subnet expansion

[mialbert]

I have a subnet programmed in a c2951 as 192.168.70.0 255.255.254.0 which provides 512 addresses.  this needs to be expanded to accomodate 1000 addresses.  when i program 192.168.70.0 255.255.252.0(or 192.168.70.0 0.0.3.255)the router converts it to 192.168.68.0.  just verifying that those subnets are equivalent and that the ip work is ok. 

[cadet alain]

Hi,

with 255.255.252.0 or /22 the subnet increment is  256-252= 4 so the  subnet number whose  192.168.70.0 is a member IP address of is the 192.168.68.0 subnet with a range of valid host IPs of 192.168.68.1 - 192.168.71.254

so the IP you entered  for this mask is a valid host IP not a subnet IP.

Edited the host range 

Regards.

Alain

Ce message a été modifié par: cadet alain

[Jon Marshall]

It wiil convert it because that is how subnettting boundaries work ie. when you enter 192.168.70.0 255.255.252.0 the router calculates it like this -

252 is the important octet. 256 - 252 = 4 so the networks goes up in 4's ie.

192.168.0.0 255.255.252.0 (/22)

192.168.4.0 /22

192.168.8.0/22

etc.

192.168.60.0/22

192.168.64.0/22

192.168.68.0/22  <-- this covers 192.168.70.0 because the next network entry is -

192.168.72.0/22

so your available network is 192.168.68.0/22, host addresses are 192.168.68.1 -> 71.254 with 192.168.71.255 being the broadcast address.

Jon