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New Member

How would you allocate IP addresses in this topology?

Hello. This is a call for opinions.

I have a current network that I will be replacing in parallel. I have 15 Class B addresses (24 bit subnet), for illustration, let's assume the address range 10.10.l.0/24 to

The network is an air-gapped, secondary network running through a campus and MAN. The user base is widely dispersed, has a small frequency (2-4 user groupings) and has an unknown future growth. Legacy network is not documented - unknown amount of current users. Alot of variables, right? Welcome to my world.

Anyway, I'm looking at the best way to allocate this IP address space so that I have reasonable scaling, room for growth, logical grouping, etc.

I haven't decided on a core or collapsed core yet - althought today I am leaning to the collapsed core.

Lets assume some type of baseline:

1). 22 buildings throughout the campus and MAN

2). Average of 4 floors per building (four buildings have 8,9,11,12 stories), the rest have 4 or less).

3). Currently have an equal amount of IP addresses allocated to the legacy LAN. Current IP space is discontiguous and not logically grouped and heavily subnetted. Total of 3680 addresses allocated - not necessarily implemented.

4). Users are not geographically or logically grouped. Usually in pockets of 4-8.

5). Mail and DNS services only on intranet. All other communicaton is with external entities. (not a big need for internal communication).

6). NAT and DHCP are not an option.

Obviously, CIDR and VLSM are needed. I wish to leave a range available for point to point networks between a core and distribution layer, in the event a core is decided on, rather than the proposed collapsed core. I'm seeking a way to allocate the given IP range in a heirarchical manner so that route summarization is efficient and flexible while accommodating a growing user base.

I can respond to additional questions as our scenario grows.. any thoughts so far on how this can best be laid out?


Re: How would you allocate IP addresses in this topology?

So, my suggestion would be to allocate general ranges for each area of the network, to provide for heirarchy and summarization. Within each range, use long prefix lengths (small network ranges), but don't put any two sets of users together. This would get you the ability to grow any given set of users up or down as needed, but simply adding two contiguous blocks together.

As for the point-to-points, think about unnumbered or using /31's to get the address range needed down as low as possible.


New Member

Re: How would you allocate IP addresses in this topology?


I am having a hard time visualising the layout of these buildings, and it might help in the deisgn. You say uou have 22 buildings, do they all have a direct connection back to a central location, or do they daisy-chain between each other, a little of both? The physical topology will be useful when deciding IP allocation.

New Member

Re: How would you allocate IP addresses in this topology?

Both. Some have serial connections ( MAN nodes), others run to a central comms center or to a nearby major node. This ambiguity leads to the wavering on whether to do a core or collapsed core. Suffice it to say, the decision will come down to a level of redundancy and management rather than a cabling issue.

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