DHCP scope running out

[TGF_Cisco]

hello

We have  a wireless network currently with DHCP giving IP address for our internal users

The current subnet accomodates 1024 users  . We would like to extend the scope to include more users.

The DHCP is configured with the following range

172.19.180.0 - 172.19.183.255               

and the dhcp for another network  is on the controllers 172.19.190.0/24

We would like to increase the scope for our internal users to accomodate 5000 users.

So this mean I need to recreate the scope on windows 2008 R2 server with a starting IP address 

The ASA is configured as a default gateway and my concern is that the subnet that I will have to use then would be 172.19.176.0 - 172.19.191.255 which overlaps with another network.

How do I go about it?

[Marvin Rhoads · Accepted solution]

You need to either pick a DHCP scope that does not create conflicts with any of your existing networks or break apart your wireless networks to use multiple scopes (recommended).

It's generally not a good idea to create such huge layer 2 broadcast domains (thousands of users) since it can create performance issues with the amount of broadcast traffic from that many host - especially on wireless networks.

[TGF_Cisco]

In terms of setting it all up by splitting it all up.

Can you confirm if this would work

• •1.       Increase the existing scope to 172.19.176.0 - 172.19.183.255 on dhcp server (2048 )
  
  • •a.      Change the subnet in ASA
    
  • •b.      I believe I can still keep the default gateway as before (172.19.180.1) .. just need to add the right exclusions in the DHCP server
    
  • •2.      Create a new interface on the controller and assign it an IP 172.19.168.x and create new IP subnet 172.19.168.0 - 172.19.175.255 on dhcp server ( another 2048)
    • •a.      Route it through on our network
      
    • •b.      Assign the same SSID as the one already created for our corporate wireless
      

have i missed any steps?

Regarding my idea of creating a huge scope, I thought controllers do not allow broadcast by default. How could it affect performance?

thanks

[TGF_Cisco]

Hello can someone please help

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[paul driver]

Hello TGF,

For your wireless clients,as they are roaming  you can drop your lease times to a relative small values ( 2 hrs)

Now to expand your dhcp socpe.

If you need more dhcp ranges,it is better as marvin have suggested to create smaller broadcast domains instead of having one large one for reasons stated.

For the new scopes will require addtional work:

1) wintel dhcp server - new dhcp scope defined actived and authrorised

2) new svi relating to the new scope on your core or asa &/or wlc

3) dhcp relay ( ip helper address) if appilcable

4) necessary ssid for new svi if applicable

res

Paul

Please don't forget to rate this post if it has been helpful.

[TGF_Cisco]

Could you look at below and confirm
In terms of setting it all up by splitting it all up.

Can you confirm if this would work
•1. Increase the existing scope to 172.19.176.0 - 172.19.183.255 on dhcp server (2048 )
•a. Change the subnet in ASA
•b. I believe I can still keep the default gateway as before (172.19.180.1) .. just need to add the right exclusions in the DHCP server
•2. Create a new interface on the controller and assign it an IP 172.19.168.x and create new IP subnet 172.19.168.0 - 172.19.175.255 on dhcp server ( another 2048) •a. Route it through on our network
•b. Assign the same SSID as the one already created for our corporate


Would you recommend using ap groups or the above method will work well ?

I haven't used same ssid with different scope before nd hence need advise


Sent from Cisco Technical Support iPad App

[paul driver · Accepted solution]

Hello TGF,

1)providing it doesn't overlap as you stated - yes

a)yes = change the subnet to acomodate the new ip range

b) yes = no need to change D/G

2) what wrong with the existing interface from the above  or is this a different one?

On the dhcp server you will need to delete the existing scope and reapply it with exclusions as before with the new subnet  range - so yes

the above method should work- but it will be one big subnet!

I would suggest keep in mind dropping the lease timings for the wlan guest clients to a small time window so to reserve future dhcp starvation.

res

Paul

Please don't forget to rate this post if it has been helpful.