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I'm working at a messy location,

one of the strange (for me) things is that on the same physical network there are two different subnets. Specifically some computers will have 10.0.0.0/24 and some others will have 172.16.0.0/24. There is only one DHCP server, which gives IPs on the 10.0.0.0/24 range, and there are two internet gateways, one with IP 172.16.0.1 and one with IP 10.0.0.1 .

To give an example, I can easily swap one PC from one subnet to the other just by changing its IP and gateway settings.

I am trying to imagine why they created the network this way, and which may be the possible advantages and/or drawbacks of having two different subnets on the same physical network.

Any thoughts?

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    If I had to hazard a guess, I'd say they added a 2nd ISP Gateway and didn't know how to load balance them, so they stuck them on another subnet and charged forward. @EEAA's comment about seeing this often totally holds true for me as well. most of the time it's an amateur trying to fit a square peg in a round hole. I had a client using 169.254.x.x as their local subnet because they didn't understand how to setup a DHCP server and just waited for windows to time out... it was like that for YEARS... – MikeAWood Oct 22 '13 at 00:33
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    The first thing I would do would be to inventory and audit each subnet to determine which hosts are on which to see if you can determine why it's been configured the way it is. It could be that all user traffic transits one subnet (and gateway) and "public" services (web site, etc.) transit the other subnet (and gateway). Just because it's unorthodox doesn't mean it's wrong. – joeqwerty Oct 22 '13 at 03:27

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Ugh. I see this quite a bit.

Who knows what the original reason was, but it's highly likely that it was one of:

  • laziness
  • lack of budget for proper switchgear
  • ignorance of how to do things properly

I have never come across a good technical argument for why this would ever be a good thing. You're best to try and un-do the mess posthaste.

EEAA
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