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DrDamnitFlag for United States of America

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ISP DHCP Range and Subnet

Question: What is the average DHCP scope or subnet for DHCP assigned addresses from cable / dsl providers?

Reason: I am configuring allowable logins to a server, and need to allow for users who log in from ISP assigned DHCP addresses to log in from any address in a range.

Example:
Right now, if I have someone logging in from a Verizon connection, and their current IP is 70.193.645.172, and I know Verizon uses a /24 network for each node, then I can allow all 256 addresses for that user, which means I don't have to worry about them being locked out if their IP address changes. If I knew it was a /22, I would have to allow 1,022 addresses.
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David Spigelman
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Not necessarily because, unless they are paying for that entire /24 block as a static block, that could change at any time. Normally it won't, but give it a month or two, and let them have a power failure - when they come back up, they might have an entirely different address set.

I would recommend one of two scenarios:
1. Make sure that they have a static IP address (or addresses) from their ISP, and just put THAT address into your rule set.
2. Use a VPN. But even there, you're going to need to use a remote-access VPN (i.e. using a VPN client on the users' workstations for it, because you will not necessarily know the IP address of their side.

If you want their entire network to be able to reach you through their router, though, you're probably going to want them to get a static address.
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giltjr
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ASKER

whois! Why didn't I think of that!
giltjr:

Please confirm you got the points for that solution.

-DrD.
Yes, got the points and thanks.  

Sometimes we overlook the simplest and most obvious solution. : )
Sometimes we overlook the simplest and most obvious solution. : )
Indeed.