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Im trying to do a practice in packet tracer. Im configuring a 1841 Router (but the problem happens in all routers).

When I try to set an IP address with a mask different of the by defect mask for this Class of address (using VLSM), the router said me that the mask is incorrect (Bad mask) and don't change anything.

I will implement a classless routing protocol (RIPv2).

Here the line of commands:

Router#config termin
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#int Ser0/0/0
Router(config-if)#ip address
Bad mask /30 for address                 <--- HERE

How can I set an IP address with a no by defect mask?

Thanks you! :)

share|improve this question
If you don't know it already, go look up wildcard mask vs subnet mask or that will be your next question when you do rip :-) – Kyle Brandt Feb 10 '10 at 19:02
up vote 7 down vote accepted is the network address. You need to use or .230

Output of ipcalc:

Address:       10101100.00010000.11000111.111001 00
Netmask: = 30 11111111.11111111.11111111.111111 00
Wildcard:              00000000.00000000.00000000.000000 11
Network:    10101100.00010000.11000111.111001 00
HostMin:       10101100.00010000.11000111.111001 01
HostMax:       10101100.00010000.11000111.111001 10
Broadcast:       10101100.00010000.11000111.111001 11
Hosts/Net: 2                     Class B, Private Internet
share|improve this answer
Ok, I should take a very cold shower. Well, at least this question could be useful for more people with the same problem. Thanks you very much, good answer ;) – a0rtega Feb 10 '10 at 19:05
Heh, happens to everybody. Get ipcalc and use it all the time ;) – MikeyB Feb 11 '10 at 2:12

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