The company I work for have branches all over Europe and data centers in Sweden and Germany. In Sweden all sites are connected to each other via point-to-point links as well as each connected to Internet. Outside Sweden the sites are only connected to Internet (with IPsec links to Sweden).

We want to roll out multihoming on all sites and thus will apply for a RIPE membership to get one of the last IPv4 /22 networks left as well as an AS number.

  1. Is it provider-aggregatable address spaces that RIPE assigns? Can we do multihoming with these addresses? Can I later switch one or several of my providers?

  2. Can you subnet you assigned address space and use it on two "isolated" networks. I.e. can we have a subnet with transit providers in Germany and another subnet with other providers in Sweden? Or do I need one AS number for each isolated network? If so, can I get multiple AS numbers?

All help/input would be grately appreciated!

Thanks and regards, Par


You can do multihoming with any address space you get from RIPE NCC. The difference between PA (Provider Aggregatable) and PI (Provider Independent) is what you are allowed to do with it.

  • PA space is for LIRs (RIPE NCC members, often ISPs or large companies, but these days also smaller organisations needing that last /22) to be used to number their own infrastructure and that of their customers (if any).
  • PI space is for other organisations that need address space for their own use. These addresses are not allowed to be assigned/delegated to third parties.

But in the end they are just blocks of integers :) There are no technical differences between them, only policy differences. You can use them independently of ISPs, connect them to multiple upstream ISPs (multihoming), change those upstreams, participate on internet exchanges etc. The last /22 you can get is PA space so you are allowed to assign/delegate addresses to third parties if you want to.

Splitting up your allocation from RIPE NCC is possible. There are no rules about this, only conventions. For IPv4 you can usually deaggregate down to a /24. Splitting your /22 into two /23s will therefore work.

If you have two disconnected networks you need two AS numbers. To prevent routing loops BGP filters out AS paths that have your own AS in them. If you would use the same AS then your network in Germany wouldn't be able to see the network in Sweden and vice-versa. You can get multiple AS numbers if you have multiple routing policies. As your routing in Germany is different from your routing in Sweden you qualify for that so you should have no problem getting two AS numbers.

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