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My company is in the process of getting another ISP connection in one of the data centers we co-locate in. Should our main internet circuit fail, we want to failover to this new ISP that has a diverse fiber path out of that data center. The current debate is whether we should get our own IPv4 public /24 and advertise our own space via BGP out via both providers; or lease IPv4 space from each (we're already doing this for our existing ISP connection), and have all public-facing devices have 2 IP's (and A records for those that have public FQDN's).

I know that you can't advertise out anything smaller that a /24 on the public internet, and obtaining a whole public /24 these days can be pretty expensive. We would also need to do this in another datacenter we are co-located in.

I'm curious to know what way people tend to be going when faced with this decision. I like the idea of our public-facing devices using the same static IP no matter what connection is active, but we don't have enough public-facing devices to justify paying for a whole /24 just for the convenience of that. Also, I know that there can be issues with DNS for A records with multiple public IP's.

What would be the better choice and why?

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The current debate is whether we should get our own IPv4 public /24 and advertise our own space via BGP out via both providers; or lease IPv4 space from each

For a clean failover you'd need your own /24 with BGP, sorry. Leased address space from an ISP is (usually) bound to that ISP and can't be used elsewhere.

Hypothetically, you could get both ISPs to share a /24 between them and lease you only a portion of it. Practically, the chance for them to cooperate is near zero.

all public-facing devices have 2 IPs (and A records for those that have public FQDNs).

Leaving the choice to connecting clients is not a failover. Depending on the software the clients are running, they might not try another IP if the first one from DNS lookup times out. In any way, they'd be facing serious timeouts and retries, likely during their entire session.

You could run your DNS records with a very short TTL and switch them over in case of failure. Due to DNS caching - possibly beyond TTL and beyond your control - that commonly takes a while and is not clean.

The only real solution is to obtain a /24 (they can be rented as well) and advertise over BGP. Anything else is just a little bit better than nothing.

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  • Thanks for confirming! I suspected as much, but didn't know if there as anything additional out there that I wasn't aware of. Apr 18 at 17:50

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