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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>
Router>enable
Router#config termin
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#int Ser0/0/0
Router(config-if)#ip address 172.16.199.228 255.255.255.252
Bad mask /30 for address 172.16.199.228                 <--- HERE
Router(config-if)#

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

Thanks you! :)

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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
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1 Answer

up vote 6 down vote accepted

172.16.199.228 is the network address. You need to use 172.16.199.229 or .230

Output of ipcalc:

Address:   172.16.199.228       10101100.00010000.11000111.111001 00
Netmask:   255.255.255.252 = 30 11111111.11111111.11111111.111111 00
Wildcard:  0.0.0.3              00000000.00000000.00000000.000000 11
=>
Network:   172.16.199.228/30    10101100.00010000.11000111.111001 00
HostMin:   172.16.199.229       10101100.00010000.11000111.111001 01
HostMax:   172.16.199.230       10101100.00010000.11000111.111001 10
Broadcast: 172.16.199.231       10101100.00010000.11000111.111001 11
Hosts/Net: 2                     Class B, Private Internet
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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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