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Ask the Expert- SD-WAN

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Beginner

Dual ISP

Hi All

I have a datacenter in which we have MS Exchange,  2-3 web application    which are accessed from internet.

One ISP had given me 59.x.x.x/28 and other has given 14.x.x.x/28 subnet. With ISP I am using static routes for routing. Both links are termination on two diffrent cisoc router.

Currently for each internet application I have assigned one IP from ISP A and one from ISP B range to fullfill redundancy. Now if ISP A links goes dowm DNS on internet still resolved to 59.X.X.X and application cannot be used.

How should I use two ISP links so that I do not have to worry about DNS? Also we are using a service provider for DNS services.

What is the best practice and design for multiple ISP?

Thanks

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Beginner

Dual ISP

Hello Deepak

The best practice would be to have your own public IP space from regional IP registrar (like APNIC for asia pacific) and get it advertised to both the ISPs and have DNS A record entry pointing to your IP which is reachable through either of the ISPs.

Other option can be to have DNS functionality at your end with some intelligence.  ISP DNS will have NS records pointing to your DNS for getting actual application IP address.  Your DNS must be able to identify, which ISP is UP or DOWN and return appropriate public IP (can be from ISP1 or ISP2).

regards

Bharat

4 REPLIES 4
Beginner

Dual ISP

Hello Deepak

The best practice would be to have your own public IP space from regional IP registrar (like APNIC for asia pacific) and get it advertised to both the ISPs and have DNS A record entry pointing to your IP which is reachable through either of the ISPs.

Other option can be to have DNS functionality at your end with some intelligence.  ISP DNS will have NS records pointing to your DNS for getting actual application IP address.  Your DNS must be able to identify, which ISP is UP or DOWN and return appropriate public IP (can be from ISP1 or ISP2).

regards

Bharat

Beginner

Dual ISP

Hi Bharat

Thanks for the reply. We are a small business and we require only 16 or 32  IP address. Can I get such a small subnet from IP registrar.

Thanks

Deepak Khemani

Frequent Contributor

Dual ISP

no. minimum subnet is /24

ask your service providers to give you reserve links

Beginner

Dual ISP

Hi Deepak

You need to look for link load balancer with NAT and DNS features.

Regards

Bharat

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