Bad Subnet Mask.

Nishesh.Prasad

Excuse me if the question sounds too obvious, but i cant figure out the logic behind the following :

Router(config)#interface e0/0
Router(config-if)#ip address 192.168.1.2 255.255.255.0
Router(config-if)#no shutdown
%LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up
Router(config-if)#interface e0/1
Router(config-if)#ip address 192.168.2.0 255.255.255.0
Bad mask /24 for address 192.168.2.0


i'll explain. I have got two routers connected to each other via e0/1 on Router_1 & e0/0 on Router_2. I have'nt configured the interfaces on Router_2 yet. On Router_1, i have configured e0/0 to have an IP of 192.168.1.0 /24. The interface is enabled. When i configure e0/1 on Router_1 to have an IP of 192.168.2.0 /24, i get the following msg : Bad mask /24 for address 192.168.2.0. Is'nt 192.168.1 & 192.168.2 two differrent network Ids under /24 ? Whats the reason behind this ?

fyi - m using a 4550 on both ends, but i suppose that shud'nt matter.

darkerosxx

Try 192.168.2.1. You can't use a .0 on a /24 subnet. I'm not sure why it didn't tell you that for the 1.0 assignment.

astorrs

Yeah, thats the network address.

suffah

Like the others have said, you're using the network address. You also can't assign the last address in a network (well it will let you but you'll have problems) since it's used as the broadcast address.

Nishesh.Prasad

Sorry guys that was a typo ... i mean i assigned 192.168.2.1 to the Interface e0/1 on Router_1 and then encountered the "Bad Subnet Mask" error. Any thoughts ? Just so that you know, this is under Netsim and not a Real Lab scenario.

astorrs

I would double-check the syntax and make sure you didn't make a typo in the config. The command:

ip address 192.168.2.1 255.255.255.0

should work fine.

Nishesh.Prasad

M pretty sure there were'nt any typos on the CLI.

astorrs

Can you repeat the lab just to make sure?

Paul Boz

Probably your sim. 192.168.2.1 / 24 is a good address and mask. Try to use a different IP address (192.168.1.1 255.255.255.0, 10.0.0.1 255.0.0.0 etc)

Nishesh.Prasad

Any other IP outside 192.168 works ok ... but as per /24 the Network ID should be 192.168.1 and not 192.168 ! ....oh man !

darkerosxx

Are you saying it won't allow you to assign anything from the 192.168 network? If that's true, it's just now allowing you to assign private addressing. Use something outside of it.

Nishesh.Prasad

Private IP ? .... they are ALL supposed to be Private IPs ... are'nt they ?

astorrs

Try 10.9.8.1 and 10.11.12.1 or something (both /24)

itstudent

This same issue confronted and confounded me for a bit. I have 4 older routers - 2 2501's and 2 4000's. It's a real pain when you are trying to do a lab and you get beat up from an old IOS. The resolution for the bad subnet mask for me was to use the ip subnet-zero command.

R1(config)#ip subnet-zero
R1(config)#int e0
R1(config-if)#ip add 192.168.2.3 255.255.255.224
R1(config-if)#no shut
R1(config-if)#exit