Why Do ISP Give Customers A /28 subnet instead of /30 ?

foreverlearningforeverlearning Member Posts: 16 ■■■□□□□□□□
From what i understand in books, isp should be giving point to point /30 links.
Can anyone explain why they are giving customers /28 and how the network is designed?
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  • JDMurrayJDMurray MSIT InfoSec CISSP SSCP GSEC EnCE C|EH Cloud+ CySA+ CASP+ PenTest+ Security+ Surf City, USAAdmin Posts: 12,537 Admin
    edited September 2021
    /31 is a point-to-point link with two IP addresses. /30 is also two (usable) IPs and /28 is 14 usable IPs. Maybe the data plan the customers signed up for includes <= 14 IPs.
  • foreverlearningforeverlearning Member Posts: 16 ■■■□□□□□□□
    Yes. I agree with you. 
    But I wish to understand how ISP design the part of the network from PE to CE.
    How do they use the ip addresses? 
    Because I was taught that they use a /30. 
  • DevilsbaneDevilsbane Member Posts: 4,214 ■■■■■■■■□□
    I'm curious where you're seeing you've been given 14 usable IPs?
    Decide what to be and go be it.
  • foreverlearningforeverlearning Member Posts: 16 ■■■□□□□□□□
    I made a mistake it is a /29. 
    Meaning that there are 6 usable ip addresses.
    I am just curious though. If it is a point to point link (from PE to CE), how do they design the network part. 
  • SteveLavoieSteveLavoie Member Posts: 1,022 ■■■■■■■■□□
    I made a mistake it is a /29. 
    Meaning that there are 6 usable ip addresses.
    I am just curious though. If it is a point to point link (from PE to CE), how do they design the network part. 
    Consider yourself lucky to get handed out a /29,  the last /29 I asked for a customer, I had to justify every IP and get approval from the ISP. 
  • foreverlearningforeverlearning Member Posts: 16 ■■■□□□□□□□
    Can anyone working in an isp explain how they DESIGN a CE with /29 ?
    I have always learnt that ISP only give a /30.
    Learning how it is DESIGNED will be great.
    Thanks.
  • yparkypark Senior Member NoVAMember Posts: 118 ■■■□□□□□□□
    There's no "designing" if it's just a point to point link. Each side will agree on two IP addresses to use from the usable pool and that's configured on the interfaces. I've actually seen some ISPs do this but it's not the standard practice. The majority of the point to point links with other ISPs on our network are /31s. Some will use /30 and I have seen at least a few (out of thousands of PNI/transit point to point links) that have something bigger. It's just a waste of IP addresses but many big ISPs have huge IPv4 address allocations.
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