Subnet Mask setting on DHCP

[ccie2b2004]

I have a private set of IP giving to us by our internet provider. They told us to use Ips 10.1.142.128 with a subnet mask of 255.255.255.128. Now that i have some free time in my hands, I was checking some computers Ipconfig and noticed that some of them are getting their IP with a subnet mask of 255.0.0.0 All my servers have static IPs with the 255.255.255.128 subnet mask as indicated by our internet provider, so when I checked DHCP properties, it has the subnet mask as 255.0.0.0 but IT IS GRAYED OUT and I cannot changed it. I tried to create another scope with the 255.255.255.128 but it gave me an error telling me that either I have a similar scope, or the subnet mask in incorrect. My servers are Win2K and all my PC's are Win98SE

Any thoughts??? help?

Thanks

 

[yizhar]

HI.

To change the subnet mask on the DHCP server, you need to delete the existing scope and then create a new one.

Before doing so, check and write down the exclusions and reservations if any on the current scope, and also the scope options. Also write down the number of current active leases, so you can compare it with the new scope.

This will create a new database and might cause some problems, so when doing such a change it is a good idea to reboot all workstations afterwards.
The workstations will request the same ip address that they currently have, so the new scope will be updated afterwards and you will not have a big mess if any at all.

Bye
Yizhar Hurwitz

http://come.to/yizhar

http://teachers.sivan.co.il/yizhar

 

[doomhamur]

First: 255.255.255.128 is an invalid subnet mask. it means you have no space for a network number and no hosts. see

http://www.subnetonline.com.

whatever your isp is telling you to do, they are incorrect and i would be suprised if you actually could access the internet.

I would get a router (like a nextland 800) use it to get a dynamic ip from your isp and use it for your internet gateway. It can save you alot of problems with network security.

make your router 192.168.1.1 and your subnet 255.255.255.0
this gives you 254 ip addresses for your network. Doomhamur
Network Engineer
"Certifications? we dont need no stinking certifiaction."

 

[ccie2b2004]

Hello Doomhamur and thank you for your reply. I guess I have to be a bit more specific so you guys can understand my situation: I have about 6 public IP addresses provided by my internet provider. We have a T1 connection to my router. The router is doing the masking, and also points the private IP address of one of the routers cards with the public IP address of the other card (the router is a CISCO 1720). So all my PCs get's the gateway information (internal IP address from the router) with DHCP. Internet works fine, and I have not issues until I started to learn how to use the Fluke Network inspector 5. This software told me that the subnet mask is incorrect, and that is how I realized that my DHCP was configured incorrectly (please read my first post) One more thing I noticed a while back (which is why I started using the Fluke tool) in network neighborhood in my PCs and server only appear a hand full on PC names -netbios names-, not all of them (maybe about 15 instead of the 50 or so that it should show) So it lloks like my problems is growing by the minute froma simple DHCP error in configuration to ..... who knows what.

Any ideas?? Thanks luis

 

[doomhamur]

Hmmm....ok, it makes a little more sense.

1. do your pc's and servers use your public ip addresses? or are you using a private ip address.

2. if you are using a private ip, 255.255.255.128 is ilegal, use 255.255.255.0 instead.

3. if you are useing the public ip addresses, dont. use a private subnet.

Thanks Doomhamur
Network Engineer
"Certifications? we dont need no stinking certifiaction."