Changing subnet

[bodminman]

Hi there,

 

Over the half term I want to change the subnet for our IP range to give us some breathing space.

 

What order is it best to do this? Router then Static IP devices?

 

Thanks

[Michael]

There's no easy way around this without some downtime. The order is probably your server(s) first, including modifying your DHCP scope, your router and then your PCs with static configurations.

[Duke5A]

You could always spin up another VLAN and gradually migrate over to it if you can get to everything at once.

[bodminman]

You could always spin up another VLAN and gradually migrate over to it if you can get to everything at once.

 

Could do but we don't have the best switching infrastructure in place to sort this out. I'm currently awaiting approval of some funds to get the switches replaced.

[twin--turbo]

who looks after your ISP router, do you use an internal proxy and block all other outbound traffic.

 

 

What is your current network subnet? simply changing the mask on all devices or via DHCP will give you more headroom. it can be done without downtime.

 

Rob

[bodminman]

who looks after your ISP router, do you use an internal proxy and block all other outbound traffic.

 

 

What is your current network subnet? simply changing the mask on all devices or via DHCP will give you more headroom. it can be done without downtime.

 

Rob

 

Hi Rob,

 

We have a Lightspeed box doing inline filtering and our Sonicwall (NSA240) is setup to just allow traffic out from that and a few other devices.

 

Our current setup is 192.168.0.0/255.255.254.0 and I just want to change the mask to 255.255.252.0 to double our IP range so that I can expand the DHCP scope as we're regularly now getting to the point where we have only 20 - 30 IPs left.

 

Thanks

[twin--turbo]

The recomended no of hosts per broadcast domain is 510 as in a /23 subnet. Which is where your at.

 

Depending on your traffic and how many extra hosts there are doublign to a /22 may be a bad idea.

 

Rob

[bodminman]

The recomended no of hosts per broadcast domain is 510 as in a /23 subnet. Which is where your at.

 

Depending on your traffic and how many extra hosts there are doublign to a /22 may be a bad idea.

 

Rob

 

We need to cater for only an approx 150 extra IPs.

[bodminman]

What is your current network subnet? simply changing the mask on all devices or via DHCP will give you more headroom. it can be done without downtime.

 

Rob

 

@twin-turbo. - can you please describe an example of how this could be done without downtime?

 

Thanks

[twin--turbo]

@twin-turbo. - can you please describe an example of how this could be done without downtime?

 

Thanks

 

In Theory ( last time I did this was ~8 years ago )

 

Your original subnet is 192.168.0.1 - 192.168.1.254 ( bcast 192.168.1.255 )

Your new subnet will be 192.168.0.1 -192.168.3.254 ( bcast 192.168.3.255 )

 

If you change you change a server mask to /22 it can still arp broadcast to all hosts in the new subnet (bcast on 192.168.3.255). and so long as you keep it's IP in the original portion of the subnet, other hosts should be able to arp broadcast to it on 192.168.1.255.

 

the key is to keep all hosts in the original subnet range until all the work is done. and to make 150% sure that 192.168.1.255 is not put into a DHCP scope.

 

 

It's easy enough to test. Just get a server or client your not worried about. Change the mask and check it can ping.

 

 

 

However, I would seriously look at splitting up the network into smaller broadcast domains by sticking a L3 switch between the network and the Lightspeed (I guess this is transparent?) and gettign some vlan routing going on.

 

 

Rob

[bodminman]

In Theory ( last time I did this was ~8 years ago )

 

Your original subnet is 192.168.0.1 - 192.168.1.254 ( bcast 192.168.1.255 )

Your new subnet will be 192.168.0.1 -192.168.3.254 ( bcast 192.168.3.255 )

 

If you change you change a server mask to /22 it can still arp broadcast to all hosts in the new subnet (bcast on 192.168.3.255). and so long as you keep it's IP in the original portion of the subnet, other hosts should be able to arp broadcast to it on 192.168.1.255.

 

the key is to keep all hosts in the original subnet range until all the work is done. and to make 150% sure that 192.168.1.255 is not put into a DHCP scope.

 

 

It's easy enough to test. Just get a server or client your not worried about. Change the mask and check it can ping.

 

 

 

However, I would seriously look at splitting up the network into smaller broadcast domains by sticking a L3 switch between the network and the Lightspeed (I guess this is transparent?) and gettign some vlan routing going on.

 

 

Rob

 

Thanks for taking the time to type/explain that Rob.

 

I will look at getting the network serparated in the summer of 2014. However, we need to make this change rather urgently so just need a quick fix for now.

[dave.81]

We had to do the same recently. Did during a bank holiday, swapped the DHCP range over, swapped static IP's on servers, then switches, printers, wireless etc etc and reboot clients. All working find with the extra although i agree it's not ideal having a range this size and need to split off into VLANS but that can be another day(year!).