How to allocate a /28

Network Technical Discussion
1

Hi guys, I need advice on how to maintain a /25 effectively without any hassles.

Allocating a /29 is pretty straight forward but my problem is allocating a /28 for a backbone link. How do I calculate that?

I tried using this site and this one but it confuses me. I am using the Wiki to keep track of IPs in use.

My main problem is the /28 allocation. any advice is welcome.

2

Saw that there was a discussion about something similar before

3

Hi Jen I normally just use Advance Subnet Calculator, it really helped me in the beginning. https://www.solarwinds.com/free-tools/advanced-subnet-calculator

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4

Hi thanks for the reply, I will give this a try. :slight_smile:

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5

http://jodies.de/ipcalc

This link works perfectly. If you are keeping track of the ips all you do is use the ip after previous address broadcast address (depding on your assigning could be ip address after network address)

Example if the last ip set you used ended 18.18.126 making 18.18.127 its broadcast eneter 18.18.128 and do a /28 calculate and should give you the result you looking

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6

@Firestarter made a Spreadsheet that apparently does all the calcs . The thread had to do with “adding someone to your sector” howto. Have you tried that?

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7

THIS VIDEO also made so much sense to me. Give that a try

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8

Hi Gekido, for example, if the next available range starts at 149.200 and I make it a 149.200/28 would that range consist of IPs from 149.200–149.213 ? being between the skipped 149.199 and 149.214

9

Thanks for the link, I will try all suggestions

10

149.200/28 the network would be 149.192 the broadcast would be 149.207. That being said everything inbetween those addresses is the usable addresses.

If you insert 172.26.149.200 and choose subnet /28 it would give you the same results i did using this site http://jodies.de/ipcalc

11

I saw that but because the network IP is 192 (which I already reserved as a 172.26.149.192/29) and the next available range after this would start at 200. is the confusing part. I thought that the /28 would continue like the /29s and just use 14 IPs instead.

12

It the way you calculate subnets. For your scenario you would need to do a 149.208/28 meaning you will have a /29 available before the /28

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13

Thanks Gekido, it makes sense now, At least I understand the way its calculated now, clears up the confusion.

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