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Community Member

Extending DHCP scope by adding a secondary IP range to same vlan?

Hi,

 

Current dhcp scope is running out of IPs and would like to add a secondary IP range for vlan 50 and I was hoping the following will work. Extending the current ip range is not an option at the moment, so the PC's connected to switch ports configured for vlan 50 will pick up addresses from both ranges...

I was hoping someone can clarify if the following scenario will work or not or can foresee any problems with it, HSRP is also included, will this be a issue?:

 

Sw1:

interface Vlan50
 ip address 192.169.12.1 255.255.255.0 secondary
 ip address 192.168.10.1 255.255.0.0
 standby 1 ip 192.168.10.254
 standby 1 ip 192.169.12.254 secondary
 standby 1 priority 110
 standby 1 preempt

 

Sw2

interface Vlan50
 ip address 192.169.12.2 255.255.255.0 secondary
 ip address 192.168.10.2 255.255.0.0
 standby 1 ip 192.168.10.254
 standby 1 ip 192.169.12.254 secondary
 

sw1 and sw2:

ip dhcp excluded-address 192.168.10.1
ip dhcp excluded-address 192.168.10.2

ip dhcp excluded-address 192.168.10.254
ip dhcp excluded-address 192.169.12.1

ip dhcp excluded-address 192.169.12.2 

ip dhcp excluded address 192.169.12.254

ip dhcp pool pool1
 network 192.168.10.0 255.255.255.0
 dns-server 4.1.1.1
 default-router 192.168.10.254
!
ip dhcp pool pool2
 network 192.169.12.0 255.255.255.0
 dns-server 4.1.1.1
 default-router 192.169.12.254

Everyone's tags (1)
6 REPLIES
Bronze

It won't work, you can only

It won't work, you can only assign one address dynamically!

In addition you have two separate networks, so nodes would not be able to communicate with each other.

One final note, is that it is an 'illegal' address, i.e. it is not from the reserved private network classes.

Martin

Community Member

Hi cmartyn, Sorry forgot to

Hi cmartyn,

 

Sorry forgot to mention the above config is isolated in a test lab environment and will not be using these addresses in the production environment.

 

I tested in a lab environment and I was able to assign the two laptops with an ip address, one from the  192.169.12.x and one from the 192.168.10.x range and both laptops were connected to switch ports configured for access vlan 50.

 

So it seems to work......

 

 

 

Bronze

But those two hosts won't be

But those two hosts won't be able to communicate, as they are on different networks?

Martin

Community Member

hey cmartyn,Just tested each

hey cmartyn,

Just tested each laptop which is sitting on different network but same vlan and are able to ping each other...

Bronze

I was not sure how the

I was not sure how the routing would work, as you are not inter routing between VLANS, none the less it must be, else you would not be able to communicate between the two!

It's interesting re the DHCP though, it may be that you won't know for sure which node will use which pool?

Martin

Community Member

Hi cmartyn,I've just checked

Hi cmartyn,

I've just checked the routing table and both ip ranges are seen as "connected" routes, so that would explain how they are able to communicate with each other.

 

It looks like 192.168.10.x range is utilised first and when the ips are exhausted the ips in the 192.169.12.x range, which is set as secondary then gets distributed.

 

It seems to work but because this is the first time I have tried this, I just wanted to know if anyone has tried this method and had any other issues with it?

 

 

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