On Mon, Feb 23, 2015 at 10:02 AM, Eric Germann <ekgermann@cctec.com> wrote:
In spitballing, the boat hasn't sailed too far to say "Why not use 100.64/10 in the VPC?"
The only one I can see is if the customer has a service provider with their external interface in 100.64 space. However, this approach would have a more specific in that space so it should fire it down the tunnel for their allocated customer block (/28) vs. their external side.
Hi Eric, The main risk is more or less as you summarized it. Customer has no firewall or originates the VPN directly from their firewall. Customer buys a non-hosting commodity Internet product that uses carrier NAT to conserve IP addresses. The customer's assigned address AND NETMASK combined overlap some of the hosts you're trying to publish to them. Mitigations for that risk: Can you insist that the customer originate connections from inside their firewall (on RFC1918 space)? Most service providers using 100.64/10 either permit customers to opt out (getting dynamic globally routable addresses) or offer customers the opportunity to purchase static global addresses for a nominal fee. Are you comfortable telling impacted customers that they have to do so? A secondary risk comes in to play where a customer may wish to interact with another service provider doing the same thing as you. That essentially lands you back in the same problem you're having now with RFC1918. One more question you should consider: what is the nature of your customer's networks? Big corps that tend to stretch through 10/8 won't let their users originate VPN connections in the first place. They also don't touch 100.64/10 except where someone is publishing a service like yours. Meanwhile, home and SOHO users who are at liberty to originate VPNs might currently hold a 100.64/10 address. But they just about never use the off-bit /16s in 10/8. By off-bit I mean the ones with 4 or 5 random 1-bits in the second octet. My opinion: The likelihood of collisions in 100.64/10 increases significantly if you use them on servers. I would confine my use to client machines and try to put servers providing service to multiple organizations on globally unique IPs. Confining 100.64/10 to client machines, you're unlikely to encounter a problem you can't readily solve. Regards, Bill Herrin -- William Herrin ................ herrin@dirtside.com bill@herrin.us Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>