Using IPv6 for multihome ISP eBGP peering due to IPv4 public /24s no longer available

Question

• Problem:

I have two routers, and two separate ISPs (two different public ASNs). I wish to accept full BGP routes in order for us to properly set up true reliable ISP failover in a way that allows both links to be utilized. From my understanding, the only truly effective/reliable way of doing this is by accepting full routes and advertising my public ASN to the internet.

The problem here is that obtaining a public /24 IPv4 block of addresses is not possible due to cost/lack of IPv4 public address space. Additionally, the LAN/intranet network must remain IPv4 on the "backend".

• My question is:

Is it possible to leverage the untapped IPv6 public IP address space and use that in lieu of a public /24 IPv4 block in order to advertise our public ASN out multiple providers (and therefore, provide the flexibility and control needed in order to manage those multihomed connections)?

The key here is that IPv6 would ONLY be used to allow us to accept full routes and advertise our public ASN across both providers. The backend (literally the entire LAN/intranet) would have to run strictly on IPv4.

Is this even possible? If so, what are the limitations?

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Follow-up question: How do people in modern times (i.e. mid 2010s) tackle this multihoming problem when they are unable to obtain a /24 public IPv4 block?

For more clarity, the ultimate goal is the ability to utilize both ISPs at the same time for every day traffic flow to the point where if a current video conferencing session over one ISP was to fail, it would automatically re-route and continue working over the other ISP.

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Edit:

Note: For the sake of this question, it is not possible to a) use IPv6 on the LAN/Intranet side instead of IPv4 and b) Somehow obtain a /24 public IPv4 block by purchasing it from a third party.

Answer 1

You can certainly run eBGP with your ISPs with IPv4 and receive the full IPv4 Internet prefixes to use in outbound routing; you just can't advertise your prefixes that are longer than /24. That has nothing to do with IPv6.

IPv4 and IPv6 are two completely separate protocols. Advertising and receiving IPv6 prefixes will not do anything for your IPv4 routing.

If you only exchange IPv6 prefixes with your peer ASes, then your routing tables will only have the Internet IPv6 prefixes, not the IPv4 prefixes that you seem to want, you still cannot advertise your IPv4 prefixes to the Internet unless you have /24 prefixes.

You should still head toward IPv6. Get that set up, too, and start adding IPv6 to your network. That is the direction the world is heading, and putting it off will be painful in the long term.

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Edit:

Note: For the sake of this question, it is not possible to a) use IPv6 on the LAN/Intranet side instead of IPv4 and b) Somehow obtain a /24 public IPv4 block by purchasing it from a third party.

Based on your edit, you have a problem. If you want to advertise your IPv4 prefix(es) on the public Internet, you are going to need a public IPv4 prefix of /24 or shorter. That is simply all that the ISPs will advertise. If you cannot get one on the open market, for whatever reason, then you cannot advertise your IPv4 prefix(es) on the public Internet. This is the reason the Internet must transition to IPv6; there just are not enough IPv4 addresses to support the needs of everyone.

IPv6 doesn't "fix" IPv4, it replaces it.

You can certainly add IPv6 support to your network. You don't need to completely replace IPv4 on your network at this time. You can dual-stack your network with both IPv4 and IPv6. Most people now have access to the IPv6 Internet, too. You will eventually need to support IPv6, and the longer you put it off, the more painful it will be.