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Frequent Contributor I

Flat networks....

I'm talking really flat.....   we are reworking ip space for our campus and have now gotten  a sizeable chunk of contiguous space for our wireless and housing networks.   I had previously used vlans pools - had 11 /22's..... was a bit concerned - but had the bcast and mcast controls in palce... it worked really well.


Was looking at an optimum # of vlans for vlan pool hashing to work with... and well I bet using one vlan would give me the most even distribution accross all vlan(s)... but  I'm looking at using /18's


actually thinking of a /18 and multinetting on few smaller subnets for good measure.


does going so flat present any issues if I wanted to do some fancy airgroup tricks in the future?


anyone have any glowing reports from flatland?  or tales of horror and woe as the plains were flooded with uncontrollable layer2 protocols...(or worse?)




Also as a follow up - assuming flatland is happyland.....    any compelling reasons to keep my captive-portal ssid on separate ip space from my 802.1X ssid - and let the controller and roles maintain the security separation?





Guru Elite

Re: Flat networks....

Thanks to bcast/mcast optimization, there are some very, very large subnets on Aruba wireless (/16) with features like AirGroup in use.

It's best to work with your Aruba SE on this.

| Tim Cappalli | Aruba Security | @timcappalli | timcappalli.me |

NOTE: Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba or Hewlett Packard Enterprise.
Frequent Contributor I

Re: Flat networks....


I am working with my SE.  Have heard that people have been using very flat networks.


My experience with /22's and using the bcast/mcast mitigation options - leads me to beleive this should be fine.   Just wanted to get some direct feedback from anyone else who has gone flat.


Get some info direct from the horse's mouth...  :)



Contributor I

Re: Flat networks....

I am going to be attempting to launch a /21 with BC/MC Optmiization soon, I'll write back how it goes! :)

Occasional Contributor II

Re: Flat networks....

I have two /19's deployed on different controllers and see a high so far of about 50% address space utilization in each. No problems so far.... Previously, I had pools of /23's and /24's.


Super Contributor I

Re: Flat networks....

I assume you're PATing those /19s. To what sized networks are mapped?

Ryan Holland
Senior Network Engineer
The Ohio State University
Office of the Chief Information Officer
TNC, 320 W 8th Ave., Columbus, OH 43201
614-292-9906 Office
holland.112@osu.edu ocio.osu.edu

(sent while mobile)
Ryan Holland, ACDX #1 ACMX #1
The Ohio State University
Occasional Contributor II

Re: Flat networks....


Actually, I have two /19's that are private address space and each is PAT'd to a public /24. I also have two other /19's that are public and are not translated.




Frequent Contributor I

Re: Flat networks....

So are you multinetting those /19's


I'm looking to multinet a /18 and /19 onto one vlan.


Flatland sounds good from my pervious experience with /22 and what others have reported.


What specific BC and MC controls are in place?

I've been using the following

per VAP:

Drop Broadcast and Multicast

Convert Broadcast ARP requests to unicast


Are their other controlls I should be putting in place?





Occasional Contributor II

Re: Flat networks....

I'm running flat networks at my location; 4 /16's
we do not allow inter-user communication

we do not allow multicast/bcast  (Except for on 1 SSID in a limited number of locations)

Things work well for the most part. 

We do have a problem with constant gratuitous arps from across campus going everywhere.

Wireshark is continuously scrolling on these GARPS alone.

Frequent Contributor I

Re: Flat networks....

Slightly side-track issue.....   but is there really no way to multi-net on the aruba controllers.


specifically I can not have multiple ip subnets defined on one VLAN.


Looking around - appears I can create secondary ip interfaces on the wired switches .  Is there a different way to set this up on the controllers - or is just not a currently supported feature?



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