISP connections, we can call them connection 1 (e.g. and connection 2 (e.g.

I would like requests to a website (e.g. www.mywebsite.com) to be forwarded to both and My edge routers would then forward the request to the server (e.g.

It is particularly important to me that if either connection dies (as the router overheats! or the ISP fails!) then the remaining connection should be used to carry all the requests.

Thanks Everyone,


1:57 am on Jul 7, 2010 (gmt 0)

WebmasterWorld Senior Member lammert is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

Hi dsjbirch, first of all Welcome to WebmasterWorld!

I assume that your server is answering requests from global visitors on the DSL lines. Both DSL lines will have unique IP addresses for the outside world, so the first step is to have two A records in the globally visible DNS configuration for your domain name where each of the A records contain a public IP address of one of the DSL routers. Whenever a visitor requests the IP address for your website, it will be assigned at random one of the two IP addresses in your DNS setup. I.e. about 50% of your visitors will come in via DSL line 1, and 50% via DSL line 2.

When one of the DSL connection fails, 50% of the visitors will have a problem because they have been assigned the IP address of the connection which is down. That can be solved by using a DNS service provider which automatically temporarily removes A records from their round-robin scheme when the IP address associated with that A record becomes unavailable.

Because home Internet connections are not industry grade with a high guaranteed uptime, it is often better to move your server to a data center with higher quality Internet connections if the server gets significant traffic and generates significant income.


3:36 pm on Jul 7, 2010 (gmt 0)

5+ Year Member

Thank you kindly Lammert,

Can you recommend any DNS service providers which will remove the IP when it drops of the map? Does you know if register.com provides this service?


4:17 am on Jul 9, 2010 (gmt 0)

WebmasterWorld Senior Member lammert is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

Most registrars and hosting companies who offer DNS services don't offer the functionality for this type of automatic failover switching.

You can search on Google/Bing for search terms like DNS failover, dynamic DNS etc. You'll probably end up at specialized DNS providers like DnsMadeEasy, DynDns, UltraDNS etc.


12:14 pm on Jul 28, 2010 (gmt 0)

5+ Year Member

You can do round robin dns but the problem is you appear to be using completely the wrong approach for this. You appear to be using consumer grade dsl that optimised for downloading and not uploading

what you need to do is use an exterior routing protocol to advertise routes from both of your routers to your system.

This means that the internet knows there is two ways to get to your system if one route goes out of service the internet will use the other one.

However you need to run what in network terminology is called an AS (autonomous system) - you need to talk to your ISP to see if they offer this service and I doubt that on consumer dsl connections they will. A business SDSL ISP they might.


6:59 pm on Aug 1, 2010 (gmt 0)

5+ Year Member

Thanks Maurice, that's given me plenty to think about. I'm not sure my routers will support BGP or EIGRP. Are these the right routing protocols to brush up on? Can you explain what SDSL is? Do you know if BT supports that?


7:28 pm on Aug 1, 2010 (gmt 0)

WebmasterWorld Administrator incredibill is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

You really don't want round robin DNS as you described it, you want DNS failover.

Round robin DNS only gives the browser alternatives and it picks them randomly, if one fails I'm not sure it even tries the other, so a percentage of visitors would still be going to a dead connection.

If you're running Linux, Ultra-Monkey [ultramonkey.org] might be of interest.


2:31 am on Aug 2, 2010 (gmt 0)

WebmasterWorld Senior Member lammert is a WebmasterWorld Top Contributor of All Time 10+ Year Member Top Contributors Of The Month

@dsjbirch: SDSL is symmetric DSL where the speeds for upload and download are the same. Most DSL connections use ADSL (asymmetric) with a much higher download speed than upload speed. That is good for surfing the Internet from a home connection. But the other way--i.e. serving a website from a local connection back to the Internet--the bulk of the data will go in the slow direction, giving a less than ideal performance. SDSL connections are in general more expensive than ADSL connections.

BGP is supported on backbone grade routers which are much more expensive than the general ADSL router. But if your ISP supports BGP on an end connection (with a large IF), you may not need such a router yourself, because the whole routing table maintenance and updates actions should be on the ISP side of your connections, rather than on your own side.

@incrediBILL: The OP requested a solution where requests for the website would be forwarded to both IP addresses with redundancy. Round robin DNS where a failing IP address is removed (call it DNS failover :)) is the only payable solution for that which I know of.

With all this having been said, looking at costs and maintenance efforts, hiring a server (VPS or dedicated) in a data center might be a much more economical exercise than trying to make an high-available end-connection to a local server.


11:31 am on Aug 5, 2010 (gmt 0)

5+ Year Member

@dsjbirch @lammert

SDSL is the symmetric DSL which a lot of business isps will offer this C&W do and I am sure where in BT’s price list they will offer it. It is more expensive but compared to the cost of a real WAN link its dirt cheap - lookup the prices for a E1 (T1 in Yank speak) if you don’t believe me – when I looked it up you where looking at several K for the install charge

Re router if your wanting to do high availability you wouldn’t be using consumer routers any how – having said that you can run BGP on consumer routers the DDWRT replacement firmware will do this – or alternately ebay is you friend look for Cisco 2600’s with adsl modules.

As @lammert says your much better off outsourcing the hosting and letting the ISP /Hosting provider handle the routing issues


11:39 am on Aug 5, 2010 (gmt 0)

5+ Year Member

@lammert err backbone routers are things like the big routers at the top end product slike the CRS1 range (aka HFR and BFR) but any basic CISCO branch office router will do BGP.

HFR and BFR for Huge F^&*ING Router and Big Fu&*%ing Router and requires 3 phase power - now thast what i call a router

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