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New Member

Interview Question

I was asked a question concerning an error that is very common when you configure a subnet on a frame-relay subinterface? The error was something about invalid/bad ip address, the interviewer wanted me to tell him how to prevent this. I believe he was looking for a specific command!

Just wondering!

  • Other Network Infrastructure Subjects
Cisco Employee

Re: Interview Question

Following web site has errors and their explanation relating to entering ip addresses on router interfaces. This might be of some help:


Re: Interview Question

There has to be more to the scenario for there to be a problem. In general a mask of means that you can have 2 host addresses off the network, which is fine. If the host or network addresses happen to overlap some other interface, then there would be a problem and an error would be generated. But otherwise, using this mask with no other information as to what may conflict should be fine.

Cisco Employee

Re: Interview Question

If you check on a router you will find that you are able to configure a /30 mask on a frame relay subinterface with out a problem.

Was the scenario given to you more specific in any way ?

New Member

Re: Interview Question

I have run into that error as well, and in my case it didnt have anything to do with the interface.

If you attempt to configure an ip on an interface, and you get the error "invalid/bad ip address", then it is one of 3 things.

1. you need to enter the command "ip classless"

2. you need to enter the command "ip subnet-zero"

3. you are trying to assign a network/broadcast ip to an interface (which is impossible)

Hope that helps

New Member

Re: Interview Question

Sounds like he was looking for "ip classless"