Anil's Blog

10.0.0.0/16 vs Comcast Xfinity

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Anil Vaitla
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1 min read

We started testing out tailscale the other day to help us connect to instances in our private AWS VPC (tailscale.com/kb/1021/install-aws).

Note that Tailscale uses the 100...* range for devices (tailscale.com/kb/1015/100.x-addresses). Furthermore our VPC in AWS was using 10.0.0.0/16 range:

AWS Ranges

We then setup subnet routes from our jumpbox (tailscale.com/kb/1019/subnets):

Subnet routes

Many folks were able to connect to machines in our AWS VPC when connected to tailscale but others were not. This was puzzling. For me I was able to connect to resources and saw a routing table as follows:

My Routes

For one person who wasn't working we noticed the following:

Bad Routes

We also noticed that there were many posts about VPN's not working with Xfinity wifi: forums.xfinity.com/conversations/your-home-..

So it looked like Xfinity was using the 10...* which collided with our AWS VPC space. Indeed this is their default modem setup:

Base Setup

Now we can reconfigure it to use 192.168.*:

New Setup

After reconfiguring their routes look as follows:

Working Routes

And finally we're able to access our AWS VPC space through tailscale. As an aside, I will no longer make any VPC as 10.0.0.0/16. I'll start at 10.175.0.0/16 at least.