Routing Public Subnets with 2 ISP's?

  • Hi All

    I was planning on setting up a CARP cluster and using 2 ISP's for added redundancy.

    From each of the ISP's I would get 3 x public WAN Ip's. I also need a public /28 subnet from one of the ISP's, I was planning on putting the /28 on an optional interface.

    My question is this.

    If the /28 was from ISP #1 and ISP #1 goes down, how do I make sure I can still get to servers on the /28 over my connection with ISP #2?

    Is this even possible? How would ISP#2 even know I had that /28 network.

    My first thought is that ISP#2 would need to have a static route on their end pointing to the 3 WAN IP's I got from ISP #2, am I on the right track?

    Thanks for your help

  • You would need to run BGP with your own ASN number I think in order to route your public IP's over multiple providers.  An ISP provided network range typically will not route over another provider's network.


  • How do you get an ASN?

    Is the ASN then related to a public IP block?


  • I would recommend getting another subnet for the second ISP too. There are DNS-services that can check servers for responsability and switch the nameresolution to different IPs if the main IPs are not working anymore. This way clients would get the IPs of ISP2 resolved if ISP1 goes down. You even could do a loadbalancing between both ISPs this way. There are DNS-services supporting this too. I know scott is working on a dns-package for pfSense doing things like this. Afaik it's nearly done.

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