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I am using the GNS3 simulator, and I need to connect two Cisco C7200 routers.

When I enter the ip address 126.0.0.4 255.255.255.252 command, I get Bad mask /30 for address 126.0.0.4.

Ron Maupin
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sinzou
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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Dec 25 '18 at 08:59

2 Answers2

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That is because 126.0.0.4/30 is the network address, not a host address. See the answer to How do you calculate the prefix, network, subnet, and host numbers? for how to calculate that.

For a /30 network, there are two host addresses: subnet + 1 and subnet + 2. In your particular example, that would be 126.0.0.5 and 126.0.0.6.

Ron Maupin
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126.0.0.4/30 is the network address. To work, the IP of the first host should be 126.0.0.5/30(Gateway) and the second host 126.0.0.6/30

Pedro Ferreira
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