Supernetting IPv4

[zekebashi]

Hello,

I have a 10.1.243.0/24 subnet that I would like to further subnet so I have 128 subnets that I would like use with /30 prefixes. 

10.1.243.0/25

10.1.243.1

10.1.243.126

10.1.243.127

What would be the best method to accomplish this?

Thanks in advance,

~zK

[paul driver]

Hello

review the attach xls document i created some while back, it may assist you.

[zekebashi]

Thanks for sharing the spreadsheet. So, for this particular requirement that I have, it looks like I can use the /31 to be able to have 128  subnets, correct?

I've reviewed this RFC3021 and it explains that there are some limitations with using this /31 in relation to broadcasting; however, the doc, also, explains that there are no impact to the routing. Section 2.3 "

  Networks with 31-bit prefixes have no impact on current routing
   protocols.

I will be using these links to connect access-layer switches to dist switches. The goal is migrate from the current configuration where the access-switches are connected to a pair of C6504 switches using L2 Port-Channels.

Are there any other concerns or considerations that I should be aware of?

Thanks for your input.

Best, ~zK

[paul driver]

Hello

The only reason you allocate addressing to a L2 host switch is for mgt reachabiltiy you can relocate them without any addresss and should be fine.

Why is it that you require so many subnets when you could just split that /24 into two /25 subnets and use one of them for your switches mgt vlan (126 hosts)

[zekebashi]

Current topology has the access-layer switches uplinked to a pair of dist-layer switches via L2 Port-Channels. I made the recommendation to my client to covert/migrate the L2 links to L3 P2P links. There is a total of 90 L3 uplinks, thus, I selected the closest CIDR to the 90 number which is 128.

I need to brush up on my subnetting skills. :-) .. So, I could choose, for instance, this 10.1.243.0/24 subnet and split it into two subnets (see below) and then take of the /25 subnets and split them into /30 subnets, such as

First /25 subnet:

1st /30 subnet:    10.1.243.0    10.1.243.1 - 10.1.243.2      10.1.243.3

2nd /30 subnet:   10.1.243.4    10.1.243.5 - 10.1.243.6      10.1.243.7

3rd /30 subnet:    10.1.243.8    10.1.243.9 - 10.1.243.10    10.1.243.11     

...

Second /25 subnet:

1st /30 subnet:    10.1.243.128   10.1.243.129 - 10.1.243.130      10.1.243.131

2nd /30 subnet:   10.1.243.132   10.1.243.133 - 10.1.243.134      10.1.243.135

3rd /30 subnet:    10.1.243.136    10.1.243.137 - 10.1.243.138      10.1.243.139  

Network Address	Usable Host Range	Broadcast Address:
10.1.243.0	10.1.243.1 - 10.1.243.126	10.1.243.127
10.1.243.128	10.1.243.129 - 10.1.243.254	10.1.243.255

Is this correct?

Thanks in advance,

~zK