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I work at a company where I am partly responsible for IT, just because I'm semi technical and we're not big enough to warrant a dedicated role for someone else. I was asked to look into upgrading out network connection. We are looking to upgrade our work network to a fibre connection, and one of the discussions I had with the provider they mentioned the number of IP addresses we would be given. I was told that since we would be given a /30 address that we would be given two usable IP addresses. I would just like to understand, if a /30 should mean 4 working addresses, what are the other two used for? Why don't we get to use all of them?

Also, since we have other branches (3 other branches), our firm's boss told me to ask about MPLS. With MPLS, apparently we would need to have more than the /30 addresses, and they gave more technical detail that I did not understand. With the LAN hidden behind the router, why would we need more IP adresses? Why does MPLS need more IP addresses?

  • Which MPLS service are you buying: L3VPN, EoMPLS, VPLS, or something else? – Mike Pennington Feb 3 at 0:19
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First question is how are the addresses in a /30 used? You are correct a /30 does have 4 usable IP Addresses, however, typical network guidelines reserve the first and last address of a range for the Network Address and the Broadcast Address, leaving just 2 usable IP addresses. Is this required? No, but only in a crunch should you disregard this rule. So for example:

First /30
10.10.10.0 - Network Address
10.10.10.1 - 1st Usable IP Address
10.10.10.2 - 2nd Usable IP Address
10.10.10.3 - Broadcast Address

Second /30
10.10.10.4 - Network Address
10.10.10.5 - 1st Usable IP Address
10.10.10.6 - 2nd Usable IP Address
10.10.10.7 - Broadcast Address

Third /30
etc...

Second question about MPLS is a bit awkward and I'm not for sure I understand what you are saying/asking. MPLS is a technology that still requires IP address but it allows you to have multiple customers riding the same network and be completely isolated from one another and their address ranges overlapping. From your perspective you will be an end user of an MPLS cloud potentially so you it will not impact you. You will set an IP address on your CE (Customer Edge) device and they will have an IP address on their PE (Provider Edge) device and like black magic all your sites will have the ability to talk to one another basically. There is a lot to MPLS, but being you are a customer you really don't need to know any of the details about how MPLS works.

Sounds like you got thrown into the fire! Good luck.

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