Understanding of DNS, DHCP, and OpenVPN Assigned IPs

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gearond
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Understanding of DNS, DHCP, and OpenVPN Assigned IPs

Postby gearond » Tue Jul 21, 2015 4:24 am

I am about to try to set up a dedicated OpenVPN server on Amazon VPC. Notice I said 'try' :-) I almost never get things right first time. But It usually is better when I understand how things work AND how to make adjustments.

I have a VPC with a net and range of 10.0.0.0/16. So it will never conflict with the default, OpenVPN administed connection IPs from 10.8.0.0/8. (From what I can tell from RTFM) I'm a little new to networking, so I need to know about something. Before I do any routing table changes in the VPC, will traffic from a client get to any servers in the VPC or visa versa? This is what I really don't understand. Since the whole VPC only has a range from 10.0.0.0 - 10.0.255.255, but the OpenVPN IPs will be from 10.8.0.0 - 10.8.0.255, and that subnet is not part of the VPC range, how are the packets allowed, just routing table entries?

Also, in client mode, connecting from a Peetz Coffee shop, will any other people there on that subnet be able to see the servers on my VPC?
How about in Bridging mode?

Finally, for those with experience in Amazon VPC admin< I did see SOME mention of routing table entries to allow some kind of connection. Is it possible to put that routing table entry at some kind of global level within the VPC?

Thank you for your kind answers.

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maikcat
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Re: Understanding of DNS, DHCP, and OpenVPN Assigned IPs

Postby maikcat » Tue Jul 21, 2015 6:17 am

have a VPC with a net and range of 10.0.0.0/16. So it will never conflict with the default, OpenVPN administed connection IPs from 10.8.0.0/8.


nop 10.8.0.0/8 is like 10.0.0.0 so yes its conflicting with 10.0.0.0/16 try to use 16 bit mask as well.

Michael.

gearond
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Re: Understanding of DNS, DHCP, and OpenVPN Assigned IPs

Postby gearond » Wed Jul 22, 2015 1:20 am

I must not really understand IP subnetting at all. My belief is that they were totally separated by 7*65536 addresses. If it were 10.0.8.0/8, then I'd believe that they'd clash, but 10.8.0.0/8 shouldn't be in the range of 10.0.0.0/16, right?

And, FYI, I haven't tried yet, I just want to understand and plan multi country VPCs/subnets on Amazon AWS. I feel it's better to avoid the Oh CRAP! situation of 'We can't use this VPC range because we have put all the VPNs in a bad spot.

Plus, the question is also about how the VPC and it's subnets can see 10.8.0.0/8 addresses.

But, one of the tutorials here may have helped me understand. When I'm sure, I'll post it to this thread so others can find it.

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Traffic
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Re: Understanding of DNS, DHCP, and OpenVPN Assigned IPs

Postby Traffic » Wed Jul 22, 2015 11:16 am

gearond wrote:10.8.0.0/8 shouldn't be in the range of 10.0.0.0/16, right?
Wrong .. Subnet Mask:
10.0.0.0/16 is in the range 10.8.0.0/8 [10.0.0.0 - 10.255.255.255]
10.0.0.0/16 is not in the range 10.8.0.0/16 [10.8.0.0 - 10.8.255.255]

gearond wrote:I must not really understand IP subnetting at all
indeed:
https://en.wikipedia.org/wiki/IPv4_subnetting_reference

gearond
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Re: Understanding of DNS, DHCP, and OpenVPN Assigned IPs

Postby gearond » Wed Jul 22, 2015 12:51 pm

Ah yes, I always confuse '/8' vs '/24'.


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