Wisdom of using 100.64/10 (RFC6598) space in an Amazon VPC deployment

Mon Feb 23 15:52:36 UTC 2015

On Mon, Feb 23, 2015 at 7:02 AM, Eric Germann <ekgermann at cctec.com> wrote:

> Currently engaged on a project where they’re building out a VPC
> infrastructure for hosted applications.
>
> Users access apps in the VPC, not the other direction.
>
> The issue I'm trying to get around is the customers who need to connect
> have multiple overlapping RFC1918 space (including overlapping what was
> proposed for the VPC networks).  Finding a hole that is big enough and not
> in use by someone else is nearly impossible AND the customers could go
> through mergers which make them renumber even more in to overlapping 1918
> space.
>
> Initially, I was looking at doing something like (example IP’s):
>
>
> Customer A (172.28.0.0/24)  <—> NAT to 100.127.0.0/28 <——> VPN to DC <——>
> NAT from 100.64.0.0/18 <——>  VPC Space (was 172.28.0.0/24)
>
> Classic overlapping subnets on both ends with allocations out of
> 100.64.0.0/10 to NAT in both directions.  Each sees the other end in
> 100.64 space, but the mappings can get tricky and hard to keep track of
> (especially if you’re not a network engineer).
>
>
> In spitballing, the boat hasn’t sailed too far to say “Why not use
> 100.64/10 in the VPC?”
>
> Then, the customer would be allocated a /28 or larger (depending on needs)
> to NAT on their side and NAT it once.  After that, no more NAT for the VPC
> and it boils down to firewall rules.  Their device needs to NAT outbound
> before it fires it down the tunnel which pfSense and ASA’s appear to be
> able to do.
>
> I prototyped this up over the weekend with multiple VPC’s in multiple
> regions and it “appears” to work fine.
>
> From the operator community, what are the downsides?
>
> Customers are businesses on dedicated business services vs. consumer cable
> modems (although there are a few on business class cable).  Others are on
> MPLS and I’m hashing that out.
>
> 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.
>
> Thoughts and thanks in advance.
>
> Eric
>

Wouldn't it be nice if Amazon supported IPv6 in VPC?

I have disqualified several projects from using the "public cloud" and put
them in the on-premise "private cloud"  because Amazon is missing this key
scaling feature -- ipv6.   It is odd that Amazon, a company with scale
deeply in its DNA, fails so hard on IPv6.  I guess they have a lot of
brittle technical debt they can't upgrade.

I suggest you go with private cloud if possible.

Or, you can double NAT non-unique IPv4 space.

Regarding 100.64.0.0/10, despite what the RFCs may say, this space is just
an augment of RFC1918 and i have already deployed it as such.

CB